Clinical History
fibrous dysplasia of the temporal bone.
Imaging Findings
A 28 year-old male patient was admitted at our Hospital with a right temporal swelling and bulging.
Physical examination revealed a hard bony-like mass of the right temporal region and a trismus with a maximal inter-incisor distance of 2 cm. External auditory canals, tympanic membranes and audiogram were normal. The patient reported occasional otalgia but denied vertigo.
AP and lateral skull X-rays demonstrated an expanded temporal bony cortex, alternate areas of condensation (petrous apex, mastoid) and radiolucency (squamous portion of the temporal bone). Lateral view showed an oval radiolucent lesion of the vault with marginal sclerosis above the external auditory canal.
Non enhanced CT was performed to evaluate the bony involvement and assess the adjacent soft tissue.
CT showed extensive involvement of right temporal and sphenoidal bone by pagetoid fibrous dysplasia producing characteristic ground-glass appearance. Diploic space appeared widened. The outer table was either thinned or thickened. Some localized defects of the outer table were demonstrated. The inner table was thinned but no disruption could be found.
The external auditory canal was narrowed. The middle ear structures, the jugular foramen, facial nerve and temporo-mandibular joint were not affected and the right temporal muscle appeared swollen behind the TMJ.
Fibrous dysplasia was strongly suspected and confirmed by histopathological examination.
Discussion
Fibrous dysplasia (FD) is a slow growing disorder of the bone, characterized by abnormal proliferation of fibrous tissue with normal or immature bone. The disease may be monostotic (70 %) or polyostotic (30 %).
The aetiology of FD is controversial : a gene mutation during embryogenesis is likely.
The mean age of presentation of fibrous dysplasia (FD) is during the 1st and 2nd decades.
The disease may involve any bone in the body.
In monostotic variety, craniofacial skeleton is a common site (10-25 %) but temporal bone involvement is unusual (18-20 %)(1).
The most common clinical symptoms of FD of the temporal bone are hearing loss (80 %), temporal swelling (25 %), otorrhea, otalgia and rarely trismus (3).
The otologic examination may reveal narrowing of the external auditory canal (80 %), conductive and/or sensorineural hearing loss.
Diagnosis relies on radiographic features.
3 patterns were described : Pagetoïd (56 %) : a mixture of dense and radiolucent areas of fibrosis; Sclerotic (23 %) : homogeneously dense; and Cystic (21 %) spherical or ovoïd lucency surrounded by a sclerotic border (2). The more osseous tissue the higher the radiographic density. A mixture of fibrous and osseous tissue produces the classic « ground glass » appearance.
CT is very useful, assessing the extent of FD within the temporal Bone. On CT, the petrous bone, the otic capsule, the inner ear, the external auditory canal, the jugular foramen and the TMJ involvement (2) should be studied.
CT is also helpful in monitoring the progress of the disease and to detect early complications such as cholesteatoma (40 %), malignant degeneration (very rare, 0,4 %), recurrence (3).
CT findings can be used for surgical planning to minimize surgery, to reveal any growth, to detect the development of secondary disorders and finally to prepare esthetic bone reconstruction if necessary.
Follow-up is mainly based on CT. There is no established rule : however if surgery was complete, a first examination can be performed 6 months later. If the result is deemed satisfactory, no subsequent CT is scheduled except in case of clinical recurrence.
If surgery was incomplete, CT can be less delayed and more frequently performed depending on clinical and surgical data.
CT findings are pathognomonic of the disease : homogeneous condensation and an expansion of cortex is characteristic.
Differential Diagnosis List
fibrous dysplasia of the temporal bone.
Final Diagnosis
fibrous dysplasia of the temporal bone.
