Paul v Cooke

Background 4On 15 July 2003, Mrs Paul consulted her general practitioner, Dr Dostal, complaining of headaches, seeing flashing lights, nausea and feeling faint. She told Dr Dostal that her twin sister had died in 1989, at the age of 37, as the result of a ruptured berry aneurysm. He referred her for an angiogram, which was performed on 21 July 2003, and reviewed and reported on by Dr Cooke on the same day. Dr Cooke reported that it was normal. It is not disputed that he thereby breached a duty of care, in that a prudent practitioner in his position exercising reasonable care would have identified and reported the aneurysm.

Berry aneurysms and their treatment 5In 2003 - as in 2006 - there were three potential courses for treatment of such an aneurysm. The first was conservative management - that is, keeping the aneurysm under observation with a view to intervening if some relevant change were detected or some symptoms - such as a "warning headache", referred to below - appeared. The second was "clipping", an open neurosurgical procedure to remove the aneurysm. The third was "coiling", a closed endovascular procedure to obliterate the aneurysm. 6The major reason for treating a berry aneurysm is that, untreated, there is a risk that the aneurysm will rupture spontaneously. In a joint report, three expert neurosurgeons - Professor Stoodley, Professor Morgan and Professor Allan - quoted the risk of spontaneous rupture as 1-2%; this was not further explored, but it apparently refers to risk over the patient's lifetime, rather than per annum. However, spontaneous ruptures have a 60% mortality rate, and the survivors have a significant incidence of permanent neurological deficits, which are not avoidable by treatment after the initial spontaneous rupture. It was such a spontaneous rupture that killed Mrs Paul's twin sister. 7Each of the procedures also has its own risks, including a risk of intra-procedural rupture. In coiling, this risk arises in various ways, the most likely being though penetration by the microcatheter or a coil into the wall of the aneurysm. In clipping, the risk of rupture arises from manipulation of the aneurysm. Based on the joint report of the experts:

• the percentage risk that the aneurysm would rupture during a hypothetical clipping procedure in 2003 was greater (5-10%) than the risk that the aneurysm would rupture during the coiling procedure that took place on 8 March 2006 (1-2%);
• the risk that the aneurysm would rupture during a hypothetical coiling procedure in 2003 was the same (1-2%) as the risk that the aneurysm would rupture during the coiling procedure that took place on 8 March 2006 (1-2%);
• the risk that the plaintiff would suffer stroke and her consequential injuries as a result of a rupture of the aneurysm during a clipping procedure, whether in 2003 or 2006, was 5%; and,
• this was less than the risk that stroke and injuries would result from a rupture of the aneurysm during a coiling procedure, whether in 2003 or 2006, which was 50%. (This difference is attributable to the relative ease with which a rupture can be treated, and the situation retrieved, in the course of an open "clipping" procedure as opposed to in a closed "coiling" procedure.) 8In addition to the risk of intra-procedural rupture, there are other risks associated with each procedure. For clipping, these include that the procedure is more invasive than coiling, headaches, scarring, slower post-operative recovery, bone flap infection, epilepsy, leaking of cerebrospinal fluid, haematoma and subtle neurological changes. According to an article published in The Lancet on 12 July 2003, which the experts adopted, the general morbidity and mortality rates associated with clipping in patients with no history of subarachnoid haemorrhage were 12.6%. Coiling is a less durable treatment than clipping (which is definitive), in that coiling does not always permanently obliterate the aneurysm. According to The Lancet article, the overall morbidity rate for coiling in the same group of patients was 9.8%.

Between 2003 and 2006 9Mrs Paul's aneurysm did not rupture between 2003 and 2006. Its shape and size, and the thickness and strength of its walls, did not change during that period. (The Plaintiff abandoned an allegation, once pleaded, that between 2003 and 2006 there was a thinning or weakening of the wall of the aneurysm, the experts having agreed that it could not be said that it was more likely than not that that had occurred.) 10In January 2006, Mrs Paul consulted a general surgeon, Dr Coleman, as she was concerned about some possible breast abnormalities. Dr Coleman, having taken Mrs Paul's history - including the death of her sister in 1989 - ordered a cerebral CT angiogram. This second angiogram was performed on 23 January 2006, and was reported on by Dr Lau, radiologist, as demonstrating a 7-8mm aneurysm arising from the right anterior cerebral artery near the anterior communicating branch. 11On 1 February 2006, upon referral from her general practitioner, Dr Goor, Mrs Paul, accompanied by her husband, was seen by Dr Jerry Day, a neurosurgeon practicing in Wollongong. Dr Day reviewed the 2003 CT angiogram on which Dr Cooke had reported, and concluded that it had been wrongly interpreted as normal, as it demonstrated an aneurysm arising from the anterior cerebral artery near the anterior communicating branch identical in anatomy to that seen on the cerebral CT angiogram of 23 January 2006. 12Dr Day had a lengthy discussion with Mrs Paul about the options for treatment, and the potential risks of each of them - including death, rupture of the aneurysm, haemorrhage and stroke, with resulting physical and mental disabilities. Mrs Paul - whose evidence was that she was "blown away" to find out that she had an aneurysm, was scared that she was going to die, and was "extremely, extremely concerned" and "sick to the stomach" that she had something like a "time bomb" in her head - does not actually recall discussing treatment options on this occasion, but accepts that they did. She accepts that there was discussion of the three options of clipping, coiling, and having no treatment. Unsurprisingly, in the light of what had happened to her sister, she was most concerned about the risk of the aneurysm rupturing, and (based on the documentary record) accepts that Dr Day explained that risk. She does not recall whether they discussed the risks of having no treatment, as she had already eliminated that option: "My identical twin was dead, I had to have something done. I don't recall if we discussed it but I ruled it out anyway". Dr Day recommended coiling, but said that he was going to discuss with colleagues which was the better approach. 13When asked whether, in the light of Dr Day's explanation of the pros and cons of the various approaches, she understood that there was a choice to be made, she answered that she was seeing a neurologist for advice, and went along with whatever method he suggested. She accepted that Dr Day probably identified death and haemorrhage among the risks of coiling and clipping, though she did not recall it: "Probably; he probably discussed all these things, but I don't recall, it all goes over your head. I took the advice of the neurologist. It was not really my choice". When it was suggested to her that Dr Day told her that she needed to think about it, so that she could choose between them, she answered: "I didn't understand it that way". She did not recall discussing the options with her family, but accepted that they obviously would have done so. 14After the consultation, Dr Day presented the case to the weekly cerebrovascular conference between specialists from Wollongong, St George, Prince of Wales and St Vincent's hospitals, following which he made a firmer recommendation for coiling, and said that he had spoken to other neurologists who agreed that coiling was the best approach. On 2 February 2006, he referred Mrs Paul to Dr Parkinson, for "evaluation and probable endovascular treatment". 15On 9 February 2006, Mrs Paul, accompanied by her husband, had her first consultation with Dr Parkinson, who did not give evidence at the hearing, but whose letters to Dr Day, reporting on his consultations with the plaintiff on 9 and 23 February 2006, were in evidence. Dr Parkinson gave her a detailed explanation of the risks of both endovascular coiling and surgery, including overall morbidity rates. Mrs Paul said that she had little memory of those days, but accepted, based on the documentary record, that they discussed that there were three treatment options, and that Dr Parkinson took her through what was involved in coiling, and in clipping. She clearly understood that clipping involved open surgery on the brain, through cutting open the skull, and that there were obvious risks associated with cutting open the skull and brain. She also understood that the coiling procedure involved passing a catheter through the arteries to reach the aneurysm. Dr Parkinson told her that coiling was a 24-hour procedure, so that she would be out the next day, whereas open surgery was more invasive and more dangerous, and had a longer recovery time. Mrs Paul accepted, based on the contemporaneous correspondence, that he said that there was a risk of rupture associated with coiling. On this occasion, Dr Parkinson recommended coiling, at least provisionally, subject to discussion with his colleagues Professor Stoodley and Dr Wenderoth, and referred Mrs Paul for another CT scan. She said that as he advised coiling, she did not really concentrate when he was talking about clipping. Mrs Paul says that she did not thereafter discuss the options with her husband; I infer that this was because she intended to follow the doctor's recommendation. 16Mrs Paul had the further CT scan on 20 February 2006, which did not reveal any sign that the aneurysm had ruptured, or had changed in size or shape or in any other way. On 23 February 2006, Mrs Paul was seen by Dr Parkinson a second time. He discussed with her the recent CT scan, and indicated that he was confirmed in his recommendation that coiling was the best way to proceed. When it was put to her that he again discussed that there was the option of clipping, she answered, "my main memory of that is that coiling was the best way". She was then booked in for a coiling procedure at Prince of Wales Hospital on 8 March 2008.

