Small ruptured cerebral aneurysms-do they rupture on formation or not?

Purpose: Of patients presenting with subarachnoid haemorrhage, most are due to rupture of a small aneurysm. It has been postulated that in most cases, these aneurysms form and rupture rapidly over a short period of time of days to weeks. We evaluated the hypothesis that such aneurysms therefore should never be discoverable as a pre-existing condition on medical imaging studies.

Methods: All patients presenting with subarachnoid haemorrhage due to a small cerebral aneurysm over an 11-year period were reviewed for prior imaging studies capable of detecting small aneurysms. In the subgroup that had such imaging studies, these were reviewed for the presence or absence of the index aneurysm.

Results: Of 851 patients presenting with subarachnoid haemorrhage over an 11-year period, 35 had prior imaging studies capable of detecting small aneurysms. In 18 out of these 35 (51%) patients, the index aneurysm was identified as a small unruptured aneurysm on these prior studies. The median time between prior imaging and aneurysm rupture was 31 months.

Conclusion: The theory that nearly all cases of subarachnoid haemorrhage due to small aneurysms occur as a result of aneurysm formation, and rupture over a short time period is incorrect. Our findings indicate that at least half of all subarachnoid haemorrhage cases arise from the population harbouring small aneurysms as a pre-existing condition.