Fibrous Dysplasia of Temporal Bone Presented as a Solitary Osteochondroma: A Case Report

INTRODUCTION: Fibrous dysplasia is a benign disorder of unknown etiology. It represents a disturbance of normal bone development – a defect in osteoblastic differentiation and maturation that originates in the mesenchymal precursor of the bone. It is characterized by slow progressive replacement of bone by abnormal isomorphic fibrous tissue. Temporal bone involvement is extremely rare. We report an unusual case of fibrous dysplasia presented like a solitary osteochondroma. CASE REPORT: A 14-year-old girl presented with the complaints of slow-growing swelling on the left temporal region in scalp near left eye for 2 years. The swelling was small to begin with, which increased gradually over a period of 2 years. There were no other presenting symptoms. Hearing was normal. Parents of the patient were concerned with cosmesis only. She had undergone 3D CT scan of skull where it showed bony outgrowth with features suggestive of exostosis. This bony outgrowth had cortex in continuity to cortex of temporal bone and medullary canal same as that of the temporal bone and ground-glass appearance. Repeat CT scan showed bony outgrowth with cortical continuity and had pedicle. It was suggestive of pedunculated osteochondroma. There was no evidence of malignant transformation as swelling showed calcified osteoid-like mass throughout. Hence, the clinical and radiological diagnosis of the left temporal bone solitary osteochondroma was made. However, histopathology showed irregularly shaped bony trabeculae in fibrous stroma of variable cellularity without accompanying osteoblast rimming. Thus, diagnosis was fibrous dysplasia of bone. Histopathological slide was reviewed by two independent pathologists with same conclusion. CONCLUSION: Our case was unique in that the lesion presented clinically and radiologically as solitary osteochondroma. However, in hindsight, lack of cartilage cap on CT scan should have prompted us to look for another diagnosis. To the best of our knowledge, this was unique varied presentation of fibrous dysplasia of temporal bone.