頭蓋外で起始した後下小脳動脈が頭蓋外窓形成部未破裂囊状脳動脈瘤を伴った1例

An Unruptured Extracranial Saccular Aneurysm, Arising from the Fenestrated Posterior Inferior Cerebellar Artery Originated from Extracranial Vertebral Artery: Case Report

後下小脳動脈遠位部の窓形成に脳動脈瘤を認めたものは稀で，脳動脈瘤および後下小脳動脈起始部が頭蓋外に位置していたものは，過去に報告はなかった。症例は71歳女性。突発性難聴の精査目的で，MRI上後下小脳動脈窓形成部に囊状未破裂脳動脈瘤を認めたが，サイズも小さく，無症候性のため経過観察している。後下小脳動脈が窓形成を含め特異的な走行を呈したことから，脳動脈瘤の成因として血行力学的ストレスとともに，血管形成不全の関与も考えられた。

Abstract

We present an extremely rare case of an extracranial saccular aneurysm arising from the proximal end of a distal fenestration in the posterior inferior cerebellar artery (PICA), with the PICA originating extra-cranially from the vertebral artery (VA).

[Case] A 71-year-old woman with hypertension, was referred to our hospital for hearing disturbance. After the incidental discovery of an unruptured aneurysm on magnetic resonance imaging, an angiography showed the aneurysm arising from the proximal end of the right distal fenestrated PICA. Both the aneurysm and the origin of the PICA were extracranial. The patient was treated conservatively because of the size and shape of the aneurysm.

[Conclusion] A literature review revealed nine reported cases of fenestrated PICAs, two of which were aneurysms with fenestrated PICAs. This present case repot is the first to describe an extracranial aneurysm in a fenestrated PICA of extracranial origin. Embryologically, PICA fenestrations may represent remnants of a plexiform arterial channel between the primitive VA and a vertebrobasilar anastomosis.