Segmental duplication of the basilar artery with thrombosis.

Duplication or fenestration of the basilar artery, a result of an embryologic malformation, has an incidence of up to 5.3% in the general population. The most common complication of this anomaly is the formation of aneurysms. Thrombosis of a partially duplicated basilar artery developed in a 43-year-old man who complained of visual disturbances followed by seizures and coma, and who eventually died. Autopsy showed a partially organized thrombus occluding both halves of a duplicated portion of the basilar artery, old infarcts in the calcarine cortices, and a recent large infarct in the basis pontis. There was only minimal atherosclerosis of other intracranial arteries, including the vertebral arteries. Hemodynamic disturbances and turbulent blood flow at the site of fenestration may be the cause of the thrombosis that occurred in this artery.