[An unusual case of focal symptomatology, monoparalysis of the abducent nerve and vertebrobasilar ectasia].

Ectasia of the basilar artery is a well-defined form with a complicated clinical symptomatology. Angiography has made it possible to show that its pathogenesis springs from marked changes in the diameter and length of the artery. A case is presented in which the usual array of symptoms was replaced by homonymous diplopia only. It showed that CT can on its own provide information both for diagnosis of the specific lesion, and for assessment of changes in the bone structures, the cerebral parenchima, and the ventricular system.