Malignant degeneration of an epidermoid of the temporal bone.

An epidermoid (congenital cholesteatoma) in the CPA is similar to an acoustic neuroma but can often be differentiated by a normal internal auditory canal and increased radiolucent areas on CT scan. The presence of an atypical lesion on the CPA is suggestive of a metastatic lesion and warrants careful evaluation for an occult primary lesion prior to resection. Despite increasingly sophisticated techniques for removal of these lesions, the possibility of complete resection is slim and the ultimate prognosis is poor.