A warning headache? 17Prior to a spontaneous rupture of an aneurysm, there is sometimes experienced - though by no means invariably - a headache, called a "warning headache". Such headaches are not well understood: Professor Stoodley explained that it used to be thought that it was a warning bleed, but thought it pretty clear now that that was not so; he said that it may be that it was a sudden enlargement of the aneurysm or some change in its structure that we do not understand, "so there is something that happens that causes a headache". 18Mrs Paul, who had a life-long history of headaches, and a family history of migraines, had been suffering bad headaches in the week preceding her consultation with Dr Day, which Dr Day suspected were stress related. At her first consultation with Dr Parkinson, Mrs Paul had been told that if she had any symptoms of violent headaches, vision problems or tremors, then she should get to a hospital as soon as possible. On 3 March 2006, she presented at Shellharbour Hospital with a headache, photophobia and nausea. She described this as the worst headache she had ever experienced; however, it resolved after treatment with analgesia. She underwent a further CT scan that day, which revealed no sign of any rupture of or other change in the aneurysm. Nor did a lumbar puncture and subsequent blood tests suggest any rupture. 19In the course of the concurrent evidence of the experts, it emerged that the Plaintiff wished to contend that this was a "warning headache", in the light of which "Mrs Paul was unlikely to be at the same level of risk of rupture in March 2006 as she was in 2003"; in other words, the Plaintiff sought to contend that this illustrated an increase in the susceptibility of the aneurysm to rupture prior to the 8 March 2006 procedure - a finding that would support the Plaintiff's case on causation, because it would show that during the period while the aneurysm remained untreated following Dr Cooke's failure to diagnose it, its propensity to rupture had increased. 20However, this case had not been pleaded. The matters relied upon to establish causation, as pleaded in the Third Amended Statement of Claim, included that the magnitude of the general risk of rupture of the aneurysm during clipping in July 2003 would have been the same as the risk of rupture during coiling on 8 March 2006 (par 21(a)); that the magnitude of the risk of rupture and stroke during clipping in July 2003 would have been less than that of rupture and stroke during coiling on 8 March 2006 (par 21(b)); and that the magnitude of the general risk of rupture during coiling in July 2003 would have been the same as the risk of rupture during coiling on 8 March 2006 (par 24(a)). In other words, the Plaintiff's pleaded case was that there was no increase in the risk of rupture between 2003 and 2006 (though it was alleged that there was an increase in the risk of stroke and injuries following rupture, by reason that she underwent coiling rather than clipping). 21Paragraphs 21 and 24 were added by the Further Amended Statement of Claim, with the Defendant's consent, prior to giving which the Defendant had sought, and the Plaintiff had provided, particulars of the facts and matters relied upon in support of the contention that there was any difference in the magnitude of risk as between 2003 and 2006. The Plaintiff's response was that, in her specific case, there was an increase in risk, and the facts and matters relied upon were set out in the "numerous expert evidence, served by all parties and the clinical records for the coiling procedure". An increase in risk related to a "warning headache" was not referred to in any of the expert evidence served by either party. 22Moreover, an allegation, formerly pleaded, that the wall of the aneurysm would have been weaker and thinner on 8 March 2006 than in July 2003 (formerly, pars 21(c) and 24(b)) was deleted by amendment made at the outset of the trial, when leave to substitute for it an allegation that it may have been thinner and weaker at the later date was refused, essentially on the basis that, given the agreed and undisputed position of the experts that it was not more likely than not that the wall was thinner, a mere possibility that it was would be irrelevant [Paul v Cooke [2011] NSWSC 959]. 23Such a possibility, associated with the "warning headache", was not the subject of any questions put to the experts when they conferred prior to the hearing, nor was it adverted to in the plaintiff's opening submissions. 24Dr Day, whose letter of 1 February 2006 had referred to Mrs Paul as having "a life long history of headaches" which had been worse in the last week - he suspected due to stress - and noted that she had "never had an explosive headache suggestive of any degree of subarachnoid haemorrhage", was the Plaintiff's witness, and could have given relevant evidence on this issue; but the Plaintiff led no evidence from him on the topic, in particular to qualify or contradict the view expressed in his letter that the headaches the plaintiff was experiencing were stress-related. Had such evidence been led and its asserted relevance known, his 1 February letter would have provided a firm foundation for effective cross-examination - an opportunity of which the Defendant was deprived, as he was also of the opportunity to obtain and adduce evidence and/or advice from appropriately qualified experts. 25As pleaded, and until this issue emerged on the third day of the trial, the Plaintiff's case was that the risk of rupture did not increase between 2003 and 2006. It was on that basis that the case proceeded. Having regard also to the disadvantages that the Defendant has suffered in meeting an allegation that there was an increased risk of rupture associated with a warning headache, as a result of the manner in which the issue belatedly emerged, I would not permit that allegation now to be agitated. 26But lest I be wrong in that respect, I would in any event not be persuaded on balance that this was a "warning headache". The plaintiff had a history of headaches, and had been suffering headaches in the week prior to her visit to Dr Day, which he suspected were stress related. She was very upset, and extremely anxious. There was no evidence of any haemorrhage of, or any other physical change in, the aneurysm prior to the procedure: including in the CT scan taken at the time of the headache on 3 March 2006. Professor Stoodley said that he could not say - even on the balance of probabilities - whether or not it was a warning headache, there were factors for and factors against; had she gone on to have a spontaneous haemorrhage, it would retrospectively be seen as a warning headache - but there was not a spontaneous rupture, rather there was an inter-operative rupture. Dr Allan likewise could not give an answer either way on the probabilities. The Plaintiff has not proved that, more probably than not, this was a "warning headache". 27And even if it was a "warning headache", I would be unpersuaded that it involved or was associated with any increase in the risk of rupture during the coiling procedure. Professor Stoodley said that there was an increased risk of spontaneous rupture associated with warning headaches; but while in respect of intra-procedural ruptures there was a "theoretical" association, such association was not proven. He agreed that if there was no change in the size or shape or physical characteristics of the aneurysm or the strength or thickness of its wall (which was not in issue, and the 3 March CT scan confirmed), then the warning headache would not probably be linked to any increase in risk of rupture during the procedure. Dr Allan agreed. 28Accordingly, I would not permit the Plaintiff to maintain a case based on the "warning headache", but if such a case were advanced, on the available evidence I would not be satisfied that the plaintiff had a warning headache, nor (if she did) that it was associated with any increased risk of intra-procedural rupture.

The 8 March 2006 procedure 29Mrs Paul signed a consent form for the procedure on 6 March 2006, recording that one of the risks brought to her attention, yet again, was that of stroke. 30On 8 March 2006, Mrs Paul underwent the coiling procedure, at the Prince of Wales Hospital in Sydney. During the procedure, the aneurysm ruptured, causing a subarachnoid haemorrhage, as a result of which Mrs Paul suffered a left front lobe infarction (a stroke) causing a right hemiparesis, expressive aphasia and cognitive impairment.

The mechanism of the rupture 31The rupture occurred during the coiling procedure, after deployment of the first coil. The radiologist (Dr Wenderoth) made handwritten notes of the procedure, recording that the aneurysm ruptured "at the neck during balloon inflation/positioning of the first coil". The typewritten notes of the procedure, prepared on 5 April 2006, state "the aneurysm ruptured after following [sic] inflation of the balloon when the aneurysm was catheterized". 32The experts agreed that it was likely that the aneurysm ruptured at the time of the balloon inflation and insertion of the first coil, and that the most likely mechanism was penetration by the microcatheter or a coil into the wall of the aneurysm. 33The plaintiff submitted that, based on the contemporaneous handwritten operation note, it was more likely that inflation of the balloon was responsible for the rupture, and that if coiling had been performed in 2003, a balloon would not have been employed and there would have been no risk of the actual mechanism of rupture that eventuated. Use of a balloon in a coiling procedure was a technique that had been available from the outset of coiling, although it does not appear to have been widely used in Australia in 2003. The balloon is inserted into the artery for the purpose of preventing escape of the coils from the aneurysm into the circulation. The risks associated with the inflation of the balloon are more to do with rupture of the artery than of the aneurysm itself. Dr Allan adhered to the view that penetration by the microcatheter or a coil was the more likely explanation during the concurrent evidence of the experts, and although he accepted that the inflation of a balloon could tear the neck of the aneurysm, he said that this would be a rare occurrence, and had it happened he would have expected there to be a more catastrophic haemorrhage than was reported here. 34On the probabilities, the rupture was caused by penetration by the microcatheter or a coil into the wall of the aneurysm during the coiling procedure. Even if it were accepted that inflation of the balloon was the immediate cause, that was still inherent in the coiling procedure. As Dr Allan maintained, intra-operative rupture could occur during a coiling procedure, through either of the mechanisms of microcatheter penetration or balloon inflation, and even with the exercise of all due care and skill. Whatever the precise mechanism, there was no evidence that in this case it was attributable to operator negligence, and the experts agreed that such mishaps could not be totally avoided even by skilled, careful and prudent operators.

Scope of duty 35The first basis on which the defendant submitted that Dr Cooke should not be held liable in damages to Mrs Paul was that the duty of care of a diagnostic radiologist did not extend to taking reasonable care to avoid harm occasioned by treatment of the diagnosed condition, namely the aneurysm. It was submitted that his duty owed to the plaintiff did not include taking reasonable care to avoid a stroke occurring in the course of treatment of the aneurysm, which was an inevitable aspect of having the aneurysm and receiving treatment for it - a risk that may have occurred, with the same degree of probability, had he not breached his duty of care in reporting on the results of the angiogram; one which he could have done nothing to avoid; and one in respect of which he had done nothing to assume responsibility. 36However, "scope of duty" considerations are relevant primarily to whether or not there has been a breach of duty (which is admitted here), rather than to whether liability should be denied in respect of a proven or admitted breach. A negligent driver who injures a pedestrian may be liable for the complications occasioned by subsequent medical treatment, even though the driver has no duty of care in respect of that subsequent medical treatment. Once breach of duty is established, the question becomes one of causation. This is illustrated by the observations of the High Court in Mahony v J Kruschich (Demolitions) Pty Ltd [1985] HCA 37; (1985) 522 CLR 523 (at 528, 529) (citations omitted): A negligent tortfeasor does not always avoid liability for the consequences of a plaintiff's subsequent injury, even if the subsequent injury is tortiously inflicted. It depends on whether or not the subsequent tort and its consequences are themselves properly to be regarded as foreseeable consequences of the first tortfeasor's negligence. A line marking the boundary of the damage for which a tortfeasor is liable in negligence may be drawn either because the relevant injury is not reasonably foreseeable or because the chain of causation is broken by a novus actus interveniens. But it must be possible to draw such a line clearly before a liability for damage that would not have occurred but for the wrongful act or omission of a tortfeasor and that is reasonably foreseeable by him is treated as the result of a second tortfeasor's negligence alone. Whether such a line can and should be drawn is very much a matter of fact and degree... Where it is not possible to draw a clear line, the first tortfeasor may be liable in negligence for a subsequent injury and its consequences although the act or omission of another tortfeasor is the more immediate cause of that injury... When an injury is exacerbated by medical treatment, however, the exacerbation may easily be regarded as a foreseeable consequence for which the first tortfeasor is liable. Provided the plaintiff acts reasonably in seeking or accepting the treatment, negligence in the administration of the treatment need not be regarded as a novus actus interveniens which relieves the first tortfeasor of liability for the plaintiff's subsequent condition. The original injury can be regarded as carrying some risk that medical treatment might be negligently given. It may be the very kind of thing which is likely to happen as a result of the first tortfeasor's negligence. 37Nonetheless, the scope of the duty influences - though it does not control - the inquiry as to causation. Questions of causation must be determined within the legal framework of the relevant duty to take reasonable care to prevent a foreseeable risk of harm of the kind in issue [Chappel v Hart [1998] HCA 55, [7]; (1998) 195 CLR 232, 238 (Gaudron J)]. In this respect, there is an "interrelationship that exists between questions of legal responsibility and causation" [Modbury Triangle Shopping Centre v Anzil [2000] HCA 61, [37]; (2000) 205 CLR 269], and an incorrect delineation of the duty of care can lead to error in determining causation [cf Modbury, [40]]. As Basten JA has recently said, in Wallace v Kam [2012] NSWCA 82 (at [164]), "any attempt to treat elements of causation as entirely separate and distinct is doomed to fail in contestable cases, as is a rigid compartmentalisation of duty, breach and causation ...". 38Thus, the circumstance that Dr Cooke's duty of care did not extend to responsibility for a procedure that may have been occasioned by his diagnosis (or lack thereof) is not of itself reason to deny that he is liable for damage done in the course of such a procedure; once breach of duty is established, the question is one of causation. Although the inquiry as to causation is influenced by the scope of the relevant duty, this is more appropriately considered under the "scope of liability" element of causation, which is a different notion from "scope of duty".

