[Large distal anterior cerebral artery aneurysm associated with azygos anterior cerebral artery: case report].

A 51-year-old woman presented with a distal anterior cerebral artery aneurysm (DACAA) manifesting as severe headache and monoparesis of the left lower limb. Computed tomography revealed subarachnoid hemorrhage in the interhemispheric fissure, bilateral sylvian fissures, and basal cistern, and a hematoma in the supracallosal region. Angiography showed a large aneurysm (23 x 18 mm) located on the distal end of the azygos anterior cerebral artery (azygos ACA) at the supracallosal portion. T2-weighted magnetic resonance imaging demonstrated the hematoma as a mixed intensity mass, compressing the corpus callosum downward, and the aneurysm as a flow void anterior to the hematoma. Unilateral frontoparietal parasagittal craniotomy was performed with a horse-shoe shaped incision. The aneurysm was clipped via the interhemispheric approach, and the hematoma was aspirated. Postoperative angiography showed disappearance of the aneurysm and intact azygos ACA. The patient was discharged with mild monoparesis, paresthesia of the left lower limb and diagnostic dyspraxia. DACAA almost always arises at or near the genu of the corpus callosum and is often associated with vascular anomaly. In the literature, 22 of 26 cases of large and giant DACAA were located at or near the genu, but only 3 cases, including ours, in the supracallosal area. 11 cases were associated with azygos ACA. Therefore, hemodynamic stress caused by vascular anomaly may be involved in the formation of large or giant DACAA in contrast with cases of normal DACAA.