Craniofacial involvement in fibrous dysplasia may be considered a “monostotic” location despite involvement of several craniofacial bones or more rarely be part of a polyostotic fibrous dysplasia. Although more cases are monostotic, a higher proportion of polyostotic cases have craniofacial involvement (50%) versus craniofacial involvement in monostotic cases (25%) – although recall monostotic disease is overall more common.
Within craniofacial fibrous dysplasia involvement of the anterior bones is more common than lateral or posterior bones with a recent study in the more sensitive CT era suggesting that ethmoidal involvement is the most common. Presentation may be asymptomatic/incidental, due to evolution of a lump or due to pressure effects.
With regards to the temporal bone involvement of the external auditory canal as in this case may result in canal narrowing and conductive hearing loss. Involvement of the middle and ossicles does not usually occur although occasional cases of destruction of these structures have been described. This is usually the result of obstructive cholesteatomas that have been described following external canal occlusion. Inner ear involvement is also rare as is involvement of the facial nerve. Extension to the temporomandibular joint can cause joint deformity and present with trismus.
Fibrous dysplasia has been described on plain films as pagetoid (ground glass opacity with small lucencies), sclerotic or cystic. However, these distinctions are not as clear at CT. Margins of involvement are variably described as well-defined or ill-defined, suggesting both can occur. In contradistinction to one of the main differential diagnoses, Paget’s disease, trabecular thickening or disruption of the cortex do not occur. Secondary aneurysmal bone cyst formation is a recognised complication.
Diagnosis is based on typical appearances, predominantly at CT which also assists in differentiating fibrous dysplasia from other osteodystrophies of the skull base, including otosclerosis, osteogenesis imperfecta, Paget’s disease, and osteopetrosis. MRI may be of assistance (usually T1 intermediate, T2 helpful if low signal - a common manifestation- but can be heterogeneous including high signal too, heterogeneous contrast enhancement post Gadolinium).
Treatment of this benign condition is usually conservative with partial surgical resection considered to relive pressure effects. Radiation is a historical treatment that is ineffective and was associated with sarcomatous degeneration.