Differences in Size Between Unruptured and Ruptured Saccular Intracranial Aneurysms by Location

Objective: It is generally accepted that larger saccular intracranial aneurysms are at greater risk to rupture. We investigated whether aneurysm location influences the effect of aneurysm size on the propensity of rupture. Methods: We reviewed patient and aneurysm characteristics in a consecutive series of patients with unruptured and ruptured aneurysms presenting to our institution between 2006 and 2018. Differences between unruptured and ruptured aneurysms at different locations were subsequently investigated. Results: A total of 766 aneurysms in 568 patients were included, with 355 and 411 unruptured and ruptured aneurysms, respectively. There were significant differences in the distribution of aneurysm location between unruptured and ruptured aneurysms (P < 0.001). The most common locations of unruptured aneurysms were the middle cerebral artery (MCA) (27.6%) and paraclinoid internal carotid artery (ICA) (25.4%), whereas the most common locations of ruptured aneurysms were the anterior communicating artery (ACOM) (34.8%) and posterior communicating artery (17.8%). Ruptured aneurysms were larger than unruptured aneurysms at all locations except at the ACOM, where there was no difference in size between unruptured and ruptured aneurysms (5.4 vs. 5.8 mm, respectively; P = 0.40). Ruptured ACOM aneurysms were also smaller than ruptured aneurysms of the paraclinoid ICA (5.8 vs. 10.3 mm; P < 0.001), MCA (5.8 vs. 8.0 mm; P = 0.021), and basilar apex (5.8 vs. 10.5 mm; P < 0.001), respectively. Conclusions: We observed no difference in size between unruptured and ruptured ACOM aneurysms, possibly suggesting a greater susceptibility for ACOM aneurysms to rupture at smaller sizes.