Petrous bone epidermoid cyst caused by penetrating injury to the external ear: Case report and review of literature.

Epidermoid cysts are histologically benign, slow-growing congenital neoplasms of the central nervous system that may arise from retained ectodermal implants. The epidermoid lesions are generally caused during the 3(rd) to 5(th) week of gestation by an incomplete cleavage of the neural tissue from the cutaneous ectoderm, though it can also happen later in life due to introduction of skin elements by skin puncture, trauma or surgery. We present this unique case of a petromastoid epidermoid cyst associated with ipsilateral cerebellar abscesses, presenting 20 years after a penetrating trauma to the external auditory canal. Radical excision of both lesions and revision of the previous fistulous tract was performed. We present the diagnostic challenge and the operative treatment of this unique case, which to our knowledge is the first where an epidermoid cyst and an adjacent brain abscess occurred as a result of a single traumatic event.