Sternoclavicular joint pseudotumor: a clinicopathologic and radiologic study of 25 cases occurring in patients without prior neck dissection.

Pseudotumors of the sternoclavicular joint are rare, poorly characterized pseudoneoplastic lesions previously reported in association with prior neck dissection and thought to result from mechanical instability of the muscles of the shoulder girdle. We report 25 examples of this distinctive process, occurring in patients without a history of neck dissection, typically sent in consultation out of concern for a primary bone or soft-tissue tumor. Cases occurred in 14 women and 11 men (median = 68 years of age) and involved the sternoclavicular joint (17 cases), sternomanubrial joint (2 cases) or other nearby locations (6 cases). The masses ranged from 0.4 to 6.4 cm in size (median = 2.2 cm). Twenty-one patients (84%) had a clinical history of osteoarthritis involving other joints. Clinical follow-up (16 patients; mean = 11.4 months; range = 2-40 months) was uniformly benign, without evidence of recurrent disease. Radiologic review showed changes of osteoarthritis, often with cystic change. Pathologic features included degenerating cartilage, fibrinoid debris, pseudocyst formation, and florid proliferation of myofibroblasts and capillaries. The differential diagnosis of sternoclavicular/sternomanubrial pseudotumors centers around cartilaginous tumors of bone, in particular chondrosarcoma. Careful clinical, radiographic, and pathologic correlations are essential in arriving at the correct diagnosis and avoiding overtreatment.