片側内頸動脈欠損症に合併した脳底動脈動脈瘤の2例

Basilar artery aneurysm associated with agenesis of unilateral internal carotid artery:two case reports

I．はじめに

　内頸動脈欠損症は0.01％以下と極めて稀な先天性病変であるが，比較的高率に脳動脈瘤を合併する^1）ことが知られている．これらの多くは前交通動脈に好発する^1）が，脳底動脈での発生は稀であり現在までに4例の報告^{2,17,20,24）}があるにすぎない．今回，右内頸動脈欠損症に脳底動脈動脈瘤を合併した2例を経験した．1例は前交通動脈動脈瘤の術後長期間を経て新たに発生した脳底動脈分岐部動脈瘤であり，もう1例は圧迫症状を呈し血管内手術により改善をみたがfonnow-upの血管撮影上再増大を認めた脳底動脈本幹部動脈瘤であった．このような例の報告は今だかつてなく，内頸動脈欠損という特異な血行動態がもたらす治療上考慮すべき問題点を中心に文献的考察を加え報告する．

Two patients presented with a basilar artery aneu-rysm associated with agenesis of the right internal carotid artery. In both cases, the right middle cerebral artery was supplied by the basilar artery via the en-larged right posterior communicating artery, and the right anterior cerebral artery was supplied by the left internal carotid artery via the anterior communicating artery. The first patient was a 65-year-old woman who suffered from a subarachnoid hemorrhage due to rup-ture of a basilar bifurcation aneurysm, which was de-monstrated as a “de novo” aneurysm 13 years after suc-cessful clipping of the anterior communicating artery aneurysm. Delayed surgery was planned, but she died due to recurrent hemorrhage. The second patient was a 67-year-old woman who had had a history of progres-sive left sided weakness over the previous few years. Conventional angiography and 3 dimensional CT angio-graphy showed a large aneurysm of the basilar artery trunk with a wide neck. Endovascular embolization was performed with mechanically detachable coils, and the aneurysm was incompletely occluded. The patient re-gained complete strength in the left arm after the treat-ment, but the follow-up angiography at 5 months dis-closed recanalization of the treated aneurysm, associ-ated with shift of the packed coils.

Hemodynamic stress resulting from unique collateral circulation with agenesis of the internal carotid artery may cause a predisposition to “de novo” aneurysm for-mation or recanalization of an occluded aneurysm with coils.