%0 Journal Article %A L. Hacein-Bey %A P.N. Varelas %T Pedunculated Basilar Terminus Aneurysm with Pseudo-Septation due to Anterior Herniation through a Perforated Membrane of Liliequist %D 2009 %R 10.3174/ajnr.A1624 %J American Journal of Neuroradiology %P 1688-1690 %V 30 %N 9 %X 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. %U https://www.ajnr.org/content/ajnr/30/9/1688.full.pdf