Infundibular dilatationから発生した小動脈瘤が出血源であったくも膜下出血の1例

Rupture of a Small Aneurysm Originating from an Infundibular Dilatation―Case Report

はじめに

　後交通動脈が起始部において拡張している状態は，一般的にinfundibular dilatation（ID）と呼ばれている。そのIDに動脈瘤が発生してくも膜下出血を発症した報告例もあり^1－5），IDの経過観察の重要性が指摘されている。また各種画像診断の進歩に伴い直径2mm以下の小動脈瘤が発見されるようになったが，それらが破裂することは稀であると考えられている。今回，われわれは後交通動脈のIDに大きさが1.5mmの小動脈瘤が認められ，そこが出血源と考えられたくも膜下出血の1例を経験したので，若干の文献的考察も含めて報告する。

Abstract

　Infundibular dilatations (IDs) are funnel-shaped enlargements of the origin of cerebral arteries.　Usually IDs occur at the junction between posterior communicating artery and the internal carotid artery.　Progression from an ID of the posterior communicating artery to an aneurysm has previously been described, but it is unclear whether an ID is a pre-aneurysmal state or a normal anatomical variant.　In this study, we describe the successful treatment of a small aneurysm originating from a pre-aneurysmal ID.

　A 63-year-old man suddenly developed severe headache and consciousness disturbance and was admitted to our hospital.　CT scans revealed subarachnoid hemorrhage (SAH) mainly in the left sylvian fissure.　Three-dimensional computed tomographic angiography (3D-CTA) revealed an ID of the left posterior communicating artery.　A small aneurysm of 1.5mm in diameter was also observerd to extend posterolaterally from the wall of the ID.　In addition the left posterior communicating artery was well developed, and the angle between the left internal carotid artery and left posterior communicating artery was large.

　On the bosis of the CT and 3D-CTA findings, the small aneurysm originating from the ID was considered to be the cause of SAH.　On day 18, left pterional craniotomy was performed, and the patient underwent clipping of the small aneurysm.　The postoperative course was uneventful.

　An ID of the posterior communicating artery can develop into an aneurysm and subsequently rupture.　The development of an aneurysm from the ID may be influenced by hemodynamic stress and hypertension.　Thus patients with the pre-aneurysmal ID should be carefully followed up for a long time.

(Received: May 26,2009,Accepted: July 10,2009)