Introduction: Morphological parameters of intracranial aneurysms (IA) are readily available from radiological imaging, and can possibly aid the decision of whether or not to prophylactically treat an unruptured IA. However, IA growth and rupture affects morphology, and possible morphological rupture predictors must be investigated in prerupture aneurysms. Both clinical and aneurysmal factors are known confounders of rupture risk, demanding matched studies or adjusted analyses.

Methods: In a nation-wide matched case-control study of 36 IA, we studied morphological parameters at time of diagnosis. 12 IA that later ruptured were matched 1:2 with control aneurysms that remained unruptured during a median follow-up time of 4.5 (interquartile range, 3.7-8.2) years. Cases and controls were matched by aneurysm location and diameter, and patient age and sex. Morphological parameters were automatically measured on 3D-models constructed from angiograms. We calculated morphological indices such as Size Ratio, Aspect Ratio, Inflow Angle and Non-Sphericity Index.

Results: The matching factors aneurysm location and diameter, and patient sex and age, were similar in cases and controls (P-values 1.0, .87, .81 and .80, respectively). Only Inflow Angle was statistically significantly different in cases versus controls in univariate analysis, where a flow direction more aligned with the parent artery was associated with future rupture (P = .045). Inflow Angle remained significant in multivariable analysis (P = .036). For cases and controls together, Maximal Diameter correlated with Size Ratio (R^2 = 0.55, P = <.001), but not with Inflow Angle (R^2 = 0.04, P = .24).

Conclusions: Aneurysm morphology may be of limited value in predicting future IA rupture at an early stage. A straighter Inflow Angle might predispose an aneurysm to changes that further increase risk of rupture, independent of IA diameter.

Patient Care: The study is concerned with the question of whether intracranial aneurysm rupture can be predicted at time of diagnosis, relevant for both individual patients, clinicians and researchers. This research improves neurosurgeons' understanding of possibilities and shortcomings of using morphological parameters to predict intracranial aneurysm rupture. The findings are a long-awaited aid to patient-specific management. Also, the results shows the importance of investigating rupture predictors in prerupture aneurysms, and might contribute to change the focus of future research.

Learning Objectives: By the conclusions of this sessions, participants should be able to: 1) Describe the importance of studying morphological risk factors for aneurysm rupture in prerupture aneurysms, 2) Discuss, in small groups, reasons for the discrepancies between the findings from this study and studies comparing postrupture aneurysms with other unruptured aneurysms, and 3) Describe the importance of considering both clinical and aneurysmal risk factors together when deciding whether or not to treat an intracranial aneurysm prophylactically.

References: Skodvin TO, Johnsen LH, Gjertsen O, Isaksen JG, Sorteberg A: Cerebral Aneurysm Morphology Before and After Rupture: Nationwide Case Series of 29 Aneurysms. Stroke, 2017 (STROKEAHA.116.015288)