Giant-cell tumor of the synovial membrane: localized nodular synovitis in the knee joint.

Giant-cell tumor of the synovia is a benign neoplasm characterized histologically by proliferating histiocytes bearing lipids and hemosiderin intermingled with a variable number of multinuclear giant cells. Areas of predilection are the hand, and in the case of synovial joints, the knee joint is particularly affected. Clinically, patients have signs of mechanical derangement and, with the knee joint, meniscal symptoms and locking are often present. Joint effusion without previous trauma is another typical finding. Diagnosis is carried out by radiographic tools and has to be confirmed histologically. Giant-cell tumor of the synovia is treated by local excision either by arthroscopy or by arthrotomy. To our knowledge, the case we present is the largest giant-cell tumor of the synovia in the knee joint ever described in literature.