Surg Radiol Anat (2010) 32:801–804 DOI 10.1007/s00276-010-0664-y
ANATOMIC VARIATIONS
Rare variant of persistent primitive hypoglossal artery in magnetic resonance angiography Eun Joo Lee • Hyuk Won Chang • Chul Hyun Cho • Ealmaan Kim • Sang Kwon Lee • Jung Hyuk Kwon
Received: 16 January 2010 / Accepted: 24 March 2010 / Published online: 14 April 2010 Ó Springer-Verlag 2010
Abstract We present an extremely rare case of a variant of persistent primitive hypoglossal artery, which was found incidentally in magnetic resonance angiography during an examination for dizziness. This anastomotic vessel arose from the external carotid artery (ECA), not internal carotid artery, and entered the hypoglossal canal to basilar artery. To our knowledge, this is the fourth reported case of the persistent hypoglossal artery arising from the ECA. The possible clinical implications of this anomalous vessel are discussed. Keywords Persistent hypoglossal artery Carotid-vertebrobasilar anastomoses Magnetic resonance angiography External carotid artery
Introduction Persistent primitive hypoglossal artery (PHA) is a rare embryonic carotid–basilar artery anastomosis, with a reported incidence of 0.027–0.26% [4]. Together with trigeminal, otic, and proatlantal intersegmental arteries, it represents the remnant of vascular channels’ unsuccessful E. J. Lee H. W. Chang (&) S. K. Lee J. H. Kwon Department of Radiology, Keimyung University Dongsan Medical Center, 194 Dongsan-Dong, Jung-Gu, Daegu 700-712, South Korea e-mail:
[email protected] C. H. Cho Department of Orthopaedic Surgery, Keimyung University Dongsan Medical Center, Daegu, South Korea E. Kim Department of Neurosurgery, Keimyung University Dongsan Medical Center, Daegu, South Korea
involution in human embryo. The hypoglossal artery usually arises from internal carotid artery (ICA) between the Cl and C3 levels and passes through the hypoglossal canal to join the basilar artery. We present an extremely rare case demonstrating a rare variant of the PHA from the external carotid artery (ECA).
Case report A 78-year-old man was admitted with vague dizziness for 10 days. Neurologic examination revealed no abnormality. Magnetic resonance imaging (MRI) was performed to evaluate the brain stem and cerebellum, and electronystagmography was also performed. MRI showed old lacunar infarcts in both basal ganglia. Contrast enhanced MRA indicated an anomalous vessel arising from left ECA at the C2–3 level and leading to basilar artery (Fig. 1a, b). Bilateral vertebral arteries were hypoplastic. Imaging of time of flights demonstrated that this anomalous vessel entered the skull through the hypoglossal canal (Fig. 1c). Electronystagmography showed left posterior benign paroxysmal positional vertigo. After particle repositioning, the symptom was relieved.
Discussion Anastomoses between the carotid and vertebrobasilar circulations exist during embryological development. When the embryo is 4 mm long (the Carnegie stage 11), two longitudinal neural arteries arise along the surface of the hindbrain on both sides of midline. This fusion produces basilar artery. Four arterial anastomoses: the primitive hypoglossal, trigeminal, otic, proatlantal intersegmental
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Fig. 1 a Coronal imaging of contrast enhanced MRA showing an anomalous vessel arising from ECA to the basilar artery (arrows). b Sagittal imaging of contrast enhanced MRA showing an anomalous
vessel arising from ECA to the basilar artery (arrow). c Axial MRA in three-dimensional time of flight showing enlarged left hypoglossal canal and the vessel passing through the canal (arrow)
arteries exist between primitive internal carotid and bilateral longitudinal neural arteries (Fig. 2). These anastomotic vessels were named from the cranial nerves with which
they course. When the embryo is 5–6 mm long (the Carnegie stage 13), their involution coincides with the development of the posterior communicating artery. The
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Fig. 2 Three-dimensional sketch of the embryonic carotid-vertebrobasilar anastomoses at the Carnegie stage 11. Trigeminal (T), otic (O), hypoglossal (H), and proatlantal intersegmental (P) arteries, longitudinal neural artery (LNA), primitive internal carotid arteries (ICAs), ventral aorta (VA), dorsal aorta (DA), future posterior communicating arteries (dotted lines with thick arrows)
first to regress is the otic artery, followed by the hypoglossal, trigeminal, and proatlantal intersegmental arteries. The proatlantal intersegmental artery exists for supplying blood to caudal hindbrain until 7–8 weeks, when the vertebral arteries accomplish this function. Occasionally, these anastomotic arteries remain patent and persist to adult life [13]. The trigeminal artery is most commonly found with a reported incidence of 0.1–0.2%, and the PHA is the second most with 0.027–0.26% incidence, whereas the persistent otic and proatlantal intersegmental arteries are less frequent [5]. The PHA is slightly more frequent in women and on the left side. This anastomosis was discovered by Batujeff [3]. The diagnosis of persistent hypoglossal artery is based on the following criteria revised by Brismar: (1) the artery should arise from the ICA as an extracranial branch; and (2) the artery should pass through the hypoglossal canal before joining the caudal part of the basilar artery. In addition, the persistence of primitive arteries is usually associated with compromised posterior circulation [4]. In our case, the anomalous artery arose from the ECA, but clearly fulfilled the criteria for the PHA in that this artery passed through the hypoglossal canal. Among four anastomotic vessels, persistent proatlantal artery is associated with congenital anastomosis between the ECA and the vertebrobasilar system. The proatlantal artery arises from the ECA, ICA between the C2 and C4 level or common carotid artery bifurcation, and joins the vertebral artery via the foramen magnum [8]. Entering the hypoglossal canal is the most important factor for differentiation of these two anastomotic arteries [1].
