Dermoid of the petrous apex.

Radiolucent lesions of the petrous apex of the temporal bone are unusual, with an incidence of less than 1%. The differential diagnosis includes giant apical air cells, acquired cholesteatomas, congenital cholesteatomas or epidermoids, true dermoids and teratomas, and benign and malignant neoplasms. The authors present an extremely rare case of a true dermoid of the petrous apex which eroded into the clivus of the occipital bone, and discuss the differential diagnosis, symptomatology, and diagnostic work-up. Complete resection is the preferred management if it can be done easily and and safety; however, since the lesions are usually unresectable and manifest few symptoms, a conservative surgical approach for diagnosis and decompression is urged. The authors discuss in detail a surgical approach which allows for preservation of function and hearing, as well as diagnosis and immediate decompression. Further surgical decompressions, when needed, can be easily, quickly, and safely achieved through the same surgical approach. A review of the medical literature has revealed no previously reported case of a true dermoid involving the petrous apex.