Following aneurysmal subarachnoid hemorrhage, the primary goal of treatment is to exclude the vascular malformation from the intracranial circulation, while preserving the parent artery. In unruptured aneurysms, the decision whether to treat or observe the malformation is made on a case-by-case basis. In this regard, the ISUIA (International Study of Unruptured Intracranial Aneurysms) investigators suggested that aneurysm size and location were independent predictors for aneurysm rupture.1 ISUIA examined 1692 patients with cerebral aneurysms with a mean follow-up time of 4.1 years. Rupture rates differed depending on size and location, ranging from 0% in aneurysms <7 mm located in the internal carotid artery, anterior circulation, or middle cerebral artery to up to 50% in aneurysms >25 mm located in the posterior circulation. More recently, UCAS (Unruptured Cerebral Aneurysm Study) reported results similar to ISUIA. However, other evidence has contradicted these studies, with a higher percentage of small aneurysms reported among case series of ruptured intracranial aneurysms. This indicates a discrepancy between the ISUIA and UCAS data and the size of ruptured aneurysms seen in routine clinical practice.
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