Synovial cell sarcomas account for 7 percent of soft tissue sarcomas. These lesions typically are found in the lower extremity (60 percent of cases); the knee, ankle and foot are the most common locations. Males are more frequently afflicted than females, and the peak age of incidence is 15 to 35 years. [1,2] The tumor is most frequently periarticular in location, arising from the tendon, tendon sheath, bursa or external capsule of the joint. Less than 10 percent of the lesions are intra-articular. [2,3]
The clinical presentation of synovial cell sarcoma is most frequently that of a painful mass, in distinction from other sarcomas, which are classically painless. [2,4] The symptoms are nonspecific, which accounts for the greater than 12-month duration of pain that the patient often reports at the time of seeking medical treatment. Although the tumor is typically slow growing, this delay in diagnosis probably contributes to the frequent incidence of metastases, most often to the lung (75 percent of cases with metastases), regional lymph nodes (15 percent) and bone (10 percent). Synovial cell sarcoma is the most common soft tissue sarcoma to metastasize to lymph nodes. 
On pathologic examination, the mass is typically 3 cm or larger and has a tan or grayish hue and a firm consistency. Cystic areas or calcifications may be noted. Although the lesions may grossly appear to be encapsulated, microscopic invasion of adjacent structures is visualized. Microscopically, a biphasic pattern is frequently noted, with alternating synovioblastic epithelial and spindle cell elements.  Immunochemical stains are positive for vimentin and keratin, similar to synovial tissue; however, direct proof of origin from existing synovial tissue, as opposed to development de novo, has not been demonstrated.
The classic plain film findings of synovial cell sarcoma are those of a soft tissue mass, which may be lobulated but often appears to be well demarcated from other tissue by a surrounding capsule.  Calcification occurs in 30 to 50 percent of cases; the radiographic appearance of calcification ranges from a fine, stippled calcification to dense, focal calcifications (Figure 1). Adjacent periosteal reaction is seen in 15 to 20 percent of cases, although cortical bone involvement is unusual.
Computed tomographic (CT) scanning is helpful in delineating the extent of the mass and its relation to adjacent soft tissues. CT increases the ability to detect calcification and periosteal reaction (Figure 2). The angiographic appearance is variable, ranging from the more common hypervascular lesions with tumor vessels to the less common hypovascular masses (Figure 3). [2,4] The radiologic differential diagnosis includes myositis ossificans, calcified hematoma, other soft tissue sarcomas (such as fibrosarcoma, rhabdomyosarcoma and liposarcoma), an inflammatory mass, a pseudoaneurysm and extraosseous osteosarcoma or chondrosarcoma.
Treatment and Prognosis
The standard surgical therapy is radical resection; amputation is necessary in many cases. Local resection is associated with a recurrence rate of approximately 45 percent within two years. Survival is greatest in young patients, when lesions are smaller than 5 cm at the time of diagnosis, and with histologically low-grade lesions. Overall, survival rates range from 25 to 40 percent at five years and from 10 to 15 percent at ten years. The prognosis is dismal when metastases are present, with adjuvant therapy of limited benefit. [1,2]
COPYRIGHT 1990 American Academy of Family Physicians
COPYRIGHT 2004 Gale Group