Bursal Osteochondromatosis Overlying an Osteochondroma of a Rib. A Case Report*

Synovial chondromatosis is a rare, benign, pathological condition characterized by the production and intra-articular extrusion of cartilaginous nodules by metaplastic synovial tissue. These bodies often undergo endochondral ossification—hence the term synovial osteochondromatosis. The disease is idiopathic and appears as a monoarticular arthropathy of a diarthrodial joint, particularly the knee8.

Extra-articular lesions have been reported, but they are even rarer than their intra-articular counterparts. In these instances, the chondrometaplasia occurs in tenosynovial or bursal tissue and almost exclusively in the hands and feet9,11,14,16,20,22,26,27.

This report describes a case of bursal osteochondromatosis arising within an adventitious bursa over an osteochondroma of a rib. This phenomenon can mimic a malignant tumor and cause clinical confusion.

Case Report

A twenty-eight-year-old, right-hand-dominant male construction worker had a mass on the posterior portion of the right shoulder. The mass was painless and had gradually increased in size over a two-year period. The medical history was unremarkable with the exception of a remote right clavicular fracture.

Physical examination revealed a non-tender fourteen-centimeter-diameter mass in the scapulothoracic region that extended cephalad into the caudad posterior cervical region (Fig. 1). There was no atrophy or neurovascular compromise of the right upper extremity. The range of motion of the glenohumeral joint was normal. Scapular retraction was 25 per cent of normal, and upward scapular rotation lacked the terminal 30 degrees.

Fig. 1 Posterior photograph of the right scapulothoracic mass, which was firm, fixed, and non-tender to palpation.

Plain radiographs showed diffuse mottled mineral deposition within the lesion (Fig. 2). Computed tomography showed an area of dense calcification at the core of the mass that abutted a cephalad rib and was surrounded by numerous uniformly distributed discrete opacities (Fig. 3). The lesion was not directly …

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