39At common law, the test for causation was the "common sense" test enunciated in March v E and MH Stramare Pty Ltd [1991] HCA 12; (1991) 171 CLR 506, 515 (Mason CJ), 523 (Deane J), 531 (McHugh J). According to this test, it was necessary but not sufficient that the harm would not have occurred "but for" the negligent act or omission of the defendant: while the "but for" test had an important role in the resolution of the issue of causation as a negative criterion, it was not comprehensive [Tabet v Gett [2010] HCA 12, [112]; (2010) 240 CLR 537 (Kiefel J)]. 40In the present case, however, the question of causation falls to be resolved under (NSW) Civil Liability Act 2002, s 5D, which provides as follows: 5D General principles (1) A determination that negligence caused particular harm comprises the following elements: (a) that the negligence was a necessary condition of the occurrence of the harm (factual causation), and (b) that it is appropriate for the scope of the negligent person's liability to extend to the harm so caused (scope of liability). (2) In determining in an exceptional case, in accordance with established principles, whether negligence that cannot be established as a necessary condition of the occurrence of harm should be accepted as establishing factual causation, the court is to consider (amongst other relevant things) whether or not and why responsibility for the harm should be imposed on the negligent party. (3) If it is relevant to the determination of factual causation to determine what the person who suffered harm would have done if the negligent person had not been negligent: (a) the matter is to be determined subjectively in the light of all relevant circumstances, subject to paragraph (b), and (b) any statement made by the person after suffering the harm about what he or she would have done is inadmissible except to the extent (if any) that the statement is against his or her interest. (4) For the purpose of determining the scope of liability, the court is to consider (amongst other relevant things) whether or not and why responsibility for the harm should be imposed on the negligent party. 41Under Civil Liability Act, s 5E, a plaintiff bears the onus of proving, on the balance of probabilities, any fact relevant to the issue of causation. Section 5D(1) has the effect that to establish causation requires a positive answer to two inquiries - factual causation, and scope of liability [Adeels Palace Pty Ltd v Moubarak [2009] HCA 48, [42]; (2009) 239 CLR 420, 443]. The position has recently been restated by the High Court, in Strong v Woolworths Ltd [2012] HCA 5 (7 March 2012), in the following terms (footnotes omitted): 18. The determination of factual causation under s 5D(1)(a) is a statutory statement of the "but for" test of causation: the plaintiff would not have suffered the particular harm but for the defendant's negligence. While the value of that test as a negative criterion of causation has long been recognised, two kinds of limitations have been identified. First, it produces anomalous results in particular cases, exemplified by those in which there is more than one sufficient condition of the plaintiff's harm. Secondly, it does not address the policy considerations that are bound up in the attribution of legal responsibility for harm. 19. The division of the causal determination under the statute into the distinct elements of factual causation and scope of liability is in line with the recommendations in the Final Report of the Committee convened to review the law of negligence ("the Ipp Report"). The authors of the Ipp Report acknowledged their debt to Professor Stapleton's analysis in this respect. The policy considerations that inform the judgment of whether legal responsibility should attach to the defendant's conduct are the subject of the discrete "scope of liability" inquiry. In a case such as the present, the scope of liability determination presents little difficulty. ... In particular cases, the requirement to address scope of liability as a separate element may be thought to promote clearer articulation of the policy considerations that bear on the determination. Whether the statutory determination may produce a different conclusion to the conclusion yielded by the common law is not a question which is raised by the facts of this appeal. 20. Under the statute, factual causation requires proof that the defendant's negligence was a necessary condition of the occurrence of the particular harm. A necessary condition is a condition that must be present for the occurrence of the harm. However, there may be more than one set of conditions necessary for the occurrence of particular harm and it follows that a defendant's negligent act or omission which is necessary to complete a set of conditions that are jointly sufficient to account for the occurrence of the harm will meet the test of factual causation within s 5D(1)(a). In such a case, the defendant's conduct may be described as contributing to the occurrence of the harm. 42In this case, four related features dominate the inquiry into causation. First, on the probabilities, the rupture was caused by mechanical means during the operative procedure. Secondly, it was not spontaneous; this is significant because, whereas a causative connection can be seen if, through failure to diagnose it, an aneurysm that had the potential to rupture spontaneously at any time was not treated and obliterated but remained in situ and then ruptured spontaneously, the same apparent connection does not exist where the rupture is not spontaneous but provoked by an intervention which involved broadly the same risks that would have been associated with a timely intervention. Thirdly, the risk of an intra-procedural rupture occurring on any one occasion was very slight - less than 1%; accordingly there was a high degree of probability that on any particular occasion there would not be such a rupture. Fourthly, this is not a case in which delay in diagnosis is associated with ongoing suffering or a deterioration in the patient's condition or increased difficulty in treating it - in contrast, for example, to the delayed diagnosis of a cancer.

Factual causation 43The ascertainment of factual causation under s 5D(1)(a) involves inquiring into whether the negligent conduct in question played a part in bringing about the relevant harm, and determining whether there was, on the part of the defendant, "historical involvement in the plaintiff suffering actionable damage" [Ruddock v Taylor, [2003] NSWCA 262, [86]; (2003) 58 NSWLR 269, 286 (Ipp JA)]. It requires proof that the defendant's negligence was a necessary condition of the occurrence of the particular harm [Strong v Woolworths Ltd, [20]]. This is the "but for" test and, because of the concurrent requirements of s 5D(1)(b), it is - as at common law - a necessary but not sufficient condition for establishing causation [Adeels Palace v Moubarak, 443 [45], [55]]. The answer is at least usually dependent upon a comparison of what would have occurred had the defendant not breached the duty of care, with what in fact occurred [Tabet v Gett, [140]].

What would have happened in 2003? 44In essence, the Plaintiff says that, if her aneurysm had been diagnosed in 2003, she would have undergone clipping then (rather than coiling), and that (on the probabilities) the aneurysm would have been permanently obliterated, without adverse consequence. More elaborately, the Plaintiff submits that had the diagnosis been made in 2003, (1) she would have been referred by Dr Day to Dr Morgan, (2) Dr Morgan would have recommended clipping, and (3) Mrs Paul would have acted on that recommendation. 45It is not in issue that, had the diagnosis been made in 2003, Mrs Paul's general practitioner would have referred her to Dr Day. Dr Day's evidence is that in 2003 he would have recommended clipping, and that he would have referred Mrs Paul to Professor Morgan, at Royal North Shore Hospital ("RNSH"). Although in cross-examination he said that he would not have indicated his recommended treatment until the plaintiff had seen Professor Morgan, to whose recommendation he would have deferred, I find that he would have indicated at least an inclination in favour of clipping at the initial consultation - just as he indicated an inclination in favour of coiling at the first consultation in 2006. 46Professor Morgan reported that it was more likely than not that, if Mrs Paul had been referred to him in 2003, he would have recommended clipping. The Defendant submits that it is by no means certain that the ultimate collective recommendation of all of the relevant medical practitioners consulted as a result of the referral to Professor Morgan would have been clipping, and points to the following matters. First, Dr Day's evidence was that, in 2003, the most experienced endovascular coiling unit, to his knowledge, was at RNSH, and that in referring the plaintiff to Professor Morgan, he would have understood that he was attaining not only the opinion of Professor Morgan himself, but also those of his team at RNSH who were experts in the field of endovascular coiling; indeed, one of the purposes of the referral was to gain a second opinion, and to open up the option of coiling. Secondly, it may be inferred - from what happened in 2006, when the plaintiff was diagnosed with the aneurysm, and Dr Day consulted with his colleagues at the weekly cerebrovascular conference, and Dr Parkinson consulted (or at least indicated his intention to consult) Dr Wenderoth and Professor Stoodley - that in 2003 Professor Morgan would have consulted with the other members of the endovascular coiling team at RNSH. Thirdly, the experts agreed that the nature and size of the plaintiff's aneurysm made it equally amenable to treatment by clipping or coiling, and in the light of the absence of any alteration in the physical characteristics of the aneurysm between 2003 and 2006, this would equally have been so in 2003. The Defendant's submissions then hypothesise that the endovascular group at RNSH, whose collective opinion would thus have been elicited by such a referral, may by then have been more inclined to favour the less invasive coiling procedure, including by reason of the recent (July 2003) report in The Lancet of the relative rates of morbidity of the two procedures. 47However, objectively, clipping was the predominantly favoured procedure in 2003. Dr Day says that he would then have recommended it. Professor Morgan says that he would then have recommended it (although illness precluded his opinion from being tested). The prospect that Mrs Paul would have been given different advice because of evolving views of the RNSH endovascular group is speculative. The conclusion that in 2003, more probably than not, Mrs Paul would have been referred to Dr Morgan, and that he would have recommended clipping, is inescapable - although he might well have mentioned the option of coiling, and referred to its less invasive nature. 48So advised, what would Mrs Paul have done? The answer to this is illuminated by her conduct in 2006. 49In my view, there is no doubt that she would have had treatment in 2003 had the diagnosis been made then, for exactly the same reasons that she had treatment in 2006. In the light of what had happened to her sister, she would have been most concerned about the risk of rupture and death, and would have excluded the option of conservative management. What she said of 2006 would have applied equally in 2003: "My identical twin was dead, I had to have something done. I don't recall if we discussed it but I ruled it [doing nothing] out anyway". 50As to what procedure she would have undergone, more probably than not she would have acted on the advice of her doctors. The Defendant submitted that Mrs Paul understood that the point of their recommendations was that she could make a choice, and that she understood (in 2006) that Dr Parkinson's recommendation for coiling had been made because it was a 24-hour procedure, in and out the next day, as against "open surgery which is more invasive and more dangerous". I accept, as the Defendant submits, that this was a material consideration for her, and would probably have been so if faced by the requirement to make the same choice in 2003. However, I also find that by far the weightier consideration in her mind was the recommendation of her treating medical practitioners. Her evidence that she acted on her doctors' recommendations was not only plausible but convincing. Although she accepted that she was angry with Dr Cooke, whom she no doubt blames for her condition, I do not find that this has influenced her evidence, which is consistent with her conduct in 2006: she accepted the advice she was given, without seriously questioning it. Significantly, Dr Day said that he would make clear which course was in his opinion the preferable option, and try to guide the patient to that option based on his professional opinion, rather than leaving the choice entirely open to patient. 51In 2003, as in 2006, Mrs Paul would have followed the doctors' recommendations. Had Dr Day and Professor Morgan recommended clipping in 2003 - as I have found both probably would - Mrs Paul would have acted on that recommendation and undergone that procedure. 52In doing so, she would have accepted the associated risks of intra-procedural rupture (5-10%) and consequential stroke (5%). The probabilities, however, were overwhelmingly against those risks materialising. Had the Plaintiff's aneurysm been subject either to clipping or coiling on any other occasion, including in 2003 consequent upon a timely diagnosis by the Defendant, then according to the agreed risk statistics agreed by the experts, to which I have referred, it is much more likely than not in respect of each other occasion taken individually, to the extent of 90% or more, that there would have been no intra-procedural rupture; and, to the extent of more than 99%, that even if there were a rupture it would not have caused a stroke and the injuries that the plaintiff in fact sustained on 8 March 2006. 53On the probabilities, therefore, but for Dr Cooke's negligence, the aneurysm would have been obliterated by clipping in 2003, without rupture or stroke. This conclusion reflects the majority reasoning in Chappel v Hart, 242, [20] (Gaudron J).

What in fact happened? 54The relevant state of affairs after Dr Cooke's negligent omission was that, for the ensuing three years, Mrs Paul was unknowingly exposed to the foreseeable risk of spontaneous rupture of the aneurysm (which did not materialise); that the aneurysm was belatedly diagnosed as a result of the referral by Dr Coleman; and that as a result, Mrs Paul underwent surgical treatment for the aneurysm in 2006 in the course of which it ruptured, causing a stroke, and Mrs Paul thereby suffered harm.

Conclusion - factual causation is established 55Chappel v Hart dictates that the correct comparison in this case is between having the operation on the occasion on which it took place, and having it on an occasion in 2003. That comparison results in the conclusion that, on the probabilities, had Dr Cooke diagnosed the aneurysm in 2003, Mrs Paul would have had it treated by clipping, and the aneurysm would have been obliterated without rupturing, and Mrs Paul would not have suffered the stroke and the consequent injuries and disabilities that now afflict her. 56Factual causation is therefore established.

