British Journal of Radiology (2007) 80, e314-e316
© 2007 British Institute of Radiology
doi: 10.1259/bjr/17918337
Unusual variant of persistent primitive hypoglossal artery
T Meguro, MD
K Terada, MD
N Hirotsune, MD
S Nishino, MD
and
T Asano, MD
Department of Neurological Surgery, Hiroshima City Hospital, 7-33 Motomachi, Naka-ku, Hiroshima 730-8518, Japan
Correspondence: Toshinari Meguro, MD, Department of Neurological Surgery, Hiroshima City Hospital, 7-33 Motomachi, Naka-ku, Hiroshima 730-8518, Japan. E-mail: tmeguron{at}hotmail.com
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Abstract
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Here, we present a case of an unusual variant of a persistent primitive hypoglossal artery, which was found incidentally during an examination for a hypertensive thalamic haemorrhage. The anastomotic vessel arose from the external carotid artery and joined the vertebral artery through the hypoglossal canal. The embryology of the anomaly is briefly discussed.
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Introduction
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Persistent primitive hypoglossal arteries are rare anastomotic vessels between the carotid and vertebrobasilar arteries. The hypoglossal artery usually arises as a robust branch of the internal carotid artery between the C1 and C3 level and traverses the hypoglossal canal to join the basilar artery. We present a case demonstrating an unusual variant of the hypoglossal artery arising from the external carotid artery.
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Case report
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A 60-year-old man with a history of hypertension was admitted owing to sudden onset of weakness of the right extremities and speech disturbance. A CT scan showed a small haemorrhage in the left thalamus. An angiogram was requested by a referring physician to evaluate the patient for vascular disease. A left common carotid angiogram demonstrated carotid basilar anastomosis. This anastomotic vessel arose from the left external carotid artery at the C2–C3 level and joined the vertebrobasilar artery (Figure 1
). A three-dimensional CT angiogram demonstrated that this vessel entered the skull through the hypoglossal canal and joined the left vertebral artery distally at the origin of the posterior inferior cerebellar artery (Figure 2). Bilateral vertebral arteries were hypoplastic.
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Figure 1. Left common carotid angiograms: (a) anteroposterior and (b) lateral views showing an anomalous vessel (arrows) arising from the external carotid artery to the vertebrobasilar artery.
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Figure 2. (a) Three-dimensional CT angiogram showing the anomalous vessel entering the skull through the hypoglossal canal (arrow). (b) The source image of the three-dimensional CT angiogram showing the enlarged hypoglossal canal and the vessel passing through the canal.
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Discussion
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Anastomotic vessels between the carotid and vertebrobasilar systems exist during embryological development. These arteries comprise the trigeminal, otic, hypoglossal and proatlantal arteries, in order from cephalic to caudal [1]. These embryonic vessels regress as the posterior communicating arteries develop. Ordinarily, the otic artery disappears at the fourth week of embryogenesis, followed soon after by the disappearance of the hypoglossal and trigeminal arteries. The proatlantal intersegmental artery maintains the posterior circulation until the vertebral arteries are fully developed between 7 and 8 weeks [2]. Occasionally, persistence of these vessels is noted after birth and into adult life. The most commonly found persistent fetal anastomotic artery is the trigeminal artery, followed by the hypoglossal, proatlantal and otic arteries. The persistent trigeminal artery has a reported incidence of 0.1–0.2%, whereas that for the persistent hypoglossal artery is 0.027–0.26% [3].
Among these anastomotic vessels, persistent proatlantal arteries are usually the ones associated with congenital anastomosis between the external carotid artery and the vertebrobasilar artery. The proatlantal artery originates from the external or internal carotid artery, and joins the vertebral artery, but enters the skull through the foramen magnum. Conversely, the persistent hypoglossal artery originates from the cervical part of the internal carotid artery between C1 and C2 levels, penetrates the hypoglossal canal, and joins the lower portion of the vertebrobasilar artery [4]. One of the most important factors differentiating these two anastomoses is whether the vessel enters the hypoglossal canal [5]. In the present case, the anastomotic vessels originated from the external carotid artery, passed through the hypoglossal canal, and joined the vertebral artery. This constitutes an unusual variant of the persistent hypoglossal artery.
There are only two previous reports of this kind of persistent hypoglossal artery [6, 7]. Nakamura et al [6] reported a 59-year-old man with a cerebral aneurysm associated with a hypoglossal artery; Welten et al [7] reported a 68-year-old man with atherosclerotic stenosis of the external carotid artery from which the hypoglossal artery arose. Both reports stated that recognition of the vessel was important for treatment and diagnosis, but did not mention the embryological anatomy of the hypoglossal artery arising from the external carotid artery. The ascending pharyngeal artery normally arises from the proximal external carotid artery and divides into two major trunks (pharyngeal and neuromeningeal trunks) [8, 9]. The neuromeningeal trunk branches into the hypoglossal canal. Komiyama [8] and Lasjaunias et al [10] suggested that this hypoglossal branch of the ascending pharyngeal artery is a remnant of the primitive hypoglossal artery. We speculate that failure of this connection to involute probably caused the unusual variant of the present hypoglossal artery.
Received for publication May 23, 2006.
Revision received August 16, 2006.
Accepted for publication September 15, 2006.
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References
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- Luh GY, Dean BL, Tomsick TA, Wallace RC. The persistent fetal carotid-vertebrobasilar anastomoses. AJR Am J Roentgenol 1999;172:1427–32.[Free Full Text]
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Abstract
Introduction
