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Small intracranial aneurysms of the anterior circulation - A negligible risk?

BACKGROUND
According to the ISUIA, small (<7 mm) unruptured intracranial aneurysms (IA) 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 IA being small IA of the aC. This contradiction was addressed in this study by analyzing the rates and risk factors for rupture of small IA within the aC.


METHODS
Of the institutional observational cohort 1676 small IA of the aC 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.


RESULTS
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.


CONCLUSIONS
Small IA of the aC 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 IA of the aC.