Scope of liability 57The "scope of liability" inquiry under ss 5D(1)(b) and 5D(4) involves a policy judgment as to whether it is appropriate, having regard to the relevant circumstances, for the scope of the negligent person's liability to extend to the harm in question, and for this purpose the court must consider, inter alia, whether or not and why responsibility for the harm should be imposed on the negligent party. However, the principles developed by the common law continue to inform determination of causation, albeit within the statutory framework [Ruddock v Taylor, 286 [89] (Ipp JA); cf Zanner v Zanner [2010] NSWCA 343, [8] - [12]; (2010) 79 NSWLR 702 (Allsop P: there is no indication that the application of common sense is foreign to s 5D)]. In Ruddock v Taylor, Ipp JA said: [87] The second aspect concerns "the 'appropriate' scope of liability for the consequences of tortious conduct" (Stapleton, op cit, at 411). In other words, the ultimate question to be answered when addressing the second aspect is a normative one, namely, whether the defendant ought to be held liable to pay damages for that harm. This inquiry may involve normative issues of a general kind, or issues such as whether the so-called evidentiary gap should be bridged (in the sense explained in Bonnington Castings Ltd v Wardlaw [1956] AC 613), whether the defendant materially increased the risk (in the sense explained in Fairchild v Glenhaven Funeral Services Ltd [2003] 1 AC 32), and whether the damage claimed is too remote. 58In Zanner v Zanner, Allsop P referred to other considerations that may be relevant to the scope of liability inquiry: [6] The Ipp Report recognised, through a non-exhaustive discussion of the common law, the various kinds of considerations that might make up the value judgments or normative considerations under s 5D(1)(b) or s 5D(2) and s 5D(4): causal overdetermination with results attributable to more than one sufficient condition (for further discussion of this issue see H L A Hart and A M Honoré, Causation in the Law, (2nd Ed, 1985, Clarendon) at 111-117, 122-125, 128-129 and 235-253); intervening causes; the cumulative operation of two or more factors to cause indivisible harm and material contribution; other expressions of material contribution of joint and concurrent tortfeasors; the place of increase in risk; foreseeability; the state of the plaintiff to be taken as found; the place of sheer coincidence; the importance of the relevant rule of responsibility: see generally D Villa, Annotated Civil Liability Act 2002 (NSW) (2004, Lawbook Co) at 46-62. The Report stated that for the resolution of individual cases, there can only be a case by case approach, rather than by application of detailed rules or principles.

59In Wallace v Kam [2012] NSWCA 82, Allsop P said that in order for a conclusion under s 5D(1)(b) that the scope of liability should not extend, there needs to be a conclusion of the tenuousness of the factual link, or some limitation by reference to the rule of responsibility involved.

The relevant rule of responsibility 60Analysis of causation in this context is influenced by the purpose for which the question is being asked, and the "rule by which responsibility is being attributed" [Environment Agency v Empress Car Co (Abertillery) Ltd [1999] 2 AC 22 (Lord Hoffmann); see also Chappel v Hart, 256 [63]-[64] (Gummow J); Henville v Walker [2001] HCA 52, [98]-[99]; (2001) 206 CLR 459, 491; Allianz Australia Insurance Ltd v GSF Australia [2005] HCA 26 [96]-[97]; (2005) 221 CLR 568; Travel Compensation Fund v Tambree [2005] HCA 69 [45]; (2005) 224 CLR 627 (Gummow and Hayne JJ)]. As appears from the cases referred to immediately below, the imposition of a duty of care in a particular context may reflect a particular purpose, with the consequence that harm which would not have been occasioned but for a breach is nonetheless regarded as being outside the scope of liability for the breach. In Henville v Walker, McHugh J (at 491-2) gave the following illustrations: [102] Thus in Gorris v Scott (1874) LR 9 Ex 125, in the course of a voyage on the defendant's ship, the Plaintiff's sheep were washed overboard because the defendant neglected his statutory duty to provide pens on the deck of the ship. The action was dismissed because the statute was aimed at preventing disease and was not directed to the events that had happened. Thus in spite of the existence of a breach of duty that resulted in damage to the Plaintiff, there was no relevant causal connection because the damage was outside the contemplation of the statute. Similarly, in Close v Steel Co of Wales Ltd [1962] AC 367, the defendant, in breach of its duty, had failed to fence a dangerous drilling machine. The plaintiff was injured when the drill bit fragmented. His action failed because the House of Lords held that the duty to fence was limited to keeping the worker from coming into contact with the dangerous machinery and did not extend to protecting the worker from injury caused by ejected pieces of the machine. 61Similarly, in Banque Bruxelles Lambert SA v Eagle Star Insurance Co Ltd [1997] AC 191, Lord Hoffmann gave the oft-quoted mountaineer example (at 213): A mountaineer about to undertake a difficult climb is concerned about the fitness of his knee. He goes to a doctor who negligently makes a superficial examination and pronounces the knee fit. The climber goes on the expedition, which he would not have undertaken if the doctor had told him the true state of his knee. He suffers an injury which is an entirely foreseeable consequence of mountaineering but has nothing to do with his knee. 62And in Chappel v Hart, Gummow J said (at [66]): It is true that in some cases of a failure to warn by a medical practitioner an application of the "but for" test without qualification could lead to absurd or unjust results. Such would have been the situation if, for example, instead of suffering damage to her laryngeal nerve, Mrs Hart had been injured through the misapplication of anaesthetic. While it would still be open to conclude that, but for Dr Chappel's failure to warn her of the possibility of damage to her voice, she would not have opted for the operation at that time and would not have been injured by the anaesthetic, the law would not conclude that the failure to warn of the risk of injury to the laryngeal nerve caused the injury resulting from the anaesthetic. 63This approach was applied recently, in more complicated factual circumstances, by the Court of Appeal in Wallace v Kam, in which the appellant had undergone fusion to alleviate pain caused by an intervertebral disc protrusion in his lumbar spine, following which he suffered bilateral femoral neurapraxia (local nerve damage) to the thighs. The appellant sued the respondent neurosurgeon for damages in respect of a failure to warn of the material risks of the operation, namely, the risk of bilateral femoral neurapraxia (which materialised), and a 5 per cent risk of paralysis (which did not materialise). The trial judge held that the respondent breached his duty of care to the appellant by failing to warn of the material risk of bilateral femoral neurapraxia, but that the appellant would not have declined the surgery if warned of that risk. His Honour did not make a finding of whether the 5 per cent risk of paralysis was a material risk that the respondent was under a duty to disclose to the appellant, nor whether he would have declined the operation if warned of that risk, treating it as irrelevant because it did not materialise. The Court of Appeal (Allsop P and Basten JA, Beazley JA dissenting) upheld, albeit by different routes, the trial judge's judgment. Allsop P (at [12]-[14]), assuming that the appellant if warned of the risk of paralysis would not have undergone the operation, concluded that the relevant duty and the rule of responsibility was to protect the patient from harm from material inherent risks that were unacceptable to him, and (at [18]-[19], [23]) that where the risks could be seen as separate and distinct, recovery was limited to risks coming home that were material and should have been disclosed and were not acceptable to the patient. Basten JA (at [173]) was of the view that as a matter of principle, if the purpose of requiring payment of compensation was to require the defendant to bear the cost of the harm eventuating from his or her negligent conduct, it was far from clear why that burden should be imposed in circumstances where the harm could only have arisen from breach of another element of the duty. 64As the Plaintiff submits, diagnosis is an important aspect of medical care. Its importance lies chiefly in the fact that the correct identification of an injury or illness affecting a patient is (at least usually) a necessary precondition to its effective treatment and relief. Undiagnosed, a patient will not be provided the treatment appropriate for the remediation or relief of the condition, but will continue to suffer its adverse affects that might otherwise be relieved, and the condition may deteriorate. The reason for requiring the exercise of care in connection with diagnosis is to protect the patient from harm from illness or injury that can be avoided or alleviated by treatment. Thus, where a patient suffers ongoing harm from an illness or injury that would have been relieved by treatment following a prompt diagnosis, that is harm of the kind from which the rule of responsibility was intended to protect the patient. If, as a result of a failure to diagnose it, a progressive condition deteriorates in a way that reduces the plaintiff's prospects of a cure, the loss of the chance of a cure is harm of that kind. Where a condition that would have been cured following a prompt diagnosis deteriorates so that the patient requires additional treatment that would not otherwise have been required, the necessity to undergo that additional treatment is also harm of the kind against which the rule was intended to protect. And, in conformity with Mahony v Kruschich, responsibility would extend to harm from complications arising in the course of that additional treatment. 65However, diagnosis is a precursor to treatment. Such treatment will usually carry some risks. Harm from the very treatment that prompt and proper diagnosis was intended to enable is not harm of the kind against which the relevant rule of resposibility was intended to protect a patient; to the contrary, it arises from performance of the duty to diagnose, rather than from breach of it. 66The Plaintiff argued that the duty to diagnose is analogous to the duty to warn of material risks (of the type discussed in Rogers v Whitaker [1992] HCA 58; (1992) 175 CLR 479), in that both concern the right of a patient to know the condition from which they are suffering, the material risks involved in undergoing or foregoing certain treatment for that condition, and the patient's right to decide for himself or herself whether to submit to that treatment [cf Chappel v Hart, 256-7 [65] (Gummow J)]. But this is not an accurate characterisation of the rationale of the duty to diagnose, even though its performance will typically result in the patient being enabled to make decisions about treatment. In failure to warn cases, breach of the duty results in the patient undergoing a procedure and incurring its associated unacceptable risks; in a failure to diagnose case, breach of the duty results in a condition not being discovered and treated, so that the condition persists and potentially deteriorates, continuing to cause harm that could otherwise be avoided or becoming more difficult to treat in the future. Whereas the rationale of the duty to warn (as explained by Allsop P in Wallace v Kam) is to protect the patient from harm from material inherent risks that are unacceptable, the rationale of the duty in connection with diagnosis (as explained above) is to protect the patient from harm from illness or injury that can be avoided or alleviated by treatment. Unlike the duty to warn, its purpose is not truly to enable a patient to make an informed choice about treatment or to submit to what otherwise would be an assault; rather, it is to enable the appropriate treatments to be identified. 67The importance of the duty of care in the diagnosis of suspected aneurysms, in particular by diagnostic radiologists, is undoubted - not least because of the high mortality rate associated with spontaneous rupture. That duty serves to enable an aneurysm, once diagnosed, to be treated, in particular to remove the risk that it will rupture spontaneously. Harm from a spontaneous rupture which such treatment following prompt diagnosis would have avoided is harm of the kind from which the relevant duty of care is intended to protect the patient. However, the very treatment that diagnosis would enable - whether clipping or coiling - itself carries risks, including of intra-procedural rupture. Harm occasioned by the materialisation of those risks is not harm of the kind from which the relevant rule of responsibility is intended to protect the patient; to the contrary, it is harm to the risk of which the patient is exposed by treatment consequent on performance of the duty. 68In this case, the purpose of Dr Cooke's duty to make a timely diagnosis was to enable appropriate treatment. The outcome of a timely diagnosis would always have been, not avoiding a procedure, but undergoing one - either coiling as Mrs Paul later chose, with appropriate expert advice, in 2006, or clipping, as she would have chosen in 2003, each with their own risks of intra-procedural rupture. Accordingly, the harm suffered by Mrs Paul was not harm of the kind from which the relevant rule of responsibility was intended to protect her.

