A 5 year old Arabian mare was evaluated for a non‐painful swelling located dorsal to the right carpus which had been present for 2 years. Radiographically, multiple mineralized bodies were identified dorsal to the distal radius and carpus in the region of the tendon sheath of the extensor carpi radialis muscle. The radiographic appearance of the carpal bones was within normal limits. On ultrasound examination, multiple hyperechoic foci with posterior shadowing were seen adjacent to the extensor carpi radialis tendon. There was minimal distension of the tendon sheath and no abnormalities within the substance of the extensor carpi tendon were identified. Considering the radiographic and sonographic findings, a presumptive diagnosis of tenosynovial osteochondromatosis was made. Histological confirmation of this diagnosis was not obtained as the owner declined further diagnostic evaluatio
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