Fibrous dysplasia is an uncommon disorder of unknown etiology. It represents a bone developmental disorder, specially a defect in osteoblastic differentiation and maturation. FD could be monostotic (70% of cases) or polyostotic [1]

Approximately 3% of the patients with FD have the so-called McCune-Albright syndrome, in which bone involvement is followed by skin lesions and endocrine pathologies.  Virtually any bone in the body can be affected. It is a nonhereditary disorder of unknown cause [2]

Of interest to Otorhinolaryngology is the fact that fibrous dysplasia may involve craniofacial bones, causing deformities and dysfunctions, such as hearing loss, retroauricular bulging, and complications (cholesteatoma and facial nerve damage (Papadakis CE et al, Ear Nose Throat J 2000; 79(1):52-7).

The disease can involve any bone in the body. In the head and neck, the skull and facial bones are involved in 10-25% of cases of monostotic fibrous dysplasia and in 50% of the polyostotic variety. Involvement of the temporal bone is relatively rare.[3]

Within the temporal bone, involvement of the auditory canal is the most common manifestation of fibrous dysplasia, seen in approximately 8% of patients leading to a conductive hearing loss.  Middle ear involvement is uncommon and results from secondary cholesteatoma from long standing external canal stenosis. Fibrous dysplasia may involve the otic capsule, cochlea and labyrinth. Involvement of the inner ear may also encroach on the intratemporal facial nerve and facial nerve palsy may rarely be seen (Megerian CA et al 2005), and is reportedly seen in 10% of FD of temporal bone.[1]

Malignant transformation has not been reported for temporal bone fibrous dysplasia, but it has already been reported in other disease sites, with 2/3 of these transforming into osteosarcoma.

CT Scan may show the abnormality and Serum chemistry may show deranged Serum calcium, phosphorous and alkaline phosphatase, but these are not pathognomic, and it is often difficult to make a diagnosis of FD of temporal bone on isolated radiological or clinical data. Histology of excision biopsy of bone specimen may be needed.

Important differential diagnoses of temporal bone fibrous dysplasia include Paget’s disease, hyperparathyroidism, local reaction to meningioma, osteoma, eosinophilic granuloma, steochondroma, and sarcomatous neoplasm.

Not all cases of FD of temporal bone requires treatment, largely because there are no effective conservative treatment to control FD. Watchful waiting and follow up is all that is needed in FD with little or no symptoms

Surgery is indicated in FD of Temporal bone with significant symptomatology, especially associated with bone invasion of external auditory canal (enough to produce conductive hearing loss), recurrent infections and secondary cholesteatoma in the external auditory canal. The 3 main goals of surgery include restoration of the function, prevention of complications, and esthetical improvement. Radiotherapy is highly discouraged because of the risk of malignant transformation.

Further Readings

1. Vanier S. Júnior1, Eduardo C. Andrade1, Ana L. S. Didoni1, José C. Jorge2, Nelson S. Filho3, Fabiana R. Yoshimoto3.Fibrous dysplasia of the temporal bone: case report and review of the literature. Rev Bras Otorrinolaringol.V.70, n.6, 828-31, nov./dec. 2004
2. Magu S, Mishra DS, Sood AK, Sharma N. Fibrous dysplasia of the temporal bone. Neurol India [serial online] 2002 [cited 2009 Dec 24];50:374. Available from: http://www.neurologyindia.com/…..3/374/1417
3. Fibrous Dysplasia – eMedicine – http://emedicine.medscape.com/…..4-overview

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