Foreseeability 69The Plaintiff submitted that it did not matter whether the rupture occurred during angiography, an operative procedure, or while talking on a telephone, playing netball or driving a car: rupture and stroke were foreseeable consequences of leaving Mrs Paul's condition undiagnosed and untreated, and the fact that the particular course of events involved coiling to fix the problem should not mean that Mrs Paul fails. Two examples were advanced to illuminate this argument, but the answers tend to confirm the opposite. 70The first was that if Mrs Paul had suffered rupture and stroke while driving a car, she would obviously have been able to recover; so, it was asked, why should there be a different outcome, just because the rupture occurred during surgery? The answer is that in the first case, driving the car did no more than provide the occasion for a spontaneous rupture that would have been avoided by timely diagnosis and treatment, whereas in the latter case the treatment - which was a consequence of diagnosis whenever made, not of failure to diagnose - was not the mere occasion but the immediate cause of an intra-procedural rupture. 71The second was that it was said that Mrs Paul's aneurysm may not have been diagnosed for a further 15 years, by which time it may have grown in diameter and the walls become weaker, such that the risk of rupture during surgery would then have increased, and if rupture did occur, then there could be no question that the defendant's breach caused the rupture and stroke; so, it was asked, why should the outcome be different just because (fortuitously for the defendant) the diagnosis was made three years later in 2006 rather than 15 years later? But assuming that liability would be imposed in the hypothetical case, the answer is that in that case, the delay in diagnosis would have resulted in an increase in the propensity of the aneurysm to intra-procedural rupture, so that there would be a clear association between delay in diagnosis and risk of intra-procedural rupture; whereas in the actual case, in the absence of any change in the characteristics of the aneurysm, there is no such association. 72In fact, in the context of this case, consideration of foreseeability highlights the absence of causal connection between failure to make a diagnosis and the harm suffered by Mrs Paul. Spontaneous rupture (with its sequelae) was plainly a foreseeable risk of failing to make a diagnosis. But intra-procedural rupture was a foreseeable risk of treatment associated with making a diagnosis, regardless of when the diagnosis was made - not with failing to make a diagnosis. If it be said that it was foreseeable that there might be an intra-procedural rupture in an operation, years later, occasioned by a delayed diagnosis, it was equally foreseeable that there might be such a rupture in the course of an operation following a timely diagnosis. Intra-procedural rupture was a risk associated with undergoing treatment once the correct diagnosis was made, whenever it was made; not from failing to make a diagnosis. 73The Plaintiff submitted - with reference to such cases as Mahony v Kruschich, Reeves v Commissioner of Police [2000] 1 AC 360, and Stephens & Dick v Giovenco [2011] NSWCA 53 - that surgical treatment such as that involved in Dr Parkinson's coiling procedure was a foreseen and accepted consequence of the diagnosis, such that its complications should be regarded as within Dr Cooke's responsibility, and not a novus actus interveniens. However, this misses the point. It is true that such a procedure was a foreseeable consequence of making the correct diagnosis - but that is a consequence of performance, not of breach, of the relevant duty. It was not a foreseeable consequence of failing to make the diagnosis. Dr Cooke's negligence did not create, or increase, Mrs Paul's need for the procedure, which arose from her having the aneurysm. Unlike the negligent driver who injures a pedestrian, his failure to diagnose did not create the need for subsequent medical treatment. Unlike the doctor who fails to diagnose a cancer, his negligence did not aggravate the patient's requirement for surgery. 74Thus I reject the submission that it does not matter, from the causation perspective, that it was an intra-procedural and not a spontaneous rupture. The exposure to the risk of intra-procedural rupture had nothing to do with Dr Cooke's failure to diagnose the aneurysm. It was a consequence of the aneurysm being diagnosed, whenever it was diagnosed. Ironically, had the aneurysm remained undiagnosed and had Mrs Paul not come to surgery in 2006, it may never have ruptured but remained asymptomatic, as it had for the last three years. It was the operative intervention consequent upon diagnosis of the aneurysm, not the failure to diagnose it, that caused the rupture.

Causative irrelevance of delay in diagnosis 75This leads to a further reason for denying a causal association between the delay in diagnosis and the intra-procedural rupture. In many delayed diagnosis cases, there is a clear relationship between the delay and the harm. That is because the patient suffers ongoing adverse effects from an untreated illness or injury while it remains undiagnosed, or the patient's condition deteriorates and treatment becomes more difficult while it remains undiagnosed (such as the delayed diagnosis of cancers). In those cases, the relationship is manifest: the longer the delay, the greater the harm. 76In this case, however, while as a result of Dr Cooke's breach of duty, Mrs Paul did not obtain treatment, and was thus exposed to the ongoing risk of spontaneous rupture, that risk fortunately did not materialise, and the passage of time did not make treatment of her aneurysm any more difficult - to the contrary, it saw the development or evolution of additional procedures, in particular coiling, which if anything improved the treatment options. 77At its essence, the Plaintiff's argument is that causation is nonetheless established because, if the procedure (whether coiling or clipping) had been performed on an earlier occasion, then in all likelihood there would have been no rupture and stroke. However, as the Plaintiff accepted in the course of argument, this would apply equally if the procedure were performed on a later occasion. Thus, on the same analysis that supports a finding of factual causation, further delay would also, on the probabilities, have seen her avoid her injuries and disabilities: had she come to surgery on any other occasion - after as well as before 8 March 2006 - she would probably not have had a rupture and stroke. Once it is appreciated that the argument applies equally in respect of a procedure performed later, as well as earlier, than when it was actually done in 2006, it becomes apparent that the delay in diagnosis has no meaningful causal relationship to the harm suffered by Mrs Paul. That the risk would (on the probabilities) have been avoided, whether the delay was longer or shorter than in fact it was, is a powerful indicator that delay in making the diagnosis was not causally related to the harm. This demonstrates that the failure to make a timely diagnosis was not related - except in the barest "but for" sense - to the catastrophe. In no meaningful or commonsense way did the delay in diagnosis here cause the intra-operative rupture. 78This is distinguishable from the failure to warn cases, discussed below, where liability has been imposed on the basis that had the patient undergone the procedure on any different occasion the relevant risk would probably not have materialised. As is elaborated below, this "different occasion" argument establishes only the "but for" element of the test; in failure to warn cases the scope of liability extends to such cases because the relevant risk that materialises is one which - because of the surgeon's failure to warn of it - the patient has not agreed to accept.

The scope of the risk 79In March v Stramare, McHugh J outlined an approach to causation analogous to that required by s 5D - as Allsop P has observed, in Zanner v Zanner (at [5]). McHugh J said (at 235): One such approach, and the one I favour, is the "scope of the risk" test which has much support among academic writers as well as the support of Denning LJ in Roe v Minister of Health [1954] 2 QB 66 at 85, where his Lordship said: Starting with the proposition that a negligent person should be liable, within reason, for the consequences of his conduct, the extent of his liability is to be found by asking the one question: Is the consequence fairly to be regarded as within the risk created by the negligence? If so, the negligent person is liable for it: but otherwise not (my emphasis). Damage will be a consequence of the risk if it is the kind of damage which should have been reasonably foreseen. However, the precise damage need not have been foreseen. It is sufficient if damage of the kind which occurred could have been foreseen in a general way: Hughes v Lord Advocate [1963] AC 837. But the "scope of the risk" test enables more than foreseeability of damage to be considered. As Fleming points out (The Law of Torts, 7th ed, p 193), it also enables allowance to: ... be made to such other pertinent factors as the purpose of the legal rule violated by the defendant, analogies drawn from accepted patterns of past decisions, general community notions regarding the allocation of 'blame' as well as supervening considerations of judicial policy bearing on accident prevention, loss distribution and insurance. 80Dr Cooke's negligence created a risk, which could otherwise have been avoided, that Mrs Paul's aneurysm would rupture spontaneously and cause harm. But Dr Cooke's negligence did not create the risk of intra-procedural rupture: that risk was one associated with the necessity for treatment once the aneurysm was diagnosed, whenever it was diagnosed. The plaintiff submitted that the longer the aneurysm remained in situ, the longer she was exposed to the risk of rupture. However, that proposition elides spontaneous rupture with intra-operative rupture. It is true that the delayed diagnosis increased the plaintiff's exposure to spontaneous rupture and, had the rupture been spontaneous, causation would have been established. But it did not increase the risk of intra-operative rupture, which would have been incurred whenever the diagnosis was made and the procedure was performed - in 2003, in 2006, or later. 81The plaintiff submitted that timely diagnosis would have "deflected" her from the course that eventuated - described as "ignorantly persisting with the aneurysm, when otherwise she would have had it obliterated" - because she would have had treatment earlier. But in the events that transpired, "persisting" with aneurysm itself had no consequences; it was the treatment for it that brought the consequences, and that treatment would have carried the risk of those consequences whether it took place in 2003 or 2006. The Plaintiff submits that the Defendant's negligence did not merely postpone the time at which Mrs Paul underwent remedial surgery, but that with earlier diagnosis, the risk of stroke would have been eliminated. This is not correct: with earlier diagnosis, the risk would not have been eliminated: it would have been run - albeit on another, earlier occasion. 82Accordingly, the delay in diagnosis neither created nor materially increased the risks of intra-procedural rupture, which risks Mrs Paul had to encounter whenever she underwent treatment for the aneurysm. The harm suffered by Mrs Paul in the course of the treatment of the aneurysm in 2006 cannot fairly or meaningfully be regarded as within the risk created by Dr Cooke's failure to diagnose the aneurysm in 2003.

No relevant Increase in risk from different procedure 83This conclusion is not affected by the circumstance that, based upon the risk statistics agreed by the experts, it can mathematically be deduced that the risk of stroke associated with rupture in the context of clipping in 2003 was 0.375% (7.5% x 5%), whereas the risk of stroke associated with rupture in the context of coiling in 2006 was 0.75% (1.5% x 50%). 84First, the differences are theoretical, and not material. In either case, the risk was less than one percent, and "hypothetical and problematic considerations" of this kind ought not be decisive in this field [cf Gummow J in Chappel v Hart, [81]]. The correct approach, which I have adopted for the "factual causation" analysis, is that on the probabilities, had Mrs Paul undergone either procedure in 2003, she would not have had a rupture nor incurred harm. But while conclusive of factual causation, that is not determinative of the "scope of liability". 85More importantly, Dr Cooke's breach of duty was not responsible for Mrs Paul's decision to prefer coiling to clipping in 2006. Clipping remained as available in 2006 as it had been in 2003. What had changed was that experience of and developments in coiling techniques had made coiling increasingly attractive and popular. Mrs Paul received extensive advice from her treating doctors as to her treatment options in 2006: she had had the alternative treatment options and their respective risks and benefits explained to her at least once (and perhaps twice) by Dr Day, twice by Dr Parkinson, and once again by a registrar in the hospital on 6 March 2006. With that information, albeit strongly influenced by their advice, she freely and voluntarily selected endovascular coiling as preferable. 86If anything, the delay occasioned by Dr Cooke's omission meant that Mrs Paul had available to her an additional treatment option (coiling) that was not previously so readily available, which option was in many respects a more attractive one, albeit with some different advantages and disadvantages to the other option (clipping). Clipping was still available. Where advances in medicine during the period while her aneurysm remained undiagnosed resulted in Mrs Cooke having a wider range of treatment options available, and she chose for sound reasons and on appropriate advice an option that was in many ways more attractive than the one she would have chosen in 2003, the fact that a particular risk of the chosen option that was less likely in the alternative option materialised and caused harm is not fairly or logically to be seen as attributable in any but the barest "but for" sense to the delayed diagnosis.

