Monophasic Synovial Sarcoma

A 20-year-old female presents with increasing left thigh mass. She first noticed the mass five years ago with slow progression but recently rapidly increased in size. Previous treatment was unremarkable.

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Image 1: She had a bulging mass located medially in the left upper thigh which was tough and immobile on palpation and indolent. Neither sensory nor motor deficit were detected on physical examination. She denied any history of trauma or infection. Laboratory tests reveal normal results.

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Images 2: Ultrasound scan shows a large, relatively well-defined hypoechoic mass within muscle layer (caliper). The mass is heterogeneous in nature with irregular border, peripheral calcification and areas of necrosis (star). The mass also shows infiltration to the adjacent subcutaneous tissue. No evidence of vascular invasion.

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Images 3: Ultrasound scan shows a large, relatively well-defined hypoechoic mass within muscle layer (caliper). The mass is heterogeneous in nature with irregular border, peripheral calcification and areas of necrosis (star). The mass also shows infiltration to the adjacent subcutaneous tissue. No evidence of vascular invasion.

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Image 4: Lateral radiography of the upper left thigh shows a soft-tissue mass with punctuate curvilinear calcification (arrow) laterally without obvious underlying bone erosion.

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Image 5: Common femoral angiogram shows hypervascular soft-tissue mass with a fine network of tumor vessels and inhomogeneous capillary blush (arrow) which is supplied from the profunda femoris artery. Note the compression and spasm of the superficial femoral artery (arrowhead). (Catheter tip is in the common femoral artery).

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Image 6: Sagittal and coronal T1 weighted MR images show an 8 cm x 9 cm x 10 cm well-defined, heterogeneous soft tissue tumor (M) which is hypo-to-intermediate signal intensity in the anterior left upper thigh with extensive subcutaneous tissue invasion (IN). Intravenous contrast-enhanced T1W shows heterogeneous predominant enhancement of the mass, reflecting the intermixture of nonenhancing necrotic, cystic or hemorrhage, and enhancing solid regions. On T2-weighted image, the mass contains strikingly hyperintense cystic areas (star) with irregular septa of intermediate signal intensity. Arrows indicate edema of the adjacent tissue. Note the peripheral rim of hypointensity on both T1 and T2 weighted images represent calcification (Ca) which is proved on X-ray.

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Image 7: Histopathological study confirms the diagnosis of monophasic synovial sarcoma, fibrous type.

Diagnosis: Monophasic synovial sarcoma

Discussion: Synovial sarcoma represents only 5 percent of malignant soft tissue sarcomas, but it is one of the most common soft tissue sarcomas in younger adult patients (15 to 35 years). Although the name of the lesions suggests an articular process, and although this tumor is often found near a joint, 90 percent of SS do not originate from a joint. Rather, as with all SS, the tumor is named by the predominant histologic differentiation, in this case tumor cells that resemble synovioblastic cell.

There are three main subtypes of synovial sarcoma: biphasic, monophasic and poorly differentiated, among these monophasic is the most common (50 percent to 60 percent). Most occur in the lower extremity, especially at or distal to the knee. However, there is a broad spectrum of locations including head, neck, trunk, lung, esophagus, intestine, mediastinum and retroperitoneum. Synovial sarcoma is an intermediate-to-high grade neoplasm with extensive metastatic potential. The major sites of metastatic spread are lungs, less often, lymph node, bone and bone marrow. The clinical course of SS is characterized by a high rate of local recurrence and metastatic disease. Estimated five-year survival rare ranges from 36 percent to 76 percent, at 10 years it is from 20 percent to 63 percent

.

Clinically, synovial sarcoma appears as deep-seated, painless, slowly growing masses. Patients with SS usually present with a palpable soft-tissue mass or swelling. The long duration of symptoms and initial slow growth may simulate those of or give a false impression of a benign process.

