Predicting Aneurysmal Rupture Rates: Are Smaller Aneurysms Really Less Apt To Bleed and Does Morphology Matter? (S46.006)

OBJECTIVE: To investigate whether high-risk morphology occurs more frequently in ruptured intracranial aneurysms (RIA) under 7mm. BACKGROUND: An estimated 2%-5% of the general population has an intracranial aneurysm (IA) and the effects of rupture are devastating. Data from the International Study of Unruptured Intracranial Aneurysms (ISUIA) represented a low risk of rupture (0.05%/year) of aneurysms under 10 mm. The majority of RIAs treated in our center have been under 7mm, which forces one to question how best to counsel a patient with an incidentally found IA under 10mm. Aneurysmal 3D morphology is thought to be a useful predictor for risk of rupture. DESIGN/METHODS: 202 RIAs from 202 consecutive patients during 2004-2012 were evaluated by two independent neuroradiologists retrospectively using CTA for size and morphology. We used the ISUIA criteria to define size and morphology. We presumed types 1,2 and 3,4 represented low-risk and high-risk morphology, respectively. Inter-rater reliability was of concern; thus, a second evaluation with the examiners was carried out to reach consensus. Chi square analysis was used to evaluate the relationship between RIA morphology and size (under 7mm and above 7mm). Multivariable logistic regression was used to evaluate morphology as an independent predictor of size of RIA while controlling for other factors. RESULTS: RIAs under 7mm in diameter represented 53% of the 202 aneurysms evaluated. Of the RIAs under 7mm, 71% had low-risk morphology vs. 45.3% for the above 7mm group. (P CONCLUSIONS: Low-risk aneurysm morphology is found more frequently with smaller RIAs (under 7mm in diameter). Future research should include both patients with a ruptured IA and those with an unruptured IA to determine if size and morphology is related to the outcome for an aneurysm. Disclosure: Dr. Schwieterman has nothing to disclose. Dr. Terry has nothing to disclose. Dr. Markert has nothing to disclose. Dr. Ludwig has nothing to disclose.