[Dissecting aneurysm of the middle cerebral artery with subarachnoid hemorrhage undetectable on preoperative neuroradiological findings: case report].

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 ICPC 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.