くも膜下出血で発症し術前診断が困難であった解離性中大脳動脈瘤の1例

Dissecting Aneurysm of the Middle Cerebral Artery with Subarachnoid Hemorrhage Undetectable on Preoperative Neuroradiological Findings：Case Report

　要旨　患者は後頭・後頸部痛で発症した64歳男性。CTで左側に強いくも膜下出血が認められ，three-dimensional CT angiography（3D-CTA）と脳血管撮影から破裂左内頸動脈後交通動脈分岐部動脈瘤の術前診断で手術に臨んだが，動脈瘤と思われた病変は後交通動脈のinfundibular dilatationであった。左中大脳動脈分岐部はtrifurcationとなっておりこの部位にも動脈瘤はなかったが，M2下行枝の途中からM3に分岐するまでの部分が紡錘状に膨隆しており，近位部で青黒く変色して遠位部では赤味が強くなっていた。術中所見から今回のくも膜下出血はM2下行枝の解離性動脈瘤の破裂によるものと診断された。Retrospectiveにみた脳血管撮影でM2下行枝の狭窄が認められたが，術中所見の解離部位の紡錘状の膨隆と脳血管撮影での狭窄というdiscrepancyが自験例における解離性動脈瘤の診断において重要な点であった。

　We report a rare case of a dissecting aneurysm（DA）of the middle cerebral artery（MCA）associated with subarachnoid hemorrhage（SAH） undetectable on preoperative neuroradiological findings.

　A 64-year-old man was admitted to our hospital because of a sudden onset of occipital headache. CT scan showed SAH mainly in the basal cisterns and left sylvian fissure. Three-dimensional CT angiograms revealed a saccular aneurysmal protuberance at the left internal carotid-posterior communicating artery（IC-PC）region, whereas no abnormal findings at the M2 inferior trunk of the left MCA. Left internal carotid angiograms showed a saccular aneurysmal protuberance at the IC-PC region. So, preoperative diagnosis of a ruptured left IC-PC aneurysm was based on the above neuroradiological findings. The patient was surgically treated through the left pterional transsylvian approach. No aneurysm was observed either at the left IC-PC region or the trifurcation of the left MCA. The posterior communicating artery had severe arteriosclerotic change was observed. Aneurysmal dilatation with a dark-purplish ＆ reddish wall was detected at the M2 inferior trunk of the left MCA, which was thought to be the cause of the current SAH. To prevent bleeding, the lesion was clipped on wrapping with Bemsheets. Left internal carotid angiograms obtained 40 days after the onset revealed no occlusive findings at the M2 inferior trunk of the MCA was clipped on wrapping with Bemsheets. Retrospectively, preoperative angiograms revealed severe stenosis at the M2 inferior trunk of the MCA. The postoperative course was uneventful and the patient was discharged without neurological deficits. There has been no rebleeding nor new ischemic attack during the ten months since surgery.

　The 20 reported cases of a DA of the MCA associated with SAH with our case are reviewed and their neuroradiological and clinical features are discussed.

（Received : September 8, 2004）