Sino-orbital osteochondroma with malignant transformation to osteosarcoma

Purpose: Osteosarcoma is an aggressive malignant osteogenic tumor that commonly arises in long bones of pediatric populations. Primary osteosarcomas of the head and neck are rare, comprising less than 0.5% of malignancies in this region, usually affecting the mandible or maxilla. Here we present an extraordinary case of a rare benign osteochondroma of the ethmoid sinus and bilateral orbits evolving to an intermediate grade osteosarcoma. Observations: An 80-year-old woman with a history of right orbital tumor resection 20 years ago presented to our clinic with right eye proptosis and palpable bony prominence of the right orbit and nasal bridge. Partial resection demonstrated sino-orbital osteochondroma. Relapse a year later prompted repeat partial resection with unchanged histology. The patient was followed clinically until an abrupt relapse four years after initial presentation. Imaging demonstrated a large bony mass involving the right orbit, ethmoid and frontal sinuses, and anterior cranial fossa. Repeat debulking confirmed transformation to intermediate grade osteosarcoma. Conclusions: Osteochondroma is an extremely rare tumor in the orbit with only three cases previously reported. This patient is the first known case of benign osteochondroma of the orbit undergoing malignant transformation to osteosarcoma. Rapid progression of orbital osteochondroma should raise the suspicion of malignant transformation to osteosarcoma and prompt biopsy. Our patient subsequently underwent palliative radiation treatment and is stable with no gross progression.