by John Salamone, DPM¹ , Martha A. Anderson, DPM²

Podiatry Internet Journal 2 (7):1

Synovial sarcoma is a rare soft tissue neoplasm commonly found in the lower extremity. It is included in the differential diagnosis of all soft tissue masses of the foot and ankle. It has a particular predilection for the lower extremity. Early diagnosis and staging with definitive treatment provides the highest probability in preventing metastasis and local recurrence. A case report of synovial sarcoma masquerading as sesamoiditis is presented. Clinical, MRI and histopathologic findings are also presented.

Synovial sarcoma was first described by Simon in 1865 and termed synovial sarcoma in 1934 by Sabrazes, et al. The incidence of synovial sarcoma is 2.5 per 100,000 people annually.[6] It accounts for 8-10% of all soft tissue sarcomas in the body and 6% of all foot and ankle soft tissue tumors.[6] Synovial sarcoma is the most common malignant soft tissue tumor in the lower extremity, followed by epithelioid sarcoma and malignant fibrous histiocytoma. Fourteen percent of all synovial sarcomas present in the foot.[3] Metastasis varies from 25-65% over a five year period depending on the grade and extent of the sarcoma. It most commonly presents in young to middle-aged adults. Peak incidence occurs between the second and fifth decades. [1]

Recurrence of the tumor is uncommon. Anatomic location has not been found to be an independent prognostic factor for recurrence. However, a positive surgical margin has double the risk of local recurrence. [2] For this reason it is important to identify this tumor early and pursue adequate and aggressive treatment with follow up.

Case Report

A 62 year old Caucasian male presents with a 10 year history of pain under the first metatarsophalangeal joint. He has no other symptoms. He is employed as a flooring specialist. His foot is extremely painful while working. He provided an account of blunt trauma to the region that he felt to be contributory. He has no other symtoms with the exception of pain to the tibial sesamoid and flexor hallucis brevis tendon of the left foot. His pain is marginally relieved with over the counter non-steroidal anti-inflammaties. Radiographs of the left foot were unremarkable in appearance and no sign of a tumor is appreciated. (Fig. 1) He was initially treated conservatively with padding, immobilization in a surgical shoe, and corticosteroid injections without any improvement.

Figure 1 Initial foot radiograph with no pathology appreciated in the region of the sesamoids.

Lab studies and advanced imaging was ordered. Complete blood counts, erythrocyte sedimentation rate, C-reactive protein, serum uric acid, Rheumatoid factor, and anti-nuclear antibody testing were normal.

The initial MRI showed a non-specific soft tissue mass with low signal intensity on T1 weighted imaging and high signal intensity on T2 and STIR sequences measuring 1.4cm x 1cm x 0.8cm just plantar and proximal to the sesamoid apparatus in the left foot. (Fig. 2)

Figure 2   The initial sagittal MRI, without contrast, demonstrating a soft tissue tumor just proximal to the sesamoid.  The mass measures 1.4cm x 1cm x 0.8cm.

Given a prior history of trauma, granulomatous reaction was considered to be high on the differential diagnosis. Other benign and malignant soft tissue masses were considered to be less likely.

After magnetic resonance imaging (MRI) was completed the patient was lost to follow up for approximately eighteen months.

After eighteen months, the patient presented with continued pain to the plantar aspect of the first metatarsophalangeal joint. Physical exam findings at this examination were unchanged. Although no palpable masses were appreciated, exploration and biopsy were advised. Due to an upcoming knee replacement, his foot surgery was deferred. Just prior to foot surgery, some 24 months after his initial presentation and in preparation for upcoming surgery, follow up MRI and CT scan were ordered (Figures 3, 4).

Figure 3   The follow up MRI with gadolinium contrast and increased enhancement of the soft tissue mass.  The mass now measured slightly larger at 1.8cm x 1.6cm x 1.1cm.

Figure 4   CT scan showing the absence of any osseous involvement of the tumor.

Histopathology

Frozen section samples were inconclusive. The specimen received was described as a malignant spindle cell neoplasm with a marbled growth pattern. Some areas are darkly stained with more cellular and alternating areas being lightly stained and less cellular. Tumor nuclei were ovoid in appearance with scattered mitotic figures. Margins of the tumor were positive.

The pathology slides were sent to an outside facility for confirmation of the diagnosis. Immunohistochemical staining was strongly positive for Vimentin and BCL-2. The tumor also stained positive for Epithelial Membrane Antigen (EMA) and S-100 protein. Tumor cells did not stain positive for Cytokeratin 5/6. With this information, the neoplasm was defined to be a grade 2/3 monophasic fibrous synovial sarcoma. (Fig. 5)

Figure 5  Histological slide demonstrating monophasic fibrous type synovial sarcoma grade 2/3.

Discussion

The presentation of synovial sarcoma in this case was somewhat atypical in that the tumor was small, showed homogenous signal intensity on MRI, and increased in size minimally over two years. In contrast, most sarcomas have somewhat aggressive imaging characteristics such as irregular borders, heterogeneous signal within the lesion, diffuse enhancement with gadolinium contrast material, and an infiltrative pattern. Less aggressive lesions have been shown to be better defined. [4,7]

It is important to keep in mind that soft tissue masses in the foot or ankle may undergo malignant transformation. [5] In this case, it is probable that the lesion was malignant at the time of the patient’s initial presentation. In all cases the definitive diagnosis is strictly pathologic and biopsy should therefore not be delayed.

