Age / Sex : 24 / M

Age / Sex :
24/Male

Chief complaint :

Intermittent pain in the posterior aspect of the knee

Discussion

Findings:

Plain radiographs showed a densely ossified mass which seemed to abut on the posterior aspect of the proximal tibia and two small radiodense masses in the suprapatellar pouch and the Hoffa’s fat pad were initially missed on the radiograph.

CT scan was performed to further evaluate, which showed a large, well-circumscribed calcified mass extending into the popliteal fossa with another small mineralized masses

Differential Diagnosis:

The combined radiographic and clinical differential diagnosis included a parosteal osteosarcoma as well as myositis ossificans and tumoral calcinosis, with parosteal osteosarcoma being preferentially considered in the differential diagnosis. However, the identification of another small intra-articular loose bodies markedly limits the differential diagnosis. Based on the CT findings, we placed synovial chondromatosis on the top of the differential diagnosis rather than mineralizing malignant tumor such as parosteal osteosarcoma.

Diagnosis:  

Synovial chondromatosis

Discussion:

Radiographic evaluation will be unrewarding if the loose bodies lack calcification or ossification and may be visible just as indistinct soft tissue masses. However, when mineralization occurs, radiographs reveal radiopaque, round loose bodies within the joint or periarticular area and the diagnosis can be established preoperatively. CT is useful in identifying the lesion in its early stages when there is insufficient mineralization to be documented in plain radiographs. MR imaging findings are more variable owing to the extent of mineralization and ossification of the chondral bodies. CT and MR imaging depict the extent of the synovial disease and lobular growth. The classical imaging appearance of synovial chondromatosis is multiple, oval, well-defined, intra-articular and homogeneous calcified bodies which are typically distributed evenly throughout the joint. These calcifications frequently show a pathognomic appearance of ring-and-arc, popcorn-like, or feathery pattern of mineralization. In addition, chondral bodies may also progress to further maturation and enchondral ossification with a peripheral rim of cortex and inner trabecular bone. In rare cases, the individual chondral bodies coalesce to form a larger, conglomerate, mineralized mass. Edeiken and coworkers described 10 patients with a giant synovial chondromatosis showing osteocartilagenous bodies varying in size from 1 cm to even 20 cm, with the knee involved in five of the cases.7 They suggested that on the basis of radiologic findings, the giant solitary chondroma is formed by the fusion of multiple synovial chondromas or by continued growth of a solitary synovial chondroma into a large, well-circumscribed calcified mass, which was similar to our case. Occasionally, giant synovial chondromatosis and the classical type of synovial chondromatosis may occur concurrently in the same region as our case.

References:

1. Norman A, Steiner GC. Bone erosion in synovial chondromatosis. Radiology 1986;161:749-52.

2. Villacin AB, Brigham LN, Bullough PG. Primary and secondary synovial chondrometaplasia: histopathologic and clinicoradiologic differences. Hum Pathol 1979;10:439-51.

3. Murphey MD, Vidal JA, Fanburg-Smith JC, Gajewski DA. Imaging of synovial chondromatosis with radiologic-pathologic correlation. Radiographics 2007;27:1465-88.

4. Edeiken J, Edeiken BS, Ayala AG, Raymond AK, Murray JA, Guo SQ. Giant solitary synovial chondromatosis. Skeletal Radiol 1994;23:23-9.