Monophasic Synovial Sarcoma

Matthew P Schenker, MD - Case Coordinator
Karl Edwin Stien, MD - Radiology Discussion
David W Kindelberger, MD - Pathology Discussion
Pablo R Ros, MD, MPH - Attending Radiologist
Steven E Seltzer, MD - Attending Radiologist

March 24, 2003

Presentation

Imaging Findings

Coronal STIR images (fat saturated T2) show a multiloculated mass in the medial forearm. It is not clear which muscle group is involved. The mass does not seem to be abutting the cortex of the bone. Foci of high T2 signal within the mass suggest either a high fluid content (myxoid) or cystic structure. T2-weighted axial images indicate that the lesion is a single mass arising from the anterior compartment. Bone involvement is still not clear. Fat saturated T1-weighted axial images demonstrate faint peripheral enhancement following contrast administration and seem to indicate involvement of the bone. Cortical breakthrough is not clear.

Differential Diagnosis

Diagnosis

Discussion

The gross specimen is a wide, local soft tissue excision from the right arm. An expansile (12-cm) mass is located in the center of the muscle fibers, with adjacent areas of necrosis and hemorrhage. Cystic spaces were also noted. The tan-colored, fleshy areas represent the characteristic appearance of this tumor. Low-powered microscopy shows an extremely monomorphic population of spindle cells with high nuclear cytoplasmic ratio and relatively little intervening stroma. It is easier to see some of the cellular features at higher power, which demonstrates the tapering nuclei and scant cytoplasm. The mitotic activity in this tumor was determined to be high (up to 30 per 10 hpf).

Radiology Discussion:

Synovial sarcoma is the fourth most common sarcoma in the US, representing 8-10% of all cases. It typically affects persons aged 15-35 years, with a 3:2 male:female predominance. The most common presenting symptoms are an enlarging mass and pain (50%). Distant metastases occur in more than 50% of cases, and there is a high rate of local recurrence.

Synovial sarcoma typically occurs in the lower extremity (70%), often affecting the knee. It is also the most common malignant soft tissue tumor of the foot. Just 20-30% of cases affect the upper extremity. The tumor itself is usually centered in tendons, bursa, and joints; only 10% are intra-articular. The lesion is commonly slow-growing with well-defined margins, and can be mistaken for a benign etiology. Calcifications are visible in more than 30% of cases. While these are generally diffuse and punctate, increased coarse calcifications are associated with a better prognosis. Plain radiographs of the affected area are often normal unless calcifications are visible. If the bone itself is involved, a wide zone of transition or juxta-articular osteoporosis (probably secondary to disuse) may be noted. Computed tomography should show any calcification and may be used to evaluate the extent of the lesion, particularly involvement of the bone. Magnetic resonance imaging will typically show high T2 signal and intermediate signal on T1. More than 80% of lesions have an inhomogeneous appearance, and more than 70% are cystic. Diagnosis requires biopsy.

The differential diagnosis for synovial sarcoma includes chondrosarcoma, liposarcoma, malignant fibrous histiocytoma (MFH), osteochondroma/osteochondromatosis, osteosarcoma variants, and synovial osteochondromatosis.

Difficulty Level: 4th Year

References

Kaplan, et al: Musculoskeletal MRI. Philadelphia: WB Saunders; 2001.

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