Anastomosis found in the adulthood between the carotid and vertebro-basilar systems, apart from the posterior communicating artery, are extremely infrequent and are due to the persistence of vessels that joined both systems during the fetal period. This carotid-vertebrobasilar anastomosis are the trigeminal, otic, hypoglossal and proatlantal arteries. We report in this paper a case of a persistant trigeminal artery found in an adult male cadaver. In this case, it rose from the cavernous segment of the left internal carotid artery and traveled posteriorly to join the basilar artery between the origin of the anterior inferior cerebellar artery and the superior cerebellar artery, corresponding to a trigeminal artery type I according to Saltzman´s classification. Although it has low frequency of presentation, the trigeminal artery is associated with several pathologic conditions, and should be considered by the clinician and radiologist when enterpreting cerebral angiograms.
