American Journal of Neuroradiology 20:157-158 (1 1999)
© 1999 American Society of Neuroradiology
ARTICLE
Dilated Venous Plexus of the Hypoglossal Canal Mimicking Disease
Stephen L. Stuckey
,a
a From the MRI Unit, The Alfred Hospital, Commercial Rd, Prahran 3181, Australia.
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Abstract
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Summary: This article describes a case of prominent emissary
veins of the hypoglossal canal protruding into the cerebellomedullary
cistern mimicking disease, such as a nerve sheath tumor. The
diagnosis and differentiation in this instance were confirmed
by MR angiography and a review of alternative imaging planes.
A diagnosis of hypoglossal canal lesions should be made with
caution, as these lesions are quite rare, and vascular anomalies,
such as those described, may mimic disease in this region.
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Introduction
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The hypoglossal (or anterior condyloid) canal is infrequently
the site of disease. It contains the rootlets of the hypoglossal
nerve, emissary veins, and occasionally a branch of the ascending
pharyngeal artery (
1). The venous plexus of the hypoglossal
canal, which may occasionally be a single vein, joins the sigmoidal
sinus to the internal jugular vein with contributions from the
basilar venous plexus and, also, according to our images, the
upper cervical spine epidural plexus (
2). Normal MR imaging
appearances have been well described, and include enhancement,
postulated to represent venous structures, and occasionally
linear nonenhancing structures, thought to represent portions
of the hypoglossal nerve (
1). This article describes a case
of marked asymmetrical protrusion of a vascular structure into
the cerebellomedullary cistern immediately adjacent to the hypoglossal
canal, illustrating a pitfall in the diagnosis of disease in
this region.
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Case Report
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A 54-year-old man with a history of possible temporal lobe epilepsy
underwent MR imaging, which showed a masslike region related
to the intracranial aspect of the right hypoglossal canal, measuring
approximately 1 cm in diameter isointense with cerebral cortex
on T2-weighted images (
Fig 1A). The patient was asked to return
for a dedicated posterior fossa contrast-enhanced study, which
showed the lesion protruding from the right hypoglossal canal
into the right cerebellomedullary cistern (
Fig 1B). A smaller,
similar finding was noted in relation to the left hypoglossal
canal (
Fig 1C). The findings were thought to be a normal variant
related to the emissary venous structures of the hypoglossal
canal. Contrast-enhanced coronal images also suggested these
regions were contiguous with vascular structures, extending
toward or away from the cervical epidural venous plexus (
Fig 1D).
One week later, the patient was examined with a modified
MR angiographic technique to confirm the above diagnosis. A
2D time-of-flight MR angiogram without saturation bands obtained
in the region of the skull base (
Fig 1E) showed increased signal
intensity within the region of interest, suggestive of flow
within the lesion. Three-dimensional phase-contrast MR angiography
was also performed with velocity encoding of 15 cm/s; however,
this study did not show flow within either of the regions immediately
medial to the hypoglossal canals, presumably reflecting extremely
slow venous flow.
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FIG 1. MR imaging findings in a 54-year-old man with a history of possible temporal lobe epilepsy.
A, Fast T2-weighted axial (parallel to the plane of the hippocampal formations) spin-echo image (4700/112/2) shows a 1-cm isointense mass in the right cerebellomedullary cistern (arrow).
B, Noncontrast T1-weighted axial spin-echo image (640/11/2) shows a round masslike structure (long arrow) extending from the right hypoglossal canal approximately 1 cm in diameter with a similar, less-impressive left-sided finding (short arrow).
C, Contrast-enhanced T1-weighted axial spin-echo image (760/11/3) shows marked enhancement of both regions.
D, Contrast-enhanced T1-weighted coronal spin-echo image (760/11/3) shows continuity of enhancement from the cervical epidural venous plexus to the hypoglossal canals, including the masses protruding into the cerebellomedullary cisterns.
E, Two-dimensional time-of-flight MR angiographic partition image shows patchy hyperintensity (arrow) within the larger right cerebellomedullary cistern, which in the absence of high signal on a T1-weighted image indicates blood flow (46/8.7/2; flip angle, 45°).
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Discussion
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The benefits of increased contrast resolution and multiplanar
imaging capabilities of MR imaging in improving diagnostic capability
have also led to numerous potential pitfalls in diagnosis (ie,
normal appearances or normal variants mistakenly interpreted
as disease). To consider contrast enhancement alone as proof
of disease is fraught with danger, particularly in the region
of the skull base, where there are many vascular structures.
The case presented here clearly illustrates the need for caution
despite the appearance of an enhancing mass protruding from
a skull base foramen.
The normal MR imaging appearance of the hypoglossal canal has been well described (1). Included in this description was extension of enhancement extracranially beyond the bony canal. This case shows that the associated venous enhancement may protrude into the cerebellomedullary cistern, mimicking disease. One should, however, confirm that such findings do not relate to the patient's symptoms, as at least one case report has suggested that dilated venous structures within the hypoglossal canal may be symptomatic (3). The principal differential diagnostic possibilities include the presence of a nearby arteriovenous fistula with enlarged draining veins and a prominent venous plexus related to impaired jugular venous return. These possibilities may provide other imaging findings to suggest their presence, such as more widespread venous dilatation or direct evidence of a pathogenesis, such as internal jugular vein thrombosis. The nature of such a lesion is easily clarified by the addition of alternative imaging planes alone or in combination with flow-sensitive sequences.
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Footnotes
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101 Address reprint requests to Dr. Stephen L Stuckey.
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References
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Voyvodic F, Whyte A, Slavotinek J. The hypoglossal canal: normal MR enhancement pattern. AJNR Am J Neuroradiol 1995;16:1707-1710[Abstract]
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Williams PL, Wariwick R. Gray's Anatomy 36th ed. Edinburgh: Churchill Livingstone; 1980; 308,750
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Shiozawa Z, Koike G, Seguchi K, et al. Unilateral tongue atrophy due to an enlarged emissary vein in the hypoglossal canal. Surg Neurol 1996;45:477-479[Medline]
Received February 9, 1998;
accepted after revision May 12, 2000.
TOP
Abstract
Introduction