PT - JOURNAL ARTICLE AU - L. Hacein-Bey AU - P.N. Varelas TI - Pedunculated Basilar Terminus Aneurysm with Pseudo-Septation due to Anterior Herniation through a Perforated Membrane of Liliequist AID - 10.3174/ajnr.A1624 DP - 2009 Oct 01 TA - American Journal of Neuroradiology PG - 1688--1690 VI - 30 IP - 9 4099 - http://www.ajnr.org/content/30/9/1688.short 4100 - http://www.ajnr.org/content/30/9/1688.full SO - Am. J. Neuroradiol.2009 Oct 01; 30 AB - SUMMARY: Septations within cerebral arteries or aneurysms are exceedingly rare in the absence of associated fenestrations. We report an unusual unruptured pedunculated basilar apex aneurysm, with a “pseudoseptation” between the main aneurysmal sac and an anterior compartment, which was, in fact, represented by a perforation in the membrane of Liliequist, permitting anterior aneurysmal herniation into the carotid-chiasmatic cistern. The patient was successfully treated with detachable coils. This case is unusual on 2 accounts: 1) the aneurysm's appearance, and 2) the presence of a large fenestration in the membrane of Liliequist, of which anatomic features are herein reviewed.