Aneurysm of the superior branch of anterior choroidal artery is very rare. We report this rare case with unique angiographic findings mimicking an internal carotid bifurcation aneurysm. A 35-year-old woman was admitted to our hospital because of severe headache. Lumbar puncture disclosed numerous red blood cells. Computed tomography revealed an enhanced circular area in the left basal cistern with moderate hydrocephalus. Cerebral angiography showed a saccular aneurysm near the left internal carotid bifurcation. During operation, the aneurysm was not found at the internal carotid bifurcation, but located deeper budding from the superior branch of the anterior choroidal artery. The aneurysm was successfullly clipped. The postoperative course was favourable without any neurological deficit. The postoperative angiogram showed that the aneurysm was clipped well with preservation of the main trunk of the anterior choroidal artery. Computed tomography of the brain did not show any infarction area, 3 months after the surgery. The uniqueness of this case is the favourable outcome after sacrificing the superior branch of the anterior choroidal artery. The role of collaterals of the anterior perforating substance is emphasized.
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