[External carotid-basilar anastomosis: case report (author's transl)].

The occipital-vertebral anastomosis is one of the anastomotic channels between the external carotid system and the intracranial vessels. In this paper, we have reported a large, left external carotid-basilar anastomosis which was incidentally revealed in a patient with left hemiparesis due to arteriosclerotic occlusion of the right internal carotid artery. A 55-year-old man suddenly developed left hemiparesis without headache, unconsciousness or vomiting on the morning of January 15, 1973. When he was referred to our service on April 11, the noticeable neurological findings were left hemiparesis and left homonymous hemianopsia. The right carotid angiogram revealed occlusion of the internal carotid artery associated with collateral channels from the external carotid artery. Also a segment of the vertebral artery was visualized via the muscular branch of the occipital artery. In the left carotid angiogram, the posterior circulation was markedly visualized throught the left vertebral artery originating from the external carotid artery trunk. This anastomotic vessel had a large branch with constant caliber leading to the occipital fossa. But the posterior cerebral artery was directly visualized from the internal carotid artery without connection to the basilar artery. Repeated bilateral brachial angiograms revealed hypoplasis of the vertebral arteries. It was suggested that the persistent external carotid-basilar anastomosis might be constantly associated with hypoplasia or aplasia of the bilateral vertebral arteries.