Synovial cyst of the fifth digit in a cat.

A synovial cyst of the fifth digit of the left forelimb in a 15-year-old cat was diagnosed. Radiographs showed severe osteoarthritis of the interphalangeal and metacarpophalangeal joints with soft tissue swelling. An ultrasound examination of the digit revealed a cystic structure. Following amputation of the digit, the cyst recurred 3 months later palmar to the carpus and metacarpus. The aetiology of synovial cysts is discussed.