Epidermoids involving the temporal bone: clinical, radiological and pathological aspects.

Epidermoids or congenital cholesteatomas arise from aberrant epithelial remnants and are, therefore, considerd blastomatous malformations. Their predilective sites are the intracranial cavity, the diploe of the skull and the spinal canal. In the base of the skull the temporal bone is the most frequent site. Epidermoids account for about 0.2-1.5 percent of all intracranial tumors. The majority originate in the cerebello-pontine angle where they account for 6-7 percent of all tumors. Their age incidence reveals a great scatter from birth to 80 years. The majority are recognized during the third and fourth decades with the onset of clinical symptoms occurring much earlier. They affect males more frequently than females. Their delicate capsule with a whitish mother-of-pearl sheen lends them a typical appearance. Epidermoids are generally slow growing lesions which may remain asymptomatic for years. The irritative effect of their content, however, can produce symptoms of dysfunction and intense inflammation. Malignant changes occur infrequently. Diploic epidermoids are easily recognized, whereas, intradural epidermoids are more difficult to identify. Epidermoids may arise in the vicinity, on the outer aspect or within the temporal bone. Epidermoids originating in any of these locations have certain characteristic features which may arouse suspicion of their presence. Examples of an epidermoid with origin in the typical locations within the temporal bone and cerebello-pontine angle are discussed to portray their individual characteristics.