A definitive diagnosis can only be established by an adequate tissue biopsy, but radiological investigations may be useful to characterize this tumor. Radiographs appear normal in approximately 50 percent of cases of SS, particularly those with small lesions. SS detected at radiography typically appear as nonspecific, round to oval juxtaarticular soft-tissue masses. Calcification is identified in up to 30 percent of SS at radiography. These calcifications are often eccentric or peripheral within the soft-tissue mass and nonspecific in appearance. Involvement of underlying bone is common seen as extrinsic erosion of bone or periosteal reaction has been reported in 11 percent to 20 percent of SS. The bone erosion often has an indolent nonaggressive appearance on radiographs, which can lead to misinterpretation of the lesions as representing a benign process. Angiographic descriptions of SS are limited with common findings are hypervascular and displacement of native vessels.

The ultrasound appearance of SS has not been extensively reviewed. Common findings are focal, nodular, round or lobulated, solid mass but hypoechoic soft-tissue mass is suggestive of a more indolent, less aggressive process. Doppler US studies would be expected to demonstrate vascularity in the areas of viable tumor. Any large (> 5 cm), solid, nonfatty, soft-tissue tumor should be considered sarcoma unless proven otherwise by biopsy.

The most common CT appearance of SS is that of a heterogeneous deep-seated soft-tissue mass with attenuation similar to or slightly lower than that of muscle, representing necrosis or hemorrhage areas. SS frequently demonstrates a multinodular morphology on CT scans. Contrast-enhanced CT shows heterogeneous enhancement in 89 percent to 100 percent of cases. This feature is helpful for distinguishing those SS that initially appear as a cystic lesion or hematoma on precontrast images, as the heterogeneous enhancement pattern excludes these diagnoses. Nodular areas of enhancement may also be seen in these lesions. CT is also useful for detecting calcification and bone involvement.

With its superior contrast resolution, MR imaging is the optimal radiologic modality for assessing the extent and intrinsic characteristics of SS for staging and diagnosis. On T1 weighted MRI, SS typically appears as a prominently heterogeneous multilobulated soft-tissue mass with signal intensity similar to or slightly higher than that of muscle. This signal heterogeneity has been described as the triple sign by Jones and co-workers, represented by intermixed areas of low (calcified or fibrotic collagenized regions), intermediate (mixture of cellular elements) and high signal intensity (hemorrhage or necrosis) on long repetition time images. Contrast-enhanced MRI can be particularly important for distinguishing SS with predominantly cystic characteristics with standard T1 and T2 weighted sequences.

As with many primary malignant soft-tissue neoplasms, local control of SS is primarily achieved with surgery. The current treatment of choice is wide local excision (removal of the tumor, its pseudocapsule and a normal cuff of surrounding tissue). The surgical margins should be closely evaluated to determine the need for adjuvant therapy. Amputation should be reserved for those cases in which gross resection of the tumor and preservation of a functional limb is not possible. The role of adjuvant therapy remains controversial. Chemotherapy has been used to treat metastatic or residual disease. The agents employed are combinations of adriamycin, cisplatin, vincristine, doxorubicin, ifosfamide. Radiation therapy plays an important role in the treatment of marginally resected tumors. Imaging features associated with a poorer outcome include a large tumor size of > 10 cm, absence of calcification and hemorrhage appearance.

Disclosures:

1. Mark D. Murphey, Michael S. Gibson, Bryan T. Jennings, Ana M. Crespo-Rodriguez, Julie Fanburg-Smith, Donald A. Gajewski. Imaging of Synovial Sarcoma with Radiologic-Pathologic correlation, Radiographics 2006; 26: 1543-1565, RSNA.

2. Ruggiero A. Synovial Sarcoma. Orphanet encyclopedia, March 2004

3. Anil T. Ahuja et al. Expert differential diagnosis ultrasound, 2010, Amirsys.

4. B.J. Manaster, David A. May, David G. Disler. Neural and synovial tumors, Musculoskeletal Imaging the requisites third edition 2007, Mosby Elsevier.

5. P.J. O’Sullivan, A.C. Harris, P.L. Munk. Pictorial review Radiological features of synovial cell sarcoma. The British Journal of Radiology, 81 (2008), 346-356.