Cerebral Aneurysm Size before and after Rupture: Case Series and Literature Review.

BACKGROUND: The conclusions of the International Study of Unruptured Intracranial Aneurysms (ISUIA) demonstrating that anterior circulation aneurysms less than 7 mm in maximal diameter have a 0% risk of rupture continue to be widely cited despite discordance with the anecdotal observation that the majority of ruptured cerebral aneurysms are less than 7 mm. The leading hypothesis to reconcile this discrepancy is that cerebral aneurysms shrink after rupture. Our case series of 6 subjects adds to the scarce published literature that addresses our limited understanding of aneurysm size before and after rupture. METHODS: Our institutional database was evaluated for patients with brain vascular imaging before and after cerebral aneurysm rupture. We evaluated clinical and anatomic features as well as aneurysm dimensions using a submillimeter measurement tool with adjudication between 2 physicians. RESULTS: Among our 6 subjects who met the inclusion criteria, and even when combined with the 17 subjects published in the literature with similar information before rupture, no aneurysms decreased in size more than 2 mm. In total, 17 out of 23 aneurysms studied increased in size after rupture. CONCLUSIONS: Our data add additional evidence that unruptured aneurysms do not shrink in size after rupture. The discrepancy between the ISUIA conclusion on aneurysm size and rupture risk and what is observed anecdotally remains an area in need of additional study.