he patient is a 25-year-old male who has a history of an ankle sprain some months ago. He has had persistent swelling in the ankle. He is working as a painter. There is pain in the ankle in the mornings and after workouts.

The patient is generally healthy and takes no prescription medicines or supplements. He has no allergies to medicines. He gives no history of previous surgery or illnesses. The rest of the review of systems is negative in detail. There is no significant family history.

Examination of the foot shows there is a soft, slightly mobile, soft tissue mass in the anteromedial portion of the right ankle that measures approximately five by 3 cm and appears to be about 1 cm thick. It is nontender. There is synovitis and swelling in the ankle generally. There is pain and tenderness along the course of the posterior tendon behind the medial malleolus. The range of motion of the ankle is slightly reduced. The overall alignment and arch of the foot is preserved. The neurovascular status is normal. There is no skin lesion and no cafe au lait spots are seen. No popliteal or inguinal lymphadenopathy is palpated.

An MRI and plain radiographs are examined. The plain radiographs do not show any fracture, and the ankle appears normal. On the MRI there is a soft tissue mass in the anterior ankle which is roughly as described above. It has heterogeneous appearance and it appears to be intra-articular. There is a relatively large fluid collection that seems to be centered on the FHL tendon posterior to the medial malleolus. It extends above and below the medial malleolus along the course of the tendon. The tendon has some abnormal signal intensity within its substance on some sequences, but this may be partial volume averaging. Other sequences appear to show an intact tendon surrounded by a large fluid collection.

Diagnostic possibilities include synovitis of the ankle, such as may be associated with Reiter's syndrome, or this also may be pigmented villonodular synovitis, which is my top choice. The possibility of an intra-articular sarcoma such as synovial sarcoma cannot be completely excluded. Biopsy and removal of the mass are planned as well as examination and possible debridement of the tendon.

What is your diagnosis?

Metastatic Tumors Case of the Month Bone Tumor Basics Tumor Jeopardy Fracture Risk Adamantinoma Aneurysmal bone cyst Angiosarcoma - High gd. Bizarre parosteal ost. pro. Brown tumor Chondroblastoma Chondromyxoid fibroma Chondrosarcoma Chordoma Desmoplastic fibroma Enchondroma Eosinophilic granuloma Epithelioid hemangioma Epithelioid hemangioend. Ewing's sarcoma Fibrosarcoma Fibrous dysplasia Florid reactive periostitis Giant cell tumor Glomus tumor Granulocytic sarcoma Hardcastle's syndrome Hemangioma Hemangiopericytoma Juxtacortical chondroma Langerhan's histiocytosis Malignant fibrous histio. Melorheostosis Metastatic cancer menu Multiple myeloma Myositis ossificans Neurofibroma of bone Nora's lesion Osteoblastoma Osteochondroma Osteofibrous dysplasia Osteoid osteoma Osteoma Osteomyelitis Osteopathia striata Osteopoikilosis Osteosarcoma Intro Paget's sarcoma Parosteal osteosarcoma Periosteal osteosarcoma Pigmented villonodular... Schwannoma of bone Solitary bone cyst Synovial chondromatosis Unicameral bone cyst

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