Small unruptured anterior circulation intracranial aneurysm rupture risk factors

According to the ISUIA, small (<7 mm) unruptured intracranial aneurysm rupture risk of the anterior circulation (aC) carry a neglectable 5-years rupture risk. In contrast, some studies report frequencies of more than 20% of all ruptured intracranial aneurysm being small anterior circulation intracranial aneurysm. This contradiction was addressed in this study by analyzing the rates and risk factors for rupture of small IA within the aC.

Of the institutional observational cohort in the Essen University Hospital, 1676 small anterior circulation intracranial aneurysm were included. Different demographic, clinical, laboratory and radiographic characteristics were collected. A rupture risk score was established using all independent prognostic factors. The score performance was checked using receiver operating characteristic curve analysis.

Of all registered small IA of the aC, 20.1% were ruptured. The developed SIAAC score (range: -4 to +13 points) contained five major risk factors: IA location and size, arterial hypertension, alcohol abuse, and chronic renal failure. In addition, three putative protective factors were also included in the score: hypothyroidism, dyslipidemia and peripheral arterial disease. Increasing rates of ruptured IA with increasing SIAAC scores were observed: from 0% (≤-1 points) through >50% (≥8 points), and up to 100% in patients scoring ≥12 points. The SIAAC score achieved excellent discrimination (AUCSIAAC =0.803) and performed better than the PHASES score.

Small anterior circulation intracranial aneurysm carry a considerable rupture risk. After external validation, the proposed rupture risk score might provide a basis for better decision-making regarding the treatment of Small unruptured anterior circulation intracranial aneurysm ¹⁾

The natural history of Small unruptured anterior circulation intracranial aneurysm in the European population is unclear. Therefore, the management of unruptured intracranial aneurysms <7 mm in the anterior circulation is controversial.

Methods: Between June 1999 and June 2012, 384 unruptured intracranial aneurysms of the anterior circulation <7 mm in diameter underwent conservative treatment and regular annual follow-up in the University Hospital Frankfurt. Patient- and aneurysm-specific information, as well as information on aneurysm enlargement and rupture, was entered into a prospectively conducted database.

Results: The mean follow-up duration was 48.5±37 months. Three aneurysms enlarged during the follow-up period and were treated by surgical clipping. Three aneurysms were ruptured during the follow-up period. The overall annual incidence of subarachnoid hemorrhage was 0.2% during the follow-up. In the multivariate Cox proportional hazard regression analysis, hypertension (P<0.001; hazard ratio, 2.6; 95% confidence interval, 2.1-3.3) and <50 years of age (P=0.04; hazard ratio, 1.3; 95% confidence interval, 1.01-1.7) were significant independent predictors of aneurysm rupture.

Conclusions: The present data indicate that the annual incidence of subarachnoid hemorrhage associated with small anterior circulation unruptured intracranial aneurysms is low in this single-institution prospective cohort study. The natural course varies according to arterial hypertension and patient age ²⁾.