Myositis ossificans circumscripta in the psoas muscle with femoral neuropathy

Myositis ossificans circumscripta is a benign, self-limiting, ossifying soft-tissue mass that typically occurs in skeletal muscle of the extremities after trauma. Occurrence in the psoas muscle is rare with no reports of this condition presenting as femoral neuropathy. A 54-year-old woman visited our hospital because of progressive left leg pain and weakness, which she had experienced for 2 years. Physical examination indicated left femoral neuropathy, and a 6 cm × 5 cm mass was palpable in the left groin. Plain radiographs showed an irregular calcification over the left hip. Computed tomography of the pelvis showed a fusiform mass within the left psoas muscle. A modified ilioinguinal approach was used to excise the mass, and histologic examination confirmed the diagnosis. After surgery, the patient's symptoms resolved and there was no recurrence at 4 years' follow-up. Excision may be considered when a patient has a large, painful mass with neuropathy and significant functional impairment after conservative treatment.