T he management of patients with unruptured cerebral aneurysms (UA) remains controversial because of their uncertain natural history. Although estimates of the prevalence of intracranial aneurysms range from 0.5% to 6% on radiological and autopsy studies, the incidence of aneurismal subarachnoid hemorrhage (SAH) is 10/100.000 per year in the United States, leading to the conclusion that the majority of UAs do not rupture.1,2 The average risk of rupture of a UA is estimated to be between 1% and 2% per year. 3,4 The International Study of Unruptured Intracranial Aneurysms (ISUIA) reported on a retrospective and prospective multicenter study in 1998 and 2003. 5,6 In the latter, they observed that aneurysm location, size, and previous SAH were risk factors for rupture, with posterior circulation (PC) aneuryms collectively (including posterior communicating artery [PcoA] aneurysms) and aneurysms >7 mm located in the anterior circulation (AC) rupturing with at rates high enough to justify intervention. This observation seems to contradict the clinical perception that patients Background and Purpose-According to the International Study of Unruptured Intracranial Aneurysms (ISUIA), anterior circulation (AC) aneurysms of <7 mm in diameter have a minimal risk of rupture. It is general experience, however, that anterior communicating artery (AcoA) aneurysms are frequent and mostly rupture at <7 mm. The aim of the study was to assess whether AcoA aneurysms behave differently from other AC aneurysms. Methods-Information about 932 patients newly diagnosed with intracranial aneurysms between November 1, 2006, and March 31, 2012, including aneurysm status at diagnosis, its location, size, and risk factors, was collected during the multicenter @neurIST project. For each location or location and size subgroup, the odds ratio (OR) of aneurysms being ruptured at diagnosis was calculated. Results-The OR for aneurysms to be discovered ruptured was significantly higher for AcoA (OR, 3.5 [95% confidence interval, 2.6-4.5]) and posterior circulation (OR, 2.6 [95% confidence interval, 2.1-3.3]) than for AC excluding AcoA (OR, 0.5 [95% confidence interval, 0.4-0.6]). Although a threshold of 7 mm has been suggested by ISUIA as a threshold for aggressive treatment, AcoA aneurysms <7 mm were more frequently found ruptured (OR, 2.0 [95% confidence interval, 1.3-3.0]) than AC aneurysms of 7 to 12 mm diameter as defined in ISUIA. Conclusions-We found that AC aneurysms are not a homogenous group. Aneurysms between 4 and 7 mm located in AcoA or distal anterior cerebral artery present similar rupture odds to posterior circulation aneurysms. Bijlenga et al Risk of Aneurysm Rupture by Location and Size 3019commonly present with ruptured small aneurysms. Moreover, aneurysm locations were segregated only as being either AC or PC for risk assessment, raising concerns that the effects of pathophysiological mechanisms specific to individual arteries were combined reducing sensitivity to location as a risk factor. Work has since been published dem...

Background: Intracranial aneurysms (IAs) are more common in females than in males, however, there is still very limited knowledge on sex-dependent differences regarding aneurysm location, multiplicity, rupture risk, risk factors and histopathology. Methods: This prospective, consecutive cohort study examined whether IAs differ in multiplicity, location, geometry, rupture risk, risk factors and histology between sexes. Results: We included 982 patients (714 women, 268 men) totaling 1484 IAs (1056 unruptured, 397 ruptured). Three hundred sixty-three patients (36.97%) had multiple IAs, the proportion of which was significantly higher in females. In women, the ICA (40.79%) was the most frequent location for IAs, whereas in men most were found along the ACA territory (32.86%). Men were significantly more often diagnosed with ruptured aneurysms. Aneurysm geometry did not differ between sexes, however, ruptured aneurysms in men presented with a significantly larger neck diameter than unruptured ones. Regarding risk factors for aneurysm rupture, blood pressure control was more effective in women, whereas the effect of smoking status did not show clear sex-dependent differences. Histologically, wall-type classification analysis showed significantly more severe aneurysm wall types in men. Conclusion: IA prevalence in women is significantly higher than in men. Women more often present with multiple IAs whereas men were more often diagnosed with ruptured IAs. Sex-specific differences in IA location were identified whereas geometry of IAs did not differ between sexes. IAs in men showed a more severe histological wall type. Further research is needed to unravel the molecular mechanisms underlying these important sex-dependent manifestations in IAs.