Unusual shoulder synovitis secondary to an osteoid osteoma without a nidus in the coracoid process: delayed appearance of a nidus

Abstract

Shoulder synovitis is a nonspecifi c manifestation of various diseases such as rheumatoid arthritis, stiff shoulder, infection, and rarely osteoid osteoma. Among them, osteoid osteoma is a benign tumor that occurs in bone. It is not a rare disorder, accounting for about 5% of all bone tumors and 11% of benign bone tumors. More than half of osteoid osteomas occur in the femur and the tibia, the long bone of lower extremities. Although the tumor may develop in any location, including the humerus, talus, and vertebrae, its incidence in the scapula is reportedly less than 1%. The tumor observed in the coracoid process, in particular, is extremely rare in the English-language literature. As osteoid osteoma develops around a joint, it can manifest in a variety of symptoms apart from the classic night pain, making the diagnosis diffi cult. If a nidus is not confi rmed at radiographic examinations, surgeons are likely to make a wrong diagnosis. In this article, we report a rare case of osteoid osteoma of the base of the coracoid process that mimicked shoulder synovitis associated with chronic osteomyelitis. Moreover, it did not have a nidus initially. This study was approved by the scientifi c review board at our hospital and was conducted in accordance with the World Medical Association Declaration of Helsinki of 1964, as revised in 1983. The patient was informed that data concerning the case would be submitted for publication, and he consented.