The failure to warn cases 87The Plaintiff relies on the reasoning in two leading failure to warn cases - Chappel v Hart in the High Court of Australia, and Chester v Afshar [2005] 1 AC 134 in the House of Lords - as supporting a conclusion that causation is established in her case. 88In Chappel v Hart, Dr Chappel had failed to warn Mrs Hart of a very small but inherent risk of perforation of the oesophagus and infection associated with throat surgery that he performed on her. This risk had been the subject of a specific inquiry by Mrs Hart, and had she known of it, she would not have had the surgery on that occasion, but would have sought out the most experienced surgeon in the field. The risk materialized. By a majority of three to two, the High Court held that Dr Chappel's negligence was a cause of the harm suffered by Mrs Hart, notwithstanding that the risk was inherent in the procedure and that she would have been exposed to that risk even if she had received an appropriate warning from Dr Chappel and the surgery had been performed at a later time by a different surgeon. 89The majority was constituted by Gaudron, Gummow and Kirby JJ, in separate judgments. Gaudron J (at [11]) explained that Dr Chappel's argument, that his failure to warn Mrs Hart of the risks involved was not causally related to her injuries, had two aspects: first, that as surgery was inevitable and the risk that eventuated inherent in it, she did not in fact suffer any damage; and secondly, that the harm resulted from the "random risk" of infection and her voluntary willingness to undertake that risk. Her Honour rejected (at [12]) the first, on the basis that it fallaciously assumed that the degree of risk was the same regardless of the experience of the surgeon concerned, and (more fundamentally) that it proceeded on the erroneous footing that the damage sustained was exposure to risk, not the harm that eventuated: "To say that Mrs Hart would inevitably have been exposed to risk of the harm which she suffered is not to say that she would inevitably have suffered the harm". And her Honour rejected the second (at [14]), because it treated the infection which occurred as a supervening event breaking the chain of causation which would otherwise begin with the failure to warn of that risk: "It is contrary to common sense to treat part of the very risk which called the duty into existence as a supervening event breaking the chain of causation beginning with the breach of that duty". Her Honour added that the question could also be answered by asking what would have happened if Dr Chappel had provided Mrs Hart with adequate information: "If he had, Mrs Hart would not then have undergone surgery and would not then have suffered the injuries which she did or their consequences. Thus, Dr Chappel's breach was 'still operating', or, continued to be causally significant when [those injuries were sustained]" (internal quotation marks omitted). 90Gummow J emphasised (at [67]-[68]) that "the very risk of which she should have been warned materialised"; that it was conceded that if the surgery had been performed at a different time, then in all likelihood Mrs Hart would not have suffered the random chance of injury; that the particular risk had been the subject of specific inquiry by Mrs Hart, for whom that risk was more significant than statistical; and that the injury occurred within an area of foreseeable risk. His Honour observed (at [78]) that if Dr Chappel had given Mrs Hart the requisite warning, she would not have undergone that procedure at his hands, but would have wanted the most experienced surgeon in the field, and (at [79]) that had she done so the cumulative risks that produced her injuries were so unlikely to occur as to be speculative. 91Kirby J also accepted that had Mrs Hart been properly warned, the overwhelming likelihood was that she would not in fact have been injured, and added (at [96]): It is true to say that the inherent risks of injury from rare and random causes arise in every surgical procedure. A patient, duly warned about such risks, must accept them and their consequences. Mrs Hart was ready to accept any general risks of the operation of which she was warned. However, she declined to bear the risks about which she questioned the surgeon and received no adequate response. When those risks so quickly eventuated, commonsense suggests that something more than mere coincidence or irrelevant cause has intervened. This impression is reinforced once it is accepted that Mrs Hart, if warned, would not have undergone the operation when she did. 92That passage emphasises the relationship between the requisite warning and the acceptance of risk by the patient, and identifies a causative link where a risk of which the patient was not warned (and would not have accepted) materialises. His Honour also observed (at [97]) that there would have been a reduced risk with a more experienced surgeon, such as Mrs Hart had said she would have sought out if properly advised. 93Because it preceded the Civil Liability Act, the reasoning in Chappel v Hart is not clearly segregated into consideration of "factual causation" and "scope of liability". However, the reasoning that if properly warned Mrs Hart would have undergone surgery on a different occasion and in all probability not been harmed, and that the relevant harm was actual physical harm not exposure to the risk of it, relates to factual causation (and is consistent with the approach I have adopted to factual causation in this case, above). The predominant reasoning relevant to "scope of liability" was that the risk that materialised and harmed Mrs Hart was the very risk that called the relevant duty to warn into existence - a risk of which she should have been but was not warned, and if warned would not have accepted, at least on the occasion on which it materialised. While Gaudron J (at [18]), Gummow J (at [79]) and Kirby J (at [98]-[99]) also referred to Mrs Hart's evidence that, if she had received the warning that Dr Chappel was obliged to provide to her, she would have retained the most experienced surgeon in the field to undertake the surgery, thereby lessening the risks of surgery, this was not essential to their Honour's conclusions. 94In Chester v Afshar, the plaintiff had severe back pain for which she required neurosurgery, which carried a 1-2% risk of the cauda equina syndrome, of which she was not warned. She proceeded with the surgery, and suffered the complication of cauda equina syndrome. The evidence established that cauda equina syndrome was a random and inherent risk of the surgery, which would have been the same whenever and at whoever's hand she had the operation. It was also established that she would have had the operation at some point in time, regardless of whether she was warned of the risk. The House of Lords (Lords Steyn, Hope and Walker; Lords Bingham and Hoffman dissenting) held that the plaintiff had established causation. The "but for" test was satisfied, because she would not have had the operation when she had it if the appropriate warning had been given and on the probabilities the complication would not have arisen on another occasion (at [19] (Lord Steyn), [81] (Lord Hope), [96], [98], (Lord Walker)). However, because there was no finding that, properly warned, the plaintiff would never have undergone the operation with the same risk, the defendant's failure to warn neither affected the risk nor was the effective cause of the injury so that, on conventional principles, the test of causation was not satisfied ([22]-[23] (Lord Steyn), [60]-[61], [81] (Lord Hope), [90] (Lord Walker)). Nonetheless, the appeal was dismissed, essentially on policy grounds (analogous to s 5D(2)). Lord Steyn (at [14]-[18]) referred to the nature of the correlative rights and duties of the patient and surgeon, the importance of a patient's right to an appropriate warning, and the obligation of a doctor to abstain from performing an operation without consent - which both served to avoid the occurrence of injuries the risk of which a patient was not prepared to accept, and ensured that due respect was given to the autonomy and dignity of each patient; his Lordship concluded (at [24]) that the plaintiff could not be said to have given informed consent to the surgery in the full legal sense, which justified a departure from conventional principles of causation. This reasoning treats the materialisation of a risk of which the plaintiff had not but should have been warned as outside the scope of what the plaintiff had accepted in submitting to surgery, and therefore causally connected to the negligent failure to warn of it. 95Lord Hope of Craighead said: [87] To leave the patient who would find the decision difficult without a remedy, as the normal approach to causation would indicate, would render the duty useless in the cases where it may be needed most. This would discriminate against those who cannot honestly say that they would have declined the operation once and for all if they had been warned. I would find that result unacceptable. The function of the law is to enable rights to be vindicated and to provide remedies when duties have been breached. Unless this is done the duty is a hollow one, stripped of all practical force and avoidable content. It will have lost its ability to protect the patient and thus to fulfil the only purpose which brought it into existence. On policy grounds I would therefore hold that the test of causation is satisfied in this case. The injury was intimately involved with the duty to warn. The duty was owed by the doctor who performed the surgery that Miss Chester consented to. It was the product of the very risk that she should have been warned about when she gave her consent. So I would hold that in can be regarded as having been caused, in the legal sense, by the breach of that duty. [88] ... I would hold that justice requires that Miss Chester be afforded the remedy which she seeks, as the injury which she suffered at the hands of Mr Afshar was within the scope of the very risk which he should have warned her about when he was obtaining her consent to the operation which resulted in that injury. 96Again, his Lordship's reasoning relies on the relationship between the risk that materialised and the duty to warn of it, and between the duty to warn and the patient's consent. 97Lord Walker also stressed the connection between the duty to warn and the need for consent: [93] The surgeon's duty to advise and warn his patient is closely connected with the need for the patient's consent to submit, under anaesthesia, to invasive surgery which would (in the absence of consent) be an assault. The advice is the foundation of the consent. That is why it is so important. ... In this case the surgeon failed to warn of the risk of the very calamity which occurred in the course of the operation which he performed three days later. 98His Lordship referred to the passage cited above from Kirby J's judgment in Chappel v Hart, and concluded: [101] Nevertheless there are real difficulties (especially, perhaps, for a conscientious claimant aware of the fallibility of hindsight) in a claimant asserting that (if warned of the risks) she would never in any circumstances have submitted to surgery. There would be a danger, as Lord Hope points out, of an honest claimant finding herself without a remedy in circumstances where the surgeon has failed in his professional duty, and the claimant has suffered injury directly within the scope and focus of that duty. I agree with Lord Steyn and Lord Hope that such a claimant ought not to be without a remedy ... 99Chappel v Hart and Chester v Afshar share the features that they are failure to warn cases, in which the relevant damage was the materialisation of the very risk that called into existence the duty to warn of it, and that a proper warning would have resulted in the patient not accepting that risk, at least on the occasion and at the hands of the surgeon in question - a choice of which the breach of duty deprived the patient, so that the relevant risk was outside the scope of the risk that the patient had accepted in submitting to surgery. The speeches of the law Lords - and the judgment of Kirby J in Chappel v Hart - emphasise the relationship between the requirement for consent and the duty to warn. Essentially, while the absence of "fully informed consent" in this sense does not vitiate consent so that the surgery amounts to an assault, its deficiency means that the patient has involuntarily been exposed to a risk which she would not have accepted then and there if properly warned, and which materialised. The rationale of these cases is that the risk that materialised was one to which the patient was exposed - although she was not prepared to accept it - because of the negligent failure to warn. In other words, because of the failure to warn, the patient suffered harm at the hands of the surgeon outside the scope of the risk that she was prepared to accept and to which - for the purposes of the law of negligence, though not that of trespass - her less than fully informed consent did not extend. In such circumstances, the law regards the materialisation of the relevant risk that should have been the subject of a warning and which the patient so warned would not then have accepted, as causally connected to the failure to warn. This reflects that the duty to warn serves to protect the patient from harm from material inherent risks that are unacceptable, by enabling the patient to make an informed choice as to whether to undergo the procedure at all, or on the occasion and at the hands of the surgeon in question. 100These considerations are not applicable to the duty to use reasonable care in and about diagnosis, which serves a different purpose - to protect the patient from harm from an ongoing or deteriorating illness of injury, by enabling its timely treatment. The purpose of diagnosis is to enable appropriate treatment, not to enable the patient to give fully informed consent to it; the information diagnosis provides is of the conditions from which the patient suffers that may require treatment and from which the plaintiff may suffer harm if not treated, not of inherent risks associated with the proposed treatment in order fully to inform a patient's decision whether or not to proceed. The risk that calls into existence the duty to diagnose is the risk of ongoing or deteriorating illness or injury if not treated - not the risks associated with treatment, to which diagnosis is a precursor. And there is no difficulty in a patient who suffers harm as a result of negligence in diagnosis recovering damages on normal principles of causation: if a patient suffers harm from the continuation or deterioration of an illness or injury that would have been avoided by treatment consequent on careful diagnosis, that harm will be within the scope of liability. 101Applied to the present facts, it was the risk of spontaneous rupture (which did not eventuate), as distinct from that of intra-procedural rupture, that called into existence the duty to make a timely and accurate diagnosis. The duty was to exercise reasonable care in reporting on the CT scans, so as to enable treating doctors to recommend appropriate treatment for Mrs Paul's condition. Dr Cooke had no duty to warn the plaintiff about, nor any other responsibility for, inherent risks of any treatment that might follow from making a proper diagnosis. If the aneurysm had spontaneously ruptured causing harm during the two-and-a-half year period in which it remained undiagnosed, when otherwise it would have been treated, then Dr Cooke would have been responsible: the delay in diagnosis would have made a real contribution to the harm. And if delay in diagnosis had increased the difficulty or risks of treatment by the time the diagnosis was belatedly made, Dr Cooke may well also have been liable. But there is no evidence of that here (there was a slight suggestion that there was an increased morbidity risk with age, but no evidence that this was material in the context of Mrs Paul being 2.5 years older; in any event, that must be offset against improvements in operative techniques and procedures over the same period). 102The Plaintiff submitted that Mrs Paul underwent a specific investigation, akin to the specific inquiry made by Mrs Hart in Chappel v Hart about the risks of surgery, to determine whether she had an aneurysm; that given what had happened to her twin sister, the potential consequences of having an aneurysm were all the more significant for her; and that, as the central concern of Mrs Hart in Chappel was obtaining adequate advice about the risks of surgery, so in this case the central concern of Mrs Paul was in finding out whether she had an aneurysm of the type that led to the tragic, early death of her twin sister, so that she could have treatment that would avert those consequences. So much can be accepted. But the consequences that Mrs Paul sought to avoid were those of spontaneous rupture; whereas the risk of intra-procedural rupture was inherent in either course of treatment that she might have chosen upon being diagnosed at any time. Treatment in which that risk was inherent was a consequence of the diagnosis, whenever it was made - not of failure to make a diagnosis. The risk that materialised was not the risk that founded the duty, but a risk associated with fulfilment of the duty, whenever it was fulfilled, by the making of a diagnosis.