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There have been several reports similar to ours. Meguro et al. [9] reported a 60-year-old man with left thalamic hemorrhage and found an unusual variant of PHA incidentally. Nakamura et al. [11] reported a 59-year-old man with a cerebral aneurysm and also found a PHA arising from ECA. Welten et al. [14] reported a 68-year-old man with atherosclerotic stenosis of the ECA where the PHA arose. In addition, Kim et al. [6] reported another type of the variant PHA connecting the ECA and the posterior inferior cerebellar artery (PICA) with patent posterior circulation. The ascending pharyngeal artery arising from the proximal ECA divides into two trunks: pharyngeal and neuromeningeal trunks. The neuromeningeal trunk branches into the hypoglossal canal. Lasjaunias et al. [7] suggested that this hypoglossal branch of the ascending pharyngeal artery is a remnant of the PHA. Considering these reports, it is thought that the failure of this connection to involute probably caused the unusual variant of the PHA arising from the ECA. In these reports, conventional angiography was performed as a diagnostic tool, but we used only brain and carotid MRA. Although conventional angiography has been considered the standard for the evaluation of vascular structures, computed tomography angiography (CTA) or MRA are non-invasive alternatives that have some advantages. Theses afford excellent anatomic location of this anomalous vessel by showing the vessel entering the enlarged hypoglossal canal, particularly when using threedimensional reconstruction techniques [10]. Oelerich [12] reported a detailed demonstration of the vascular anatomy of the PHA by the using MRA and CTA in 1997, and Carina reported that contrast enhanced MRA is accurate at detecting pathology not only in the carotid vessels, but also in the vertebrobasilar circulation as a diagnostic alternative to digital subtraction angiography [15]. The usual PHA is mostly found incidentally without significant clinical symptom, but can be related to several clinical manifestations, such as hypoglossal nerve palsy, neuralgia of the glossopharyngeal neuralgia or intracranial aneurysm formation and provide a pathway for cerebral embolism in patients with carotid stenosis. Furthermore, PHA is the mainly exclusive feeder of the posterior circulation because of hypoplasia or aplasia of ipsilateral or bilateral vertebral and posterior communicating arteries. This means that temporary clamping carotid artery, during carotid endarterectomy presents ischemic risks [2]. Still, there were no reported clinical symptoms associated with a variant persistent hypoglossal artery. But, we suppose that the clinical implications of the variant of PHA may be the same as usual PHA, because it also makes another arterial bifurcation that may induce aneurysm formation hemodynamically. And it passes through the hypoglossal canal that can irritate the hypoglossal and glossopharyngeal nerve,
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and has a same role as an exclusive feeder of posterior circulation too. Sometimes, ECA may be ligated for wounds, resection of the upper jaw, hemorrhage from the tonsils, cutting off blood supply for hypervascular tumor or intractable epistaxis. For example, in extirpation of the trigeminal ganglion, hemorrhage has been such an annoying and dangerous factor that a preliminary ligation or compression of the ECA is frequently resorted to. Then, rare but, that may increase the risk of ischemia in the patients with the variant of PHA. In conclusion, the PHA is a rare anastomosis between carotid and vertebrobasilar system. Furthermore, the variant of PHA arising from ECA is extremely rare, but supposed to have the significant clinical implications. Thus, the recognition of the existence of such a variant vessel like our case may not be ignored before planning neuroradiologic intervention or surgical procedures to prevent possible risks. Acknowledgments There were no grant supports. We kindly thank Kim Sung Eun for the artwork.
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