[Early subarachnoid hemorrhage from a bacterial aneurysm of the middle cerebral artery bifurcation following cerebral infarction caused by a septic embolism: case report].

A 38-year-old left-handed male, with a past history of ventricular septal defect, presented to our hospital with complaints of sudden onset of right hemiparesis and restlessness. Computed tomography (CT) showed a hypodense area in the left insular cortex and corona radiata. The symptoms worsened on the next day, and CT demonstrated a new hypodense area in the left temporal lobe. Echocardiography showed vegetation on the mitral valve, so the patient was treated with a high dose of antibiotics under a diagnosis of infective endocarditis. Although the course was uneventful, subarachnoid hemorrhage was observed on the 4th day, which was followed by hemorrhagic infarction. Cerebral angiography revealed an aneurysm of the bifurcation of the middle cerebral artery and occlusion of the superior trunk of the M2 portion. T he aneurysmwas successfully obliterated, and histological examinationestablished the diagnosis of a bacterial aneurysm caused by septic embolism. Septic embolism originating from infectious endocarditis is likely to be followed by acute hemodynamic changes and fatal events. Therefore, the possibility of bacterial aneurysm should be considered immediately in patients with neurological deficits caused by septic embolism.