Pathologic diagnosis is based on histologic exam with the aid of special immunohistochemical staining techniques. Vimentin stains intermediate filaments and is typically positive in synovial sarcoma. BCL-2 is an apoptosis gene and is positive in many neoplasms. EMA and Cytokeratin 5/6 are epithelial markers and are usually positive in synovial sarcoma. S-100 is a marker of neural differentiation and can be positive or negative in synovial sarcoma.

Synovial sarcomas have two main histologic types, monophasic fibrous and biphasic. The monophasic type has a fibrous appearance on histologic exam with spindle shaped cells and is commonly positive for S-100. The biphasic type is composed of more cuboidal or columnar epithelial cells and is usually negative for S-100.

In addition, synovial sarcomas are graded from 1 to 3 based on the amount of differentiation. Grade 1 is highly differentiated, grade 2 being moderately differentiated, and grade 3 poorly differentiated. (Table 1) The tumor node metastasis (TNM) classification is also applied to patients diagnosed with synovial sarcoma.

Histologic Grade	Findings
1	Well differentiated cells within the neoplasm
2	Moderately differentiated
3	Poorly differentiated

Table 1   Histologic grading for Synovial sarcoma.

The neoplasm presented here was not tested for the typical SYT translocation found in many synovial sarcomas which fuses a portion of chromosome 18 to the X chromosome. The specific translocation in synovial sarcoma is t(X;18)(p11.2;q11.2).

A thorough history and physical is important when making a diagnosis. Lab testing, radiographs and advanced imaging techniques are used to help in the primary diagnosis. Surgical planning should include biopsy, local or wide excision and/or amputation. The extended workup of these tumors is often of adjunctive value with the definitive diagnosis being determined by surgical pathology. The biopsy technique utilized depends largely on the level of suspicion by the surgeon. In cases where lesions are palpable or visible clinically, suspected to be benign, or where MRI reveals more benign findings, it would be appropriate to totally excise the lesion.

The patient was referred to an orthopedic oncologist for further management after confirmation of the synovial sarcoma diagnosis. Chest radiograph and CT scans of the chest, abdomen, and pelvis were found to be negative for metastasis. He underwent wide resection which consisted of partial first and second ray amputation of the affected foot to assure that all margins of the tumor were negative for neoplastic cells.

This second specimen was also sent for pathologic confirmation to assure that negative margins were present. This was found to be the case and no further surgical intervention was required.

The patient is now fully ambulatory with accommodative inserts and stump filler in extra depth shoes. To date, he is pain free without signs of metastasis. There has been no local recurrence of the sarcoma.

The patient will undergo serial chest x-rays every 3 months. The patient did not undergo adjuvant chemotherapy since the surgical margins were negative and the tumor was felt to be slow-growing.

Conclusion

Synovial sarcoma is a rare soft tissue tumor that may be encountered in clinical practice. It is the most common malignancy in the foot and ankle. The death rate from synovial sarcoma is 2%. [5] If synovial sarcoma is properly and promptly treated it will lead to less complications, lessen the degree of recurrence and decrease the risk of metastasis and premature death.

References:

1. Bos, GD, Esther, RJ, and Woll, TS. Foot Tumors: Diagnosis and Treatment. J Am Acad Orthop Surg 2002; 10:259-270.
2. Ferguson, PC. Surgical considerations for management of distal extremity soft tissue sarcomas. Curr Opin Oncol 2005; 17:366-369.
3. Johnston, MR. Epidemiology of soft-tissue and bone tumors of the foot. Clin Podiatr Med Surg 1993; 10:581-607.
4. Kransdorf, MJ. Begnign Soft Tissue Tumors in a Large Referral Population: Distribution of Specific Diagnoses by Age, Sex, and Location, Am J Roen 1995; 164:395-402.
5. Mercuri, M and Casadei, R. Tumours in the foot. Foot and Ankle Surgery 2002; 8:175-190.
6. Scully SP, et al. Synovial Sarcoma of the Foot and Ankle. Clin Orthop Rel Res 1999;364:220-226.
7. Woertler, K. Soft Tissue Masses in the Foot and Ankle: Characteristics on MR Imaging. Semin Musc Rad 2005; 3:227-242.

Special thanks to the pathology departments of Kaiser Permanente and Cleveland Clinic for their assistance in slide preparation and photography.

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Address correspondence to: Marth Anderson, DPM, Kaiser Permanente Department of Podiatry. 12301 Snow Rd. , Parma, OH 44130. EMAIL: andersm11@ccf.org 

¹Staff, Kaiser Permanete, Department of Podiatric Surgery, Cleveland, OH

²Third Year Resident (PGYIII), Cleveland Clinic/Kaiser Permanete Residency Program, Cleveland, OH

© Podiatry Internet Journal , 2007

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