Myositis ossificans mimicking parosteal osteosarcoma: a case report and literature review.

Myossitis ossificans (MO) is an aberrant reparative process that causes benign heterotopic ossification in soft tissue. We report a case of MO presenting as a large mass located at the dorsal aspect of the distal thigh, with no history of trauma, with radiological and clinical features mimicking parosteal sarcoma. An incisional biopsy was performed and the mass was excised. The histological features identified the lesion as MO. In half of the cases, these ossifications may adhere to the periosteum. In these cases, the lesion is known as parosteal MO, which may be confused with a parosteal osteosarcoma. This parosteal MO seldom becomes malignant. We emphasize the importance of a differential diagnosis of MO, since these lesions may simulate tumours and lead to misdiagnosis.