Osteoid osteoma of the proximal humerus: two misleading cases.

Osteoid osteoma (OO) is a common bone disease, making up 2.6% of all bone tumors and 11% of all benign bone tumors. The typical clinical features include variable pain, often worse at night and markedly responsive to salicylates, and a characteristic roentgenographic appearance of bony sclerosis around a lucent nidus. Although this might suggest an easy diagnosis, diagnosis can often be delayed 1 or 2 years, especially when the lesion is located near a joint. Such a lesion at the upper end of the humerus is rare. In a series of 245 cases Dahlin found only 5 cases out of 18 involving the humerus. Rockwood, in a series grouping OO and osteoblastoma together, identified a 10% to 15% frequency out of all shoulder tumors. The misleading aspects of juxtaarticular OO are well known. However, involvement of the superior humeral epiphysis has only been reported briefly in one patient. The two cases presented in this article show the diagnostic difficulty encountered in this location and misleading clinical, radiologic, and sometimes histologic aspects of patient evaluation.