Background and purpose The difference in the relationship between the size of intracranial aneurysms (IAs) and their risk of rupture in patients with singe IAs versus those with multiple IAs is unclear. We sought to retrospectively analyze the size of ruptured IAs (RIAs) in patients with single and multiple IAs in order to study this relationship further.

Methods We retrospectively measured the size and location of RIAs in all patients who presented to our institute with an acute subarachnoid hemorrhage between 1 January 2005 and 31 December 2010. The IAs were classified by size into very small IAs or VSAs (≤3 mm), small IAs or SAs (>3 mm but ≤7 mm) and others (>7 mm).

Results 379 patients (281 with a single IA, Group 1 and 98 with multiple IAs, Group 2) with 419 treated RIAs were included in the study. VSAs and SAs constituted the majority of RIAs in both groups (33.5% and 45.2% in Group 1 and 24.6% and 50.7% in Group 2) and the mean size of the RIAs was not different between the two groups. VSAs constituted almost two-thirds of all RIAs in certain locations whereas IAs > 7 mm in size did not constitute more than a third of the RIAs at any of the arterial locations.

Conclusions The high incidence of VSAs, particularly in certain locations in both patient subgroups, suggests that current diagnostic, prognostic and therapeutic options in the management of IAs should be more tailored towards the management of these difficult-to-treat lesions.