Synovial chondromatosis of the acromioclavicular joint.

A 53-year-old woman presented with swelling of 3 years' duration on the right anterior chest wall. A radiograph showed coarse calcifications around the subclavicular region and erosion of the ipsilateral acromioclavicular joint. Computed tomography also showed calcifications in soft tissue. Magnetic resonance imaging revealed a tumor around the clavicle extending to the anterior aspect of chest wall, which had low signal intensity on T1-weighted imaging and high signal intensity on T2-weighted imaging. The histologic findings were of a hyaline cartilage-like mass consisting of mature chondrocytes and an extracellular matrix. The histologic diagnosis of synovial chondromatosis was made. The present case is unusual in respect of the location and size of the tumor.