[An operated case of a giant fusiform aneurysm of the middle cerebral artery with alternating radiological findings within a short period].

We report an operated case of a giant fusiform aneurysm of the middle cerebral artery (MCA). An 18-year-old man presenting with a 6-month history of severe left temporal headache was admitted to our department. On admission, MRI revealed a mass lesion measuring 45 mm in diameter in the left frontal lobe. A left carotid angiogram revealed aneurysmal dilatation and stenosis in the M2 portion of the left MCA, which was diagnosed as a giant fusiform dissecting aneurysm. An intracarotid amobarbital test (Wada test)demonstrated ischemic tolerance to occlusion of the parent artery. Spontaneous occlusion of the parent artery and obliteration of the aneurysmal lesion incidentally occurred 15 days after admission. Follow-up 3D-CT angiography revealed recurrence of the aneurysmal dilatation in the same segment of the artery 6 days after the spontaneous obliteration. The lesion was then successfully resected without revascularization. Histopathological examination revealed a pseudolumen and loss of the three-layer structure of the aneurysmal wall. The postoperative course was uneventful and the patient was discharged without neurological deficits. We present the case report and a review of the literature.