A cystic protrusion of the wrist is one of the symptoms of a tendon sheath cyst. Tenosynovial cyst (thecal cyst) is the most common type of mass on the dorsal side of the wrist and can also occur on joint capsules and tendon sheaths in other parts of the body. Diagnosis: 1. A hemispherical, smooth-surfaced, tense, cystic mass on the dorsal side of the wrist, palmar side, or dorsum of the foot. 2. The mass grows slowly, with soreness or pain on pressure and a fixed base. 3.X-ray film shows no change of bone and joint. Differential diagnosis between tendon sheath cyst and other bone diseases: tendon sheath cyst should be distinguished from giant cell tumor of tendon sheath, epidermoid cyst, lipoma, fibroma, rheumatoid arthritis and so on. When the cyst is more tense, the texture is harder but still elastic and cystic, and the mass is not mobile because it has a fixed tip. There is usually no pressure pain or light pressure pain. Seed cysts located on the metacarpal side of the proximal phalanges of the fingers are often mistaken for osteophytes because of the small, hard masses. Tenosynovial cysts that occur within the tendon can move with the movement of the tendon and when one end is pressed, the mass can move or expand toward the other end.