Teaching Case

A 37-year-old male reported experiencing slight movement restriction in his right wrist for the past year. He had no history of trauma. Physical examination revealed diffuse oedema in the right wrist, without any visible redness or tenderness.

On plain radiographs (Figures 1a and 1b), the AP and lateral views of the right wrist show vague radiodense soft tissue masses with multiple punctate calcifications involving the radiocarpal, ulnocarpal, and carpometacarpal joint spaces along the volar and dorsal aspects. No evidence of adjacent carpal bone erosion was noted.

Axial and coronal images of the CT of the right wrist with soft tissue window (Figures 2a and 2b) and bone windows (Figures 2c and 2d) show multiple, fairly defined intra-articular hypodense lobulated soft tissue masses with calcified loose bodies within the radiocarpal, ulnocarpal, and carpometacarpal joint spaces, involving both the flexor and extensor compartments.

On coronal STIR and axial T2-weighted images (Figures 3a and 3c), multiple fairly defined intra-articular extensive T2/STIR hyperintense lobular masses with multiple subcentimetric hypointense areas are noted. These areas show blooming on GRE (Figure 3b), suggesting synovial loose bodies, within the carpal and wrist joint spaces, extending into the extensor and flexor compartments of the right wrist and closely abutting adjacent tendons. The same lesions show intermediate signal intensities on coronal T1 images (Figure 3d).

A benign, rare entity called primary synovial osteochondromatosis is characterised by synovial metaplasia and hyperplasia, with frequent observations of cartilaginous nodules releasing loose bodies into the synovial cavity. This condition is also known as Reichel’s syndrome or Reichel–Jones–Henderson syndrome [1]. Synovial chondromatosis presents as cartilaginous foci in tendon sheaths, bursae, and synovial membranes. Initially, these cartilaginous foci develop as sessile structures with a strong synovial attachment, eventually becoming pedunculated and breaking free to become free intra-articular or periarticular loose bodies. After becoming free in the joint, they continue to grow thanks to the nourishment provided by the synovial fluid and eventually either reconnect to the synovium or are reabsorbed [2]. These loose bodies give the synovium a cobblestone appearance.

Intra-articular pathology is typical, but extra-articular cases have also been reported, typically involving tenosynovial structures. Primary synovial chondromatosis typically affects adults, predominantly men, in the third to fifth decades of life [2]. The most frequently involved joint is the knee, followed by the hip, elbow, and shoulder. The wrist is seldom affected. Men are more likely than women to be afflicted during the third to fifth decades of life [3]. This contrasts with secondary synovial chondromatosis, which occurs when underlying joint pathology, such as trauma (either a single traumatic event or repeated microtrauma), osteochondritis dissecans, advanced osteonecrosis, or Charcot neuropathic joint, results in synovitis and/or articular destruction. Secondary synovial chondromatosis results from mechanical injury to the intra-articular hyaline cartilage and typically affects individuals in their 50s and 60s [2].

Radiographs of primary synovial chondromatosis typically reveal several intra-articular calcifications, evenly distributed throughout the joint in 70%–95% of cases. Ring-and-arc or punctate calcifications frequently have a pathognomonic appearance, being numerous and quite similar in shape. Other features include joint effusion and extrinsic erosion of joints [3]. Radiographs can be normal in 5%–30% of primary intra-articular synovial chondromatosis cases. Arthrography, typically followed by CT or MR imaging, often depicts diagnostic features, with multifocal intra-articular chondral bodies seen as numerous circular filling defects. In secondary synovial chondromatosis, intra-articular loose bodies are fewer in number and variable in size, and radiographs show underlying joint pathology [3].

CT is particularly helpful in identifying unique ring-and-arc or punctate mineralisation. Because CT allows for cross-sectional imaging, it is also the most effective method for assessing extrinsic bone degradation [4]. On MRI, T1-weighted images show the signal intensity of primary synovial chondromatosis as lobulated, homogeneous, intermediate, intra-articular, and indistinguishable from the signal intensity of muscles. On T2-weighted images, the signal intensity is high, with focal areas of low signal intensity noted in all pulse sequences [4]. On GRE, calcified loose bodies show blooming.

Given the presence of synovial proliferation and intra-articular loose bodies, a differential diagnosis could include lipoma arborescens, a rare entity in which the normal synovium is replaced by hypertrophied villi with marked deposition of mature lipocytes within them, manifesting as a characteristic fat signal intensity or density. Another consideration is tenosynovial giant cell tumour, a group of fibrohistiocytic tumours that arise from synovium, bursae, or tendon sheaths, which present as more confluent masses with a diffuse characteristic low intensity on MRI. A malignant lesion should be taken into account throughout the differential diagnostic process, including low-grade intraosseous chondrosarcoma extending into a joint. Findings from an MRI aid in differentiating synovial chondrosarcoma, as it is unusual for synovial chondromatosis to cause marrow invasion [3].

The most effective treatment for synovial osteochondromatosis in patients with ongoing symptoms is total synovectomy, which entails the removal of any loose cartilaginous nodules [5]. According to research, incomplete excision is likely the reason for recurrence following resection, so surgeons should ensure a comprehensive synovectomy is performed [5]. Moreover, monitoring the condition following surgery is helpful, even if there is little chance of malignant degeneration and recurrence.