Policy arguments 103The Plaintiff advanced a number of policy arguments to support extending liability to Mrs Paul's injuries and disabilities. Essentially, it was argued that the purposes of the rule of responsibility should be fostered by holding Dr Cooke liable in circumstances of an admitted breach of a duty, particularly because of the importance of diagnosis, both generally in medical practice, and specifically in respect of diagnostic radiology in the context of suspected berry aneurysms. The importance of diagnosis, and the duty to use reasonable care in and about it, is undoubted. But not only does it not follow that responsibility should be imposed on defendants for any subsequent harm; it would be contrary to law to do so without addressing the key question, whether the harm can properly be said to be caused by the breach. 104One way this argument was put was that it was necessary to hold Dr Cooke liable to Mrs Paul in the circumstances of this case, to reinforce the important obligation of a diagnostic radiologist to make accurate and timely diagnoses of serious conditions. However, that amounts to no more than an invitation to disregard to requirement to establish causation, in order to reinforce the importance of the duty of care. As has been observed, had Mrs Paul suffered a spontaneous rupture, that would have been within the risk created by Dr Cooke's negligence and he would have been held liable, as he may well also have been had the aneurysm changed in anatomy so as to increase the risks associated with treating it, and it ruptured intra-procedurally. But upholding the obligation to use reasonable care in and about diagnosis does not justify extending the scope of liability to the materialisation of a risk which is logically unassociated with delayed diagnosis, but attributable to the treatment to which diagnosis at any time would in any event have led. 105Another way in which the policy argument was advanced was that it was a matter of pure luck on the part of Dr Cooke that, at the time the aneurysm was diagnosed, it had not grown in size, thereby increasing the risk of rupture during coiling, and that Mrs Paul had not suffered a spontaneous rupture in the intervening three years; by not holding him responsible, the court would send a message to diagnostic radiologists and medical practitioners that good practice can be based upon luck, and that such a decision would be contrary to community expectations and the desire for an efficient, safe medical system. I do not think such a decision would convey any such message; a finding about causation says nothing about good practice. Again, this submission really amounts to no more than that a breach of duty should be compensated, notwithstanding the difficulty of establishing a causative link, because otherwise negligent defendants may escape liability by the good fortune that their breach of duty does not cause harm. This, of course, is not the law: good fortune means that many negligent acts and omissions do not cause harm, and therefore do not give rise to a remedy; that is the nature of the tort of negligence. 106Insofar as there is a theme in the speeches of the Law Lords in Chester v Afshar, to which I have referred, to the effect that the law ought to provide a remedy where a duty to warn has been breached, the House of Lords is not be taken to have overturned the requirement that in order to recover damages for negligence, causation must first be established. The common law of negligence has never simply provided "remedies when duties have been breached" [cf Lord Hope, [87]], except where it is established that the breach has caused damage. That does not mean that the duty is a hollow one; it means that damages for its breach are awarded only if there is a finding of causation. The Plaintiff's policy arguments essentially amount to an invitation to emphasise the importance of the duty of care by imposing liability, notwithstanding the difficulties in establishing causation.

Conclusion - the scope of liability does not extend to Mrs Paul's injuries 107The duty to use reasonable care in and about diagnosis serves to protect the patient from harm from an ongoing or deteriorating condition, by enabling its timely treatment. The harm that diagnosis was intended to avert - spontaneous rupture - did not eventuate. The harm suffered by Mrs Paul was not harm of the kind from which the relevant rule of responsibility was intended to protect her. While spontaneous rupture (with its sequelae) was plainly a foreseeable risk of failing to make a diagnosis, intra-procedural rupture was a foreseeable risk of treatment associated with making a diagnosis, regardless of when the diagnosis was made - not with failing to make a diagnosis. The irrelevance of the delayed diagnosis is demonstrated by the circumstance that had the delay before diagnosis been even longer so that Mrs Paul came to surgery on a later occasion, there would on the probabilities have been no rupture and harm. Intra-procedural rupture was not within the scope of the risk created by Dr Cooke's negligence. The fact that a particular risk of the treatment option selected on advice and for good reason by Mrs Paul in 2006, that was less likely in the alternative option that she would have undergone in 2003, materialised and caused harm is not fairly or logically to be seen as attributable in any but the barest "but for" sense to the delay in diagnosis. The factors that influence the "scope of liability" considerations in failure to warn cases are absent: in particular, that the risk that called the duty into existence materialised and was one to which the patient was exposed - although she was not prepared to accept it - because of the negligent failure to warn. The policy arguments raised in favour of imposing liability amount to no more than that proven breaches of duty should attract a remedy, even if no more than the barest factual causation can be established. The scope of liability does not extend to the harm suffered by Mrs Paul. 108It was put that Gummow J's statement in Chappel (at 262 [81]), that "It would, in the circumstances of the case, be unjust to absolve the medical practitioner from legal responsibility for her injuries by allowing decisive weight to hypothetical and problematic considerations of what could have happened to Mrs Hart at the hands of some other practitioner at some unspecified later date and in conditions of great variability", is germane to this case. However, I cannot accept that declining to extend the scope of liability to the materialisation in 2006 of a risk of intra-procedural rupture, caused by the procedure - a risk which would have been incurred whenever the diagnosis was made - involves giving decisive - or any - weight to such hypothetical and problematic considerations. This is not a judgment that Mrs Paul might have come to the same harm on another occasion. Rather, it is a judgment that viewed in a common-sense way, the delay in diagnosis did not cause her injuries.

Inherent risk: section 5I 109The conclusion I have reached in respect of causation renders it strictly unnecessary to resolve the Defendant's argument that he is not liable by reason that the injuries suffered by Mrs Paul were the result of the materialisation of an inherent risk of the procedure that she underwent. Nonetheless, in deference to the arguments that have been presented, and lest I be incorrect on the issue of causation, I shall address this issue. 110The Defendant invokes Civil Liability Act, s 5I, which provides as follows: 5I No liability for materialisation of inherent risk (1) A person is not liable in negligence for harm suffered by another person as a result of the materialisation of an inherent risk. (2) An inherent risk is a risk of something occurring that cannot be avoided by the exercise of reasonable care and skill. (3) This section does not operate to exclude liability in connection with a duty to warn of a risk.

