In this article we review the recent decision of Paul v Cooke [2013] NSCA 311 which highlights the issue of factual causation and legal causation.

Material Facts

In 2003 Mrs Paul underwent an angiogram. Dr Cooke, the radiologist who reviewed the angiogram failed to identify an aneurysm.

Mrs Paul received a diagnosis that she had a berry aneurysm in the wall of her right arterial cerebral artery on 18 January 2006.

At the recommendation of her treatment providers, Mrs Paul underwent surgery to remove the aneurysm. It was agreed that the most appropriate surgical treatment for the aneurysm was through a coiling procedure.

During the surgery the aneurysm ruptured and Mrs Paul suffered permanent impairment.

Mrs Paul brought a claim against Dr Cooke for failing to diagnose the aneurysm in 2003. She argued that if the aneurysm had been diagnosed then she would have undergone surgery at that time would not have suffered the rupture in 2006.

Prior to trial the parties agreed that Dr Cooke’s failure to diagnose the aneurysm in 2003 was below an acceptable standard of care.

The risk of an aneurysm rupturing is contributed to by the aneurysm’s size and location.

If the aneurysm had been diagnosed but “remained untreated there was a 1% - 2% risk of spontaneous rupture. If it did rupture there was a 60% chance of death and a significant risk of permanent neurological deficit if she survived.”

If the aneurysm had been diagnosed in 2003 there were three courses available for treatment, all with risks:

  1. First was conservative treatment which meant monitoring the aneurysm with the view to intervening if it changed shape or size or if warning headaches occurred; or
  2. Second, a medical procedure known as clipping where a band is placed around the neck of the aneurysm in open neurosurgical operation under a general anesthetic. The associated risk of rupture during this procedure is 5% - 10%; or
  3. The third option was a procedure known as coiling. This is less invasive but had only an 80% chance of eliminating the aneurysm permanently. This is ultimately what the plaintiff underwent in 2006. If she had undergone this procedure in 2003 instead of 2006 there was still a 1% - 2% chance of the aneurysm rupturing during the coiling procedure.

Mrs Paul’s twin sister died at age 37 due to an aneurysm which had been treated conservatively. The court found that due to this Mrs Paul would not have elected conservative management of the aneurysm.

The aneurysm was diagnosed during an angiogram performed on 18 January 2006. The Court found that Mrs Paul was given accurate advice about the procedures available to her and their associated risks. She elected to undergo the coiling procedure in March of 2006.

During that procedure the aneurysm ruptured causing a hemorrhage and as a result of which Mrs Paul suffered a stroke causing paralysis of the right side. She also suffered neurological disability and cognitive impairment.

Judgment at first instance

Mrs Paul’s argument at trial and on appeal was but for the negligence of Dr Cooke her aneurysm would have been detected in 2003, she would have opted to undergo clipping which would on the balance of probabilities have eliminated the aneurysm and that Dr Cooke’s negligence caused her to be exposed to the risk of the rupture in 2006. That risk materialized and caused her damage. She further argued that had she undergone the procedure in 2003 she would not have been exposed to the same risks which materialised in 2006.”

At trial, Mrs Paul’s the case was presented on the basis that Dr Cooke was legally responsible for the adverse outcome of the operation in 2006.

The trial Judge rejected Mrs Pauls’ argument.

By the end of the trial it was common ground between the parties that:

  1. There was no physical change in the aneurysm between 2003 and 2006 which increased its propensity to rupture or altered the risks of the various options for its treatment;
  2. The risks associated with the courses available to treat the aneurysm had not changed in that 3 year period.

The primary Judge found that there was factual causation but the scope of liability requirement was not made out as there was no change in the size of the aneurysms between 2003 and 2006 and the associated risks of each procedure had not changed in that time frame. Therefore Mrs Paul failed on the issue of causation.

Dr Cooke’s defence that the harm was the materialisation of an inherent risk was also rejected.

The Court of Appeal Decision

On appeal the plaintiff’s case did not change.

It was noted by the Court of Appeal that Ms Paul’s condition pre-dated Dr Cooke’s negligent diagnosis.

The Court further noted that:

  1. The relevant risk arose after the aneurysm had been diagnosed;
  2. Dr Cooke did not create the relevant risk;
  3. The relevant risk could not be avoided by reasonable care on the part of Dr Cooke;
  4. The relevant risk was always present once Ms Paul developed an aneurysm; and
  5. The relevant risk could never materialise until it was diagnosed and Ms Paul chose to undergo surgery.

Put simply, the Court of Appeal held that whether or not Dr Cooke exercised reasonable care, Ms Paul always faced the risk of intra-operative rupture if she chose to undergo surgery. Either way, the whole of the harm suffered by Ms Paul was as a result of the materialisation of the risk in 2006 she chose to run on the operating table.

It is clear from the reasoning provided by the Court of Appeal that a plaintiff needs more than establishing breach and loss which would not have been suffered but for the breach.

That is to say, factual causation is not sufficient.

Whilst Ms Paul submitted that the duty to diagnose cannot be, and should not be, partitioned from the duty to inform because the patient’s right to know what he or she is suffering from, and to decide for himself or herself to undergo treatment, depended upon both diagnosis and warning.

However, the Court of Appeal noted that the High Court has repeatedly acknowledged the importance attributed by the common law to the patient’s right to choose, so that there is informed decision-making before undergoing medical procedures which have unavoidable risks but the central difficulty Ms Paul faced was that she was fully warned in 2006, so that common law policy was not available to support her claim based on Dr Cooke’s 2003 negligence.

The primary judge dealt with the submission that surgical treatment was the foreseeable consequence of performance of the duty, and was not a foreseeable consequence of failing to do so.

Similarly, the Court addressed the considerations that Dr Cooke would be liable if Ms Paul had suffered a stroke while driving a car, or if there had been no diagnosis for many years, such that there was an increase in the propensity to intra-procedural rupture.

Those were reasonably foreseeable consequences of the breach of duty, but they were not the harm Ms Paul suffered.

The Court of Appeal therefore confirmed the limiting principle noted recently by the High Court in Wallace v Kam1 that “the scope of liability normally does not extend beyond liability for the occurrence of such harm the risk of which it was the duty of the negligent party to exercise reasonable care and skill to avoid. It was no part of Dr Cooke’s duty to avoid the risk of intra-operative rupture.


The Court of Appeal confirmed the primary judge’s finding that it is not enough to prove factual causation - that there was a breach of duty owed and loss was suffered.

There is a need to prove the scope of that loss was within the defendant’s power to avert. In this case whilst it is acknowledged that Dr Cooke was negligent in not diagnosing the aneurysm in 2003, the outcome suffered by Mrs Paul was not within Dr Cooke’s scope of liability.

The risk of the aneurysm rupturing did not change whether Dr Cooke diagnosed the aneurysm or not, as when it was eventually diagnosed three years later the risks were the same. There was no change in the shape or size of the aneurysm between 2003 and 2006. There was also no change in the surgical intervention which could be offered to Mrs Paul and the risks associated with each procedure during that time.

In effect, if you can’t show actual breach has caused a different outcome, you have not proven causation.