[Benign giant cell tumor of the tendon sheath. A differential diagnosis of cutaneous tumors near the joint].

Giant cell tumour of the tendon sheath, though rather a common connective tissue tumour, is rarely mentioned in the dermatological literature. It is a benign, slow-growing tumour arising from the synovia and it is most frequently located on the joints of the fingers. It becomes manifest clinically as a firm, skin-coloured nodule fixed to the underlying tissue. The histological picture is characteristic and shows osteoclast-like giant cells, histiocytic cells, foam cells and focal haemosiderosis. It probably reflects a reactive process similar to that of fibrous histiocytoma. The therapy of choice is excision, with a small margin of uninvolved tissue to avoid recurrences.