Neuroradiology Case of the Week

Case 39

Francisco Garcia-Morales, MD and P-L Westesson, MD, PhD, DDS

Clinical Presentation: A 53-year-old male presented with a two-year history of pain and cramping in his tongue.

Radiological Findings: Axial and coronal images (Figs. 1A&B) demonstrate normal architecture and signal intensity of the tongue. Images of the skull base, however, demonstrated an enhancing lesion in the region of the hypoglossal canal on the right side (arrows in Figs. 2A-C). On another slice the widening of the hypoglossal canal can be appreciated (arrows in Fig. 3).

Figure 1: Axial T2-weighted image (A) and coronal T2-weighted with fat suppression (B) show normal morphology of intrinsic tongue muscles (arrows).
Figure 2: Axial T1-weighted images before (A) and after the administration of contrast (B) show the uniform enhancement of the right XII nerve schwannoma (arrows). T2-weighted image also shows the lesion with increased signal intensity (C).
	Figure 3: Axial T2- weighted image demonstrating the schwannoma in the direction of the hypoglossal canal.
Figure 4: Axial fat-suppressed after contrast administration demonstrating a large left hypoglossal nerve schwannoma with cisternal and hypoglossal canal involvement [3].

Diagnosis: Schwannoma of the 12th cranial nerve.

Discussion:
   Schwannoma is the second most common intracranial extra-axial neoplasm after meningiomas [1]. Most of the schwannoma arise from the 8th cranial nerve so-called acoustic neuromas or vestibular schwannoma. Schwannoma can affect other cranial nerves and have been most commonly seen in cranial nerves 7, 9, 10, 11 and 12. Hypoglossal schwannomas are uncommon and in a recent review found only one case in about 100 cases of XII nerve paralysis [3]. It is unknown why so many schwannoma arise from the 8th cranial nerve and so few from the other cranial nerves. The most characteristic clinical finding of patients with 12th nerve schwannoma has been unilateral lingual atrophy with fibrillation and tongue deviation [2].
   MRI is clearly the best diagnostic tool for this entity especially because of schwannomas' tendency to enhance after Gadolinium administration, improving the contrast resolution and better depicting them from the surrounding brain and bone tissue with great distinction, as can be easily appreciated in this case.
   Another example of a hypoglossal schwannoma from the literature is shown in Figure 4 [3].

References:

1. Osborn AG, Blaser SI, Salzman KL, Brain, 2002, WB Saunders, p 168-170.
2. Okura A, Shigemori M, Abe T, Yamashita M, Kojima K, Noguchi S: Hemiatrophy of the tongue due to hypoglossal schwannoma shown by MRI. Neuroradiology 1994; 36:239-240.
3. Beldarrain MG, Canton GF, Garcia-Monco JC. Hypoglossal Schwannoma: an uncommon case of 12th nerve paralysis. Neurología 2000; 15:182-183.