Congenital lesions of the internal acoustic canal (lipoma).

The most common congenital lesions that occur in the cerebellopontine angle cistern and internal acoustic canal are epidermoidomas, arachnoidal cysts, dermoids, and lipomas. The lipoma, which is the least common, is the most characteristic on magnetic resonance imaging (MRI). The high intensity of this fatty lesion makes it very conspicuous on MRI without contrast (figure). Therefore, it is imperative to obtain both pre- and postcontrast images to differentiate a lipoma from an acoustic neuroma. On postcontrast imaging, an acoustic neuroma usually enhances vividly and is indistinguishable from a lipoma. [1] Moreover, the physician might also encounter an intracanalicular lipoma as an incidental finding, as happened in the case presented here.

From the Department of Radiology, MacNeal Hospital, Berwyn, Ill.

Reference

(1.) Valvassori GE, Mafee MF, Carter BL. Imaging of the Head and Neck. New York: Thieme Medical Publishing, 1995