[Fibrous dysplasia of the petrous bone]

Fibrous dysplasia named after Jaffè and Lichtenstein is a benign, self-limiting disorder of the bone structure. The normal bone is replaced by cellular fibrous connective tissue. Fibrous dysplasia can be differentiated into monostotic and polyostotic forms and the McCune-Albright syndrome (combination of polyostotic areas in the bone with hyperpigmentation of the skin and endocrinological disturbances). The rare disease is predominantly found in the 1st to 3rd decade of life in the femur or humerus. In about 15% of all cases it affects the facial bones, and one-third of these is located in the jaw bone. Extremely rare is the invasion of the petrous bone. A 45-year-old female patient was examined because of tinnitus persisting for 1 year. In addition, she was suffering from increased hearing reduction and recurrent vertigo. The CT and MRT showed a milky glass-like tumor, which was limited by an osteolytic process situated in the left petrous bone. The process was removed via the mastoid. Histological examination revealed fibrous dysplasia. A highly differentiated osteosarcoma and an ossifying fibroma as important differential diagnoses have to be excluded because of the different therapeutic consequences.