Hyperostosis in orbital rhabdomyosarcoma.

Rhabdomyosarcoma is the most common soft-tissue sarcoma in paediatric patients and may arise as a primary orbital neoplasm. Imaging studies show a unilateral solitary orbital lesion. With larger tumours, erosion of the adjacent orbital walls is a common accompanying bony change. We present an unusual case of rhabdomyosarcoma in a preschool girl with proptosis and temporal bossing. Imaging studies showed a homogeneous, well-delineated, extraconal mass of the right orbit with hyperostosis of the adjacent sphenoid bone. After excision of the mass and debulking of the sphenoid bone, histopathology showed embryonal rhabdomyosarcoma with no malignant infiltration of the adjacent bone. This is the first reported case of hyperostosis associated with rhabdomyosarcoma. Periosteal reaction is the proposed underlying mechanism.