Intracranial Aneurysm Parameters for Predicting a Future Subarachnoid Hemorrhage: A Long-Term Follow-up Study

Background: Retrospective studies have suggested that aneurysm morphology is a risk factor for subarachnoid hemorrhage (SAH).

Objective: To investigate whether various morphological indices of unruptured intracranial aneurysms (UIAs) predict a future rupture.

Methods: A total of 142 patients with UIAs diagnosed between 1956 and 1978 were followed prospectively until SAH, death, or the last contact. Morphological UIA indices from standard angiographic projections were measured at baseline and adjusted in multivariable Cox proportional hazards regression analyses for established risk factors for SAH.

Results: During a follow-up of 3064 person-years, 34 patients suffered from an aneurysm rupture. In multivariable analyses, aneurysm volume, volume-to-ostium area ratio, and the bottleneck factor separately as continuous variables predicted aneurysm rupture. All the morphological indices were higher ( P < .01) after the rupture than before. In final multivariable analyses, current smoking (adjusted hazard ratio 2.50, 95% CI 1.03-6.10, P = .044), location in the anterior communicating artery (4.28, 1.38-13.28, P = .012), age (inversely; 0.95 per year, 0.91-1.00, P = .043), and UIA diameter ≥7 mm at baseline (2.68, 1.16-6.21, P = .021) were independent risk factors for a future rupture. Aneurysm growth during the follow-up was associated with smoking ( P < .05) and SAH ( P < .001), but not with the aneurysm indices.

Conclusion: Of the morphological indices, UIA volume seems to predict a future rupture. However, as volume correlates with the maximum diameter of the aneurysm, it seems to add little to the predictive value of the maximum diameter. Retrospective studies using indices that are measured after rupture are of little value in risk prediction.