[A case of spontaneous middle cerebral artery occlusion associated with a cerebral aneurysm angiographically disappearing after STA-MCA anastomosis].

We report a case of a rapidly growing cerebral aneurysm in the basal abnormal vascular network associated with spontaneous middle cerebral artery (MCA) occlusion. The aneurysm disappeared spontaneously shortly after performing STA-MCA anastomosis. A 54-year-old female was admitted to our hospital because of repeated attacks of right hemisensory disturbance and dysarthria. CT scan and MRI images showed the infarcted focus in the left parieto-occipital lobe. Bilateral MCAs were undetectable on MRI images. Cerebral angiography revealed that the bilateral MCAs were occluded in their proximal origin with basal abnormal vascular networks. The distal MCA branches were perfused via the vascular networks. A small aneurysm was detected in the distal portion of the left Heubner's artery. There were no abnormalities in the bilateral internal carotid arteries, the anterior cerebral arteries, and the basilar artery. The follow-up angiography performed 29 days after admission revealed a growing aneurysm with a diameter of 3 mm in the distal enhanced lesion consistent with the aneurysm observed in the angiography. An STA-MCA anastomosis was performed for improvement of cerebral misery perfusion. Single photon emission tomography (SPECT) performed 9 days after the bypass operation revealed improvement of cerebral blood flow in the left parieto-occipital lobe, and her TIA attacks disappeared. The aneurysm was undetected in the cerebral angiography performed 24 days after the bypass operation. Spontaneous MCA occlusion is a rare condition of chronic cerebrovascular occlusive diseases. Diagnostic criteria of the disease includes the MCA occlusions or stenosis with basal abnormal vascular networks. Usually the phenomenon is seen unilaterally, which differs from moyamoya disease. Diagnosis must exclude diseases caused by the etiologies such as those of arteriosclerotic origin. There have been 24 reported cases of spontaneous MCA occlusion including our case. Among them, 9 cases presented cerebral aneurysm located in abnormal vascular networks, and all the reported cases presented cerebral hemorrhage at their onset. The abnormal basal vascular network may be developed as collateral vessels to supply blood to the ischemic regions in this disease. An increased hemodynamic stress in the abnormal basal vascular network may produce a true aneurysm in the distal portion of the perforating arteries. STA-MCA anastomosis reduced the TIA attacks, but also decreased the hemodynamic stress on the abnormal basal vascular network and resulted in reduction in size or thrombosis of the aneurysm. STA-MCA anastomosis can be considered effective to treat cerebral aneurysms located in vessels with increased hemodynamic stress.