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Synovial sarcoma - Foot and Ankle

Summary

Synovial sarcoma is the most common malignant soft tissue sarcoma in the foot, accounting for 18-22% of all such tumors. (9) In some series it is the single most common sarcoma of any type in the distal lower extremity.

Synovial sarcoma occurs in the second through fifth decades, with the average age of incidence around 28 years.
The presentation of synovial sarcoma is variable and may mimic a benign process such as ganglion cyst. The patient may have a mass that has been present for months, years, or even decades, with slow growth and little or no symptoms. There may have been recent rapid growth of a lesion that has been present for years without apparent change. Conversely, some of these sarcomas may be very painful from the outset. The average duration of symptoms before diagnosis is 21 months.
MRI findings are "indeterminate" as defined previously, with intermediate or low signal intensity on T1 sequences and high signal intensity on T2 sequences.
Both chemotherapy and radiotherapy have been shown to have a positive effect on survival.
Complete Information on this Tumor
Introduction and Definition: 

Synovial sarcoma is the most common malignant soft tissue sarcoma in the foot, accounting for 18-22% of all such tumors. (9) In some series it is the single most common sarcoma of any type in the distal lower extremity. This tumor deserves extra attention and study for several reasons. Among these are this tumor's potential for slow, painless growth, its peak incidence in young patients, and the serious consequences of delay in diagnosis.The most common location is the leg, ankle, or foot. The lesion is usually deeply seated, firm, and painless, but small superficial lesions are also seen. The tumor is firm to exam and does not transilluminate. Metastasis may occur to regional lymph nodes and these should be included in the physical examination.

Incidence and Demographics: 
Synovial sarcoma occurs in the second through fifth decades, with the average age of incidence around 28 years.
Symptoms and Presentation: 

The presentation of synovial sarcoma is variable and may mimic a benign process such as ganglion cyst. The patient may have a mass that has been present for months, years, or even decades, with slow growth and little or no symptoms. There may have been recent rapid growth of a lesion that has been present for years without apparent change. Conversely, some of these sarcomas may be very painful from the outset. The average duration of symptoms before diagnosis is 21 months.

X-Ray Appearance and Advanced Imaging Findings: 
Imaging studies are not adequate to distinguish this tumor from benign soft tissue masses. Plain radiographs are still useful and may show the invasiveness and the stippled calcification some synovial sarcomas have. MRI findings are "indeterminate" as defined previously, with intermediate or low signal intensity on T1 sequences and high signal intensity on T2 sequences. Axial imaging may reveal this lesion's potential to invade and destroy adjacent bones or soft tissues, but the tumor may appear well circumscribed. Most lesions present in stage II which indicates it has spread beyond the compartment of origin. Imaging of regional lymph nodes should be included in the MRI. examination.
Differential Diagnosis: 
Plantar fibroma can be surprisingly large and aggressive. Biopsy all soft tissue tumors greater than 2 or 3 cm in the foot unless the diagnosis is otherwise established with certainty.
Histopathology findings: 
Synovial sarcoma (SS) was named in 1934 by Sabrazes based on what appeared to be synovial tissue on light microscopy, However, the name is misleading and bears no relation to the origin of the tumor. The misapplied name continues to lead to mistaken assumptions about the location and behavior of the tumor. Recent cDNA microarray based studies found that the gene expression profile of synovial sarcoma is closely related to neural crest-derived malignant peripheral nerve sheath tumor. High grade, monophasic, poorly differentiated synovial sarcoma may appear to be a “small round blue cell tumor”, a group of tumors which includes Ewings/PNET, rhabdomyosarcoma, lymphoma, and others. Final diagnosis requires immunohistchemical staining analysis. However, immunohistochemical markers such as EMA and cytokeratin that are considered to be the most specific for SS may be absent. Vimentin is typically positive in synovial sarcoma. EMA and Cytokeratin are usually positive in synovial sarcoma. S-100 may be positive or negative in synovial sarcoma. On light microscopy, synovial sarcomas may be monophasic fibrous and biphasic. The monophasic type may appear to be a mass of small round blue cells, or more fibrous with spindle shaped cells. The biphasic type is of fibrous areas with clefts or spaces or areas with epithelial cells.
Treatment Options for this Tumor: 
Surgical resection with a wide margin remains the cornerstone of treatment. Both chemotherapy and radiotherapy have been shown to have a positive effect on survival. In one series, ten of 12 patients who had surgical treatment for synovial sarcoma in the foot required either a below-knee or a Chopart amputation.
Outcomes of Treatment and Prognosis: 
Overall prognosis of synovial sarcoma is only fair. Approximately 50 to 60% of patients will be free of disease at 5 years. There is an inverse correlation between prognosis and age at presentation. Distal lower extremity location may be a positive prognostic factor. Negative prognostic factors include large tumor size, high histologic grade, and metastasis at presentation.
Special and Unusual Features: 
Recent data has shown that synovial sarcoma displays two distinct types of chromosomal translocations t(X;18;p11;q11), named fusion type SYT-SSX1 and SYT-SSX2.Fusion type seems to have a significant impact on disease course and survival. In on study, Median and 5-year overall survivals for the SYT-SSX1 and SYT-SSX2 groups were 6.1 years and 53%, and 13.7 years and 73%, respectively.
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