Giant-cell tumour of tendon sheath
It is also called giant-cell synovioma or localized nodular tenosynovitis. It is a firm, dermal or subcutaneous nodule, composed of scattered multinucleated giant cells set on a background of proliferating spindle cells in a collagenous matrix. It usually occurs on the fingers. The cause is unknown and usually presents in mid-life as a single, firm, rubbery, subcutaneous mass on the finger. The nodule is usually asymptomatic, but in occasional cases there may be pain, numbness or stiffness of the digit. There is a strong association with osteoarthritis. The lesions do not regress, and they can persist for more than 20 years.