The Significance of Persistent Trigeminal Artery

THE MEDICAL literature contains numerous references citing the coincidence of ersistent trigeminal artery and other cerebrovascular anomalies, the most commonly reported being saccular aneurysm (1–3). Other reports attempt to relate specific clinical syndromes to this morphological variant (4–7). The involution of the trigeminal artery during embryonic development is directly related to the formation of the circle of Willis. When the trigeminal artery is still present postnatally, there is usually hypoplasia or agenesis of the ipsilateral posterior communicating artery (S). Developmental saccular aneurysms are often associated with morphological variation of the circle of Willis (9), and, as one might expect, a saccular aneurysm associated with persistent trigeminal artery is most commonly located on the internal carotid artery where the posterior communicating artery would normally arise. As will be shown in this report, there is little evidence to support a relationship between persistent carotid-basilar anastomosis and any clinical neurological syndrome except when the anomalous vessel itself is involved in a disease process such as atherosclerosis. Until recent years, anomalous patterns of the vessels constituting the cerebral circulation were chiefly the concern of anatomists and pathologists (10–12). Their function and clinical significance, if any, could be suspected only at autopsy. The increasing use of arteriographic procedures, however, has disclosed the presence of such morphological variants more frequently and has aroused speculation in respect to their role in clinical disease (13–18). According to Padget (8, 9), the trigeminal artery is first seen in the 3 mm embryo at the junction of the paired aorta and the first aortic arch. When the first two aortic arches have undergone involution, the trigeminal artery is annexed by the internal carotid system. The trigeminal artery has an extremely important role during embryonic development since it is the principal source of blood supply to the hindbrain during the evolution of the vertebrobasilar arterial system. The basilar artery evolves by fusion of two parallel arterial channels designated the longitudinal neural arteries (19). During this stage of development, these vessels receive their blood supply at the cephalic ends principally from the trigeminal arteries and, to a lesser extent, at the caudal ends through the hypoglossal and first cervical segmental arteries (8, 20). Simultaneous with the fusion of the longitudinal neural arteries to form the basilar artery, the posterior communicating arteries become the principal channels in transporting blood from the internal carotid arteries to the basilar artery. If the trigeminal artery persists, however, a smaller amount of blood than normal will be carried by the ipsilateral posterior communicating artery from the internal carotid artery to the basilar artery.