The purpose and effect of s 5I 111The Defendant argued that s 5I can apply in circumstances where the defendant was not directly associated with the risk that materialized, so that that a defendant can rely on it notwithstanding that it was not his or her conduct that caused the inherent risk to materialise. The Plaintiff contended that the section provides an affirmative defence available in the event that a defendant is found to have a "liability in negligence", such that the defendant bears the onus of proof that the risk was an inherent one, which the plaintiff has assumed. The Plaintiff further contended that on the proper construction of s 5I, the question is whether a defendant is not liable in negligence for harm suffered by the plaintiff as a result of something occurring during the course of the defendant's conduct or activity which could not be avoided or minimised by the defendant's exercise of reasonable care and skill, and the risk must be one for which the plaintiff has assumed responsibility if it occurs - which requires either that it be patent or a matter of common knowledge so that awareness of it can be imputed to the plaintiff, or that it be one about which the plaintiff has been warned due to a correlative duty to warn. 112At common law, an inherent risk of a situation or activity is one that cannot be removed or avoided by the exercise of reasonable care. This was explained by Tobias JA in Wyong Shire Council v Vairy [2004] NSWCA 247, [164]; [2004] Aust Torts Rep ¶ 65,861 (at 65,892-65,901), in a passage that was quoted by Callinan and Heydon JJ in Mulligan v Coffs Harbour City Council [2005] HCA 63, [72]; (2005) 223 CLR 486: An inherent danger is a danger (or risk) attaching to a condition or activity that cannot be removed by the exercise of due care. That is, by exposing oneself to a condition or activity involving an inherent danger one has thereby become subject to the possibility of the danger crystallising. 113At common law, no liability for negligence arises out of the materialisation of an inherent risk. This is not a matter of defence, but simply the corollary of the definition of "inherent risk" as one that cannot be avoided by the exercise of reasonable care. The significance of inherent risks was in the context of duties to warn, in that the presence of an inherent risk - at least one that one not obvious - could call into being a duty to warn of that risk. 114Section 5I appears in Division 4 of Part 1A ("Assumption of Risk") of the Act, which was introduced by the (NSW) Civil Liability Amendment (Personal Responsibility) Act 2002, which implemented many of the recommendations of the Ipp Report. However, the section does not reflect any specific recommendation made by the Panel. The Ipp Report [Review of the Law of Negligence: Final Report, 2002, Commonwealth of Australia] discusses inherent risks in chapter 4, which deals with the liability of not-for-profit organisations and recreational activities: 4.15. The Panel considers that a distinction needs to be drawn between "inherent" and "obvious" risks. An inherent risk of a situation or activity is a risk that could not be removed or avoided by the exercise of reasonable care. An inherent risk may be obvious, but equally it may not be. In Rogers v Whitaker ... for example, the risk of sympathetic ophthalmia was inherent but far from obvious. This is one reason why it was so important for the doctor to tell the patient about it. Conversely, an obvious risk may be inherent, but equally it may not be. It may be a risk that could be avoided or removed by the exercise of reasonable care. This means that an obvious risk may be a risk that a person will be negligent. 4.16. The current law is that there can be no liability for negligence arising out of the materialisation of an inherent risk. This result actually follows logically from the definition of "inherent risk" as being a risk that could not be avoided by the exercise of reasonable care. On the other hand, under current law, failure to guard against an obvious risk may be negligent if the risk is not an inherent one. This makes it clear that the effect of Recommendation 11 may be to relieve of a person of liability for failure to remove or avoid a risk that could have been removed or avoided by the exercise of reasonable care on their part. In other words, Recommendation 11 may require a person to accept a risk that another person will be negligent. 4.17. The term "obvious risk" is designed to include risks that are patent or matter of common knowledge. In the opinion of the Panel, the mere fact that a risk is of low probability does not prevent it from being obvious. The Panel recommends a definition or provision embodying these points. Beyond this, the Panel considers that it would be undesirable and impractical to attempt to define obviousness, because whether or not a risk is obvious will be for the court to decide and must depend ultimately on the facts of each individual case. 115In the second reading speech on the introduction of the Civil Liability Amendment (Personal Responsibility) Bill, Premier Carr said [NSW Legislative Assembly, Parliamentary Debates (Hansard), 23 October 2002 at 5765]: The bill will also codify the current law so that there is no liability for the materialisation of inherent risks. Inherent risks are those risks that no amount of reasonable care and skill can avoid or minimise. If a person has a duty under the common law to warn of an inherent risk that is not obvious, that duty will not be affected by the bill. 116Despite its appearance in a part of the Act that is concerned with assumption of risk and creates defences, it ought not be concluded that the section was intended to work a radical change to the common law. To the contrary, the indicia are that it was not intended to do so, but merely to codify the common law. The section does not operate to extinguish liability for breaches of duty that cause harm, just because the same harm can also be caused without negligence. It does not create a defence in respect of proven negligence where the consequence is the materialisation of a risk that can also materialise without negligence. It simply restates the common law position that there is no liability in respect of a risk that materialises without negligence - except in the context of a breach of a duty to warn of such a risk. It is concerned with the particular risk and its materialisation in the instant case. Accordingly, it is not in truth a "defence" - anymore than it was at common law - but simply the corollary of the requirement that the plaintiff prove breach of duty and causation. 117One consequence of this is that no question of onus arises: the onus remains on the plaintiff to prove breach of duty and causation, and the defendant does not bear any onus of proving that a risk is "inherent". In reaching this conclusion, I have not overlooked that, in Lormine Pty Ltd v Xuereb [2006] NSWCA 200 (at [31]), the Court of Appeal held that a defendant bears the onus in relying on s 5L, and that s 5I appears analogous in its location in the Act and its structure to s 5L. However, while at first sight these similarities would suggest that the sections have a similar operation, s 5L was intended to give effect to a reform of the common law recommended by the Ipp Report, whereas, as I have endeavoured to explain, s 5I was not, but merely to codify the existing law. Moreover, as the section only operates where the occurrence could not have been avoided by reasonable care or skill, it makes no sense to say the onus is on the defendant. In a case in which it applies, the plaintiff would simply have failed to discharge the onus of proving breach of duty and causation. It is not necessary to show that the plaintiff has "assumed" the risk. Conversely, establishing that a risk that materialises is one of a kind that can occur without negligence (and in that sense is inherent) will not exonerate a defendant where its materialisation in the instant case is attributable to negligence. 118At common law, a tortfeasor whose negligence exposes a victim to an inherent risk that materialises, when there would otherwise have been no such exposure, is (subject to questions of remoteness) liable in respect of the consequences. The failure to warn cases are one illustration of this, and s 5I(3) makes clear that there was no intention to exonerate defendants who negligently failed to warn of inherent risks from the consequences. Another example is where a plaintiff undergoes medical treatment for injuries caused by a defendant's negligence and that treatment, without negligence, has complications. It is well established that a tortfeasor is liable for the non-negligent complications of medical treatment for injuries caused [Robinson v The Post Office [1974] 1 WLR 1176; [1974] 2 All ER 737; Liston v Liston (1981) 31 SASR 245; Mahoney v J Kruschich]. One would not lightly conclude that Parliament intended, sub silentio, to exonerate negligent defendants from liability for exacerbation - through non-negligent medical treatment - of injuries caused by them. In my view, the "reasonable care and skill" referred to in s 5I(2) is that of the defendant, and not that of some subsequent intervener whose intervention is occasioned by the defendant's negligence. 119Accordingly, s 5I(1) does not apply where the plaintiff would not have been exposed to the risk if the defendant had used reasonable care and skill.

Was the risk inherent? 120Section 5I(2) speaks of the risk of "something occurring" that cannot be avoided by the exercise of reasonable care and skill. It is the occurrence (not the risk of it) that must be unavoidable by exercise of reasonable care and skill. This accords with the focus of s 5I(1) being not the risk, but its materialisation. 121The relevant occurrence here was that of intra-operative rupture. The risk of such an occurrence was associated with both coiling and clipping. In the context of coiling, rupture can be caused by negligent placement of the catheter, or of the coils, or inflation of the balloon. But it can also be caused without negligence, and to that extent "cannot be avoided by the exercise of reasonable care and skill": the evidence of Dr Day, Dr Allan and Professor Stoodley was consistent, that risk of rupture of the aneurysm during that procedure was one that could not be avoided by the exercise of reasonable care and skill. 122The question is whether in this case the intra-operative rupture could have been avoided by the exercise of reasonable care and skill. There is no evidence, nor even allegation, of negligence on the part of the doctors who performed the procedure. But Dr Cooke was not responsible for the coiling procedure. His responsibility was diagnosis. If I were wrong in concluding that his negligence was not causative of Mrs Paul's damage, it would inevitably follow that the occurrence could and would have been avoided by the exercise of reasonable care and skill on his part.

Not in connection with a duty to warn of a risk 123The plaintiff submitted that Dr Cooke's liability related to a duty to warn of a risk. This was put on the basis that the Plaintiff unwittingly embarked upon a course of observation or conservative management without being aware of the risks associated with that course of conduct, because of the absence of a diagnosis; and that as the plaintiff was not warned of the risks she was facing at that time because no diagnosis was made, the defendant cannot be absolved from responsibility for what happened. 124However, there is no pleaded allegation of negligence against Dr Cooke in respect of "failure to warn". His admitted negligence is not in respect of any "failure to warn". His liability is not in connection with a duty to warn, but is in respect of a duty of care in respect of diagnosis.

Conclusion 125My conclusions may be summarised as follows. 126The circumstance that Dr Cooke's duty of care did not extend to responsibility for a procedure that may have been occasioned by his diagnosis (or lack thereof) is not of itself reason to deny that he is liable for damage done in the course of such a procedure; once breach of duty is established, the question is one of causation. Although the inquiry as to causation is influenced by the scope of the relevant duty, this is more appropriately considered under the "scope of liability" element of causation, which is a different notion from "scope of duty". 127Chappel v Hart dictates that the correct comparison in this case is between having the operation on the occasion on which it took place, and having it on an occasion in 2003. That comparison results in the conclusion that, on the probabilities, had Dr Cooke diagnosed the aneurysm in 2003, Mrs Paul would have had it treated by clipping, and the aneurysm would have been obliterated without rupturing, and Mrs Paul would not have suffered the stroke and the consequent injuries and disabilities that now afflict her. Factual causation is therefore established. 128The duty to use reasonable care in and about diagnosis serves to protect the patient from harm from an ongoing or deteriorating condition, by enabling its timely treatment. The harm that diagnosis was intended to avert - spontaneous rupture - did not eventuate. The harm suffered by Mrs Paul was not harm of the kind from which the relevant rule of responsibility was intended to protect her. While spontaneous rupture (with its sequelae) was plainly a foreseeable risk of failing to make a diagnosis, intra-procedural rupture was a foreseeable risk of treatment associated with making a diagnosis, regardless of when the diagnosis was made - not with failing to make a diagnosis. The irrelevance of the delayed diagnosis is demonstrated by the circumstance that had the delay before diagnosis been even longer, so that Mrs Paul came to surgery on a later occasion, there would on the probabilities have been no rupture and harm. Intra-procedural rupture was not within the scope of the risk created by Dr Cooke's negligence. The fact that a particular risk of the treatment option selected on advice and for good reason by Mrs Paul in 2006, that was less likely in the alternative option that she would have undergone in 2003, materialised and caused harm is not fairly or logically to be seen as attributable in any but the barest "but for" sense to the delayed diagnosis. The factors that influence the "scope of liability" considerations in failure to warn cases are absent: in particular, that the risk that called the duty into existence materialised and was one to which the patient was exposed - although she was not prepared to accept it - because of the negligent failure to warn. The policy arguments raised in favour of imposing liability amount to no more than that proven breaches of duty should attract a remedy, even if no more than the barest factual causation can be established. The scope of liability does not extend to the harm suffered by Mrs Paul. 129Section 5I does not operate to extinguish liability for breaches of duty that cause harm, just because the same harm can also be caused without negligence, but merely restates the common law position that there is no liability in respect of a risk that materialises without negligence - except in the context of a breach of a duty to warn of such a risk. It is concerned with the particular risk and its materialisation in the instant case. Accordingly, it is not in truth a "defence" - anymore than it was at common law - but simply the corollary of the requirement that the plaintiff prove breach of duty and causation. The onus remains on the plaintiff to prove breach of duty and causation, and the defendant does not bear any onus of proving that a risk is "inherent", or that the plaintiff has "assumed" the risk. The "reasonable care and skill" referred to in s 5I(2) is that of the defendant, and not that of some subsequent intervener whose intervention is occasioned by the defendant's negligence. Accordingly, s 5I(1) does not apply where the risk would not have materialised if the defendant had used reasonable care and skill. Applied to this case, if I be wrong in respect of causation, then although the coiling procedure in 2006 involved an inherent risk of rupture, which materialised, on the probabilities it would not have occurred if Dr Cooke had made a timely and accurate diagnosis: the occurrence could and would have been avoided by the exercise of reasonable care and skill on his part. 130Accordingly, save for the necessity to undergo the additional CT scans in 2006, Dr Cooke's admitted negligence was not causative of harm to Mrs Paul. 131It would apparently follow that there should be judgment for the defendant, but I will first, as requested, afford the parties an opportunity to be heard on the question of costs.

DISCLAIMER - Every effort has been made to comply with suppression orders or statutory provisions prohibiting publication that may apply to this judgment or decision. The onus remains on any person using material in the judgment or decision to ensure that the intended use of that material does not breach any such order or provision. Further enquiries may be directed to the Registry of the Court or Tribunal in which it was generated. Decision last updated: 27 July 2012