Persistent Primitive Trigeminal Artery

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Abstract
The term “carotid-basilar anastomosis” refers individually or collectively to three presegmental vessels, i.e., the primitive acoustic (otic), the primitive trigeminal, and the primitive hypoglossal arteries. Each of these is represented bilaterally. In early embryonic life they extend from the primitive internal carotid artery to the basivertebral system or its anlagen. The acoustic and hypoglossal arteries are relatively transitory structures, and their persistence in the adult is rare. The trigeminal artery does not disappear as quickly, however, since it provides the primary means for conveying blood from the carotid to the basivertebral system. In the normal course of development the caudal division of the primitive internal carotid artery assumes this function (and in so doing becomes the posterior communicating artery). As a result, the trigeminal artery tends to atrophy and disappear. The trigeminal is by far the most common of the three types of persistent carotid-basilar anastomosis and constitutes over 85 per cent of the cases in the literature. For a more complete description of the embryogenesis of cranial vessels, the reader is directed to monographs by Padget and Streeter (1, 4). Review of the Literature The first article describing a persistent primitive trigeminal artery was published in 1844 (2). This article and most of the others published during the ensuing century appeared in the German literature. The subject was apparently of interest to the anatomist and pathologist rather than to the clinician. Clinical interest was promoted by the use of cerebral angiography. The first angiographic diagnosis was reported in 1950 (5), and the vast rnajority of subsequent reports have described angiograms rather than dissections. The reported incidence of persistent primitive trigeminal artery has varied considerably (Table I). In the literature to date there are altogether 126 cases2 to which the authors now add 5. Case Reports Case I: H. K., a 48-year-old alcoholic, was admitted after having been found on the street. He was confused, disoriented, dysphasic, and unresponsive to verbal stimuli. Motor, sensory, and cranial nerve functions were intact. All movements were slow. Flexor and extensor rigidity were noted. The patient walked with a wide-based gait. Electroencephalography revealed diffuse bilateral slowing. The impression was that of Laennec's cirrhosis with impending hepatic coma. The patient became unresponsive. Convulsions developed, alternating from right to left. Left facial paralysis was noted, and the left knee reflex was absent while the right was three plus. Hoffman's sign was positive. Angiographic description: Right carotid angiography demonstrated a persistent primitive trigeminal artery. The posterior communicating as well as both posterior cerebral and both superior cerebellar arteries were also visible. The left carotid angiogram failed to show a posterior communicating or posterior cerebral artery.

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