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Findings: T1 weighted axial pre and post contrast images as well as T1 weighted post contrast coronal images demonstrate a left cerebellopontine angle mass. This demonstrates low signal on the T1 weighted images and enhances peripherally and heterogeneously centrally following the intravenous administration of contrast. In addition, there is widening of the internal auditory canal.
Diagnosis: Acoustic schwannoma.
Discussion: Acoustic schwannomas account for approximately 75% of all cerebellopontine angle masses. They most commonly arise from the vestibular branch of the 8th nerve. However, they can arise from other cranial nerves such as the facial or trigeminal nerve. Involvement of the intracanalicular portion of the 8th nerve produces enlargement and erosion of the internal auditory canal.
The lesions are commonly hypo to isointense with brain on T1 weighted images. There is marked enhancement following the intravenous administration of contrast. On T2 weighted images, lesions are typically iso to slightly hyperintense.
The differential diagnosis for cerebellopontine angle masses include acoustic schwannomas, meningiomas, epidermoids, arachnoid cysts and aneurysms. Specifically, the superior cerebellar as well as the anterior inferior cerebellar artery course through the cerebellopontine angle.
The presentation of bilateral schwannomas involving the 8th cranial nerve can be seen with neurofibromatosis 2. Other lesions such as multiple meningiomas and epidermoid tumors can be seen in these patients as well.
References:
James P. Earls, MC, et al. Radiographics. General Case of the Day.
November 1994;1424-1427.
Osborn AG. Diagnostic Neuroradiology. Mosby, St. Louis, 1994;437-448.
Taveras JM. Neuroradiology, 3rd Edition, Williams & Wilkins, 1996:684-693.
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