[Aplasia of the right internal carotid artery presenting with callosal hemorrhage: case report and review of the literature].

A 73-year-old woman without a history of cerebral ischemia suffered from sudden onset headache. Brain computed tomography (CT) showed intracerebral hemorrhage in the corpus callosum with intraventricular hemorrhage and thin subarachnoid hemorrhage in the basal cistern. Cerebral angiography showed narrowing of the right internal carotid artery just distal to its origin in the neck and abrupt occlusion just after branching of the ophthalmic artery with moyamoya-like vessels. The right A2 segment showed irregular dilatation and stenosis. The right middle cerebral artery was supplied from the basilar artery via the right posterior communicating artery. There was neither aneurysm nor arteriovenous malformation. Thin-slice bone-window CT of the skull base revealed hypoplasia of the right carotid canal. Aplasia of the right internal carotid artery was diagnosed. The origin of the hemorrhage was thought to be the irregularly opacified right A2 segment, which had been subjected to long-standing hemodynamic stress as collateral vessel.