破裂後大脳動脈P4部動脈瘤の1例—出血発症多発脳動脈瘤治療のpitfall

A Case of Ruptured P4 Segment Aneurysm of the Posteior Cerebral Artery : therapeutic pitfalls encountered when dealing with the multiple intracranial aneurysms

I．はじめに

　後大脳動脈瘤は椎骨脳底動脈領域の動脈瘤の約15％を占め^11），そのほとんどは，後大脳動脈起始部より後交通動脈分岐部までのP1部，および後交通動脈分岐部より中脳後縁に至るP2部に発生しており，より末梢の後頭葉脳溝内にあたるP4部にはまれ^11,19）である．今回，われわれはくも膜下出血（SAH）にて発症した破裂P4部動脈瘤症例で，合併する内頸動脈後交通動脈分岐部の未破裂動脈瘤を，破裂病変との診断のもとに急性期にclipping術を行い，術後18日目に初回血管撮影で見逃されていたP4部動脈瘤の破裂を来たした1例を経験した．本例は，動脈瘤の好発部位ではないP4部動脈瘤の再破裂が示唆され，出血発症の多発性動脈瘤の出血源同定や治療方針決定におけるpitfallと思われ，文献的考察を加え報告する．

A P4 segment aneurysm of the posterior cerebral artery has rarely been described. A case of rupturedP4 segment aneurysm, which re-ruptured after clipping procedure for unruptured internal carotid arteryaneurysm, was reported.

A 57-old-man had sudden onset of severe headache and vomiting and was transfered to our hospital. CTscan on admission showed diffuse subarachnoid hemorrhage dominantly extending to the tentorial surfaceand the occipital interhemispheric fissure. Four-vessel angiography demonstrated a right internal carotid-posterior communicating artery junction aneurysm, and its neck clipping was perfomed on day 5. Intraop-erative inspection of the whole appearance of the aneurysm was difficult because of the aneurysm existingon the ventral portion of the internal carotid artery and definite diagnosis of the bleeding source was notobtained. On day 23, he complained of severe headache and restricted vision and CT scan showed in-tracerebral hematoma in the left occipital lobe with intraventricular hemorrhage. The angiograms and CTscan on admission were reexamined, and another aneurysm on the left parieto-occipital artery (P4segment) was retrospectively identified. The ruptured P4 segment aneurysm was obliterated via the in-terhemispheric approach and the patient enjoyed an uneventful postoperative course. When a thick subarachnoid hemorrhage distributed in the occipital interhemispheric fissure, qua-drigeminal cistern, and ambient cistern is encountered, the existence of a possible P4 segment aneurysmshould be suspected. Correct initial diagnosis and definite treatment of the ruptured lesion in the acutestage is essential in dealing with SAH-patient with multiple aneurysms. When they are unruptured lesionsat a common aneurysm site, the existence of an unusually located aneurysm should not be overlooked asthe possible source responsible for symptoms.