Scullen T, Mathkour M, Dumont A, Glennon S, Wang A
-BACKGROUND: The cerebrovascular anatomy varies, with many associated variants and persistent channels. Many such vessels have been reported to carry an increased risk of intracranial aneurysm (IA) formation. We conducted a systematic literature review of IAs associated with variant anatomy.-METHODS: We performed a systematic review without a meta-analysis in accordance with the PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines for studies involving IA formation in patients with variant anatomy. Studies were excluded if 1) the IAs were associated with malformations; 2) the variant anatomy discussed was in the form of segment hypoplasia or aplasia; 3) the anatomical variants were discussed secondary to the intervention; 4) insufficient information had been included; or 5) they were literature reviews.-RESULTS: A total of 64 studies had met the inclusion and exclusion criteria for the final review. IA rupture was present in 91 of 131 cases (69.5%). Of the 131 IAs, 45 (34.3%) had been associated with an anomalous vessel origin or course, 43 with segmental fenestration (32.8%), 26 with a primitive persistent anasto-mosis (19.8%), and 17 with multiple or accessory vessels (12.9%). A total of 122 IAs (93.1%) had been treated with endovascular (64 of 122; 52.5%), microsurgical (57 of 122; 43.5%), or combined (1 of 122; 0.8%) methods.-CONCLUSIONS: Variant, anomalous, and persistent primitive anatomy have often been reported in association with IA formation. These lesions present with a high proportion of rupture and warrant a low threshold for treatment. Pres-ervation of perfusion is critical because such vessels developmentally exist to maintain flow.