A rare metastatic myositis ossificans of obturator muscle secondary to urothelial carcinoma

The most frequent metastatic sites of the urothelial bladder cancers (UBCs) are bones, lungs, lymph nodes, liver, pleura, and brain. In the literature, skeletal muscle metastases from UBC have been rarely reported. We report a case of a 65-year-old male with metastatic myositis ossificans to obturator muscle 14 months after radical cystectomy performed for a muscle invasive transitional cell carcinoma. An abdomen computed tomography scan showed a lesion of about 8 cm in diameter in the left obturator muscle with myositis ossificans aspect. Ultrasound guided biopsy specimen of the left obturator muscle revealed poorly differentiated metastatic urothelial carcinoma with malignant myositis ossificans aspects. The patient refused additional surgery and received systemic chemotherapy and radiotherapy at the site of the lesion. The patient more than 6 months after treatment has a good performance status with a partial reduction of the mass and negative imaging for metastases in the follow-up.