後大脳動脈遠位部動脈瘤（P4 segment）の1例

Distal Posterior Cerebral Artery Aneurysm at the P4 Segment: A Case Report

Ⅰ．はじめに

　後大脳動脈瘤は全脳動脈瘤の約1%と稀である^4,16)．多くはP1，P2 segmentに発生し，P3 segment以降の動脈瘤は後大脳動脈瘤全体の約10%と報告されている^14,20)．P4 segment動脈瘤の頻度はP3 segment動脈瘤と同等かそれ以下であるため，全脳動脈瘤の0.05%以下であり非常に稀である^5,7,14)．また，P4 segment動脈瘤に対する血管内治療の報告は，われわれが渉猟し得た限りでは8例しかない^{6,9,11,13,18)}．今回，われわれは，破裂後大脳動脈遠位部（P4 segment）動脈瘤に対し液体塞栓物質で母血管閉塞を行った1例を経験したので文献的考察を含めて報告する．

　Posterior cerebral artery（PCA）aneurysms are rare, especially those at the P4 segment. We report such a case involving a 77-year-old man who suffered from a sudden-onset headache. Computed tomography showed intracerebral hemorrhage in the left occipital lobe, intraventricular hemorrhage, and subarachnoid hemorrhage at the left occipital sulcus. Magnetic resonance angiography failed to reveal any aneurysms or abnormal vessels. Because the patient had renal dysfunction, we refrained from conventional angiography. Five days after the initial onset, rebleeding occurred, and conventional angiography revealed a small（2-mm）PCA aneurysm in the left P4 segment. We performed endovascular treatment and occluded the parent artery with a liquid embolic material, n-butyl-2-cyanoacrylate. The etiology of the aneurysm was not determined. The patient did not suffer from any apparent visual field deficits and was transferred to a rehabilitation hospital. Reviewing previous reports of distal PCA aneurysms indicated that PCA aneurysms in the P4 segment have two characteristics that distinguish them from other PCA aneurysms:P4 segment aneurysms are relatively small and the resulting hematoma distribution tends to be manifest as a combination of intracerebral hemorrhage, intraventricular hemorrhage, and subarachnoid hemorrhage at the occipital sulcus. With respect to these characteristics, our case was a typical P4 segment aneurysm. In conclusion, although P4 segment aneurysms are rare, if the characteristic hematoma distribution is observed, conventional angiography should be performed to confirm a possible P4 segment aneurysm. Parent artery occlusion with a liquid embolic material may be a treatment option for selected cases.