By Eleanor McDermid
A large study in The New England Journal of Medicine offers new data on the natural course of unruptured cerebral aneurysms.
The study involves 5720 Japanese patients with 6697 aneurysms, making it even larger than the International Study of Unruptured Intracranial Aneurysms (ISUIA), although follow up is shorter so far, at 3 years.
"This is a very valuable study, in a difficult area to get good quality information," ISUIA co-investigator Andrew Molyneux (University of Oxford, UK) told MedWire News.
The latest findings, from Akio Morita (University of Tokyo, Japan) and fellow Unruptured Cerebral Aneurysm Study of Japan investigators, generally confirm those of ISUIA. Aneurysm rupture was rare overall, with 111 aneurysms rupturing during follow up, to give an annual rate of 0.95%. However, Molyneux noted that this rate is probably higher than would be found in European populations. The rupture rate would also have been influenced by the fact that 3050 aneurysms were treated during follow up.
As in previous studies, size was an important factor. Relative to aneurysms that were 3-4 mm in size, the rupture risk increased a significant 3.35-fold in those that were 7-9 mm, 9.09-fold in those that were 10-24 mm, and 76.26-fold in those that were 25 mm or larger. These associations were independent of baseline variables, including age and smoking status.
A new finding is that aneurysms in the anterior communicating artery were about twice as likely to rupture as those in the middle cerebral artery (MCA), as were those in the posterior communicating artery. In addition, aneurysms with a daughter sac had an increased rupture risk.
Molyneux suggested that the findings may encourage more treatment of unruptured mid-size and larger aneurysms, but a more conservative approach to small MCA aneurysms. And he added that the findings "provide additional confidence for doctors in explaining life time risk/benefit ratio of treatment."
However, Molyneux said that unruptured aneurysms detected incidentally may be very different to aneurysms detected only when they rupture, as the latter could, conceivably, form and rupture over a very short space of time. "This is an area where there remains considerable uncertainty in respect of advice to patients as to what best to do."
But the low rupture rate in the context of high aneurysm prevalence (about 32,000 per 1 million adults) means randomized trials of intervention versus conservative management will need huge numbers of patients to show an effect, and it can be difficult to accrue patients to a trial where the control option is no treatment.
"Sadly, it's a field that we'll probably never get grade 1 evidence in, so observational studies is the only thing we're going to have available," said Molyneux.
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