Laboratory Studies
Cytogenetic analysis aids the physician in detecting the specific chromosomal translocation between chromosome 18 and chromosome X—namely, t(X;18)(p11;q11). [25, 26, 27] This translocation produces the SYT-SSX1, SYT-SSX2, or SYT-SSX4 fusion gene. Identification of this anomaly is obtained by reverse transcriptase–polymerase chain reaction (RT-PCR) in tumor tissue (and possibly in blood), [7, 8, 28] with a sensitivity of 96% and specificity of 100%. Fusion transcripts can be detected with molecular diagnostic techniques in biopsy samples.
Fluorescence in-situ hybridization (FISH) is less expensive than RT-PCR. It has been suggested as a good method of first choice for synovial sarcoma (also referred to as synovial cell sarcoma). [28] This method has a lower sensitivity than RT-PCR does, but the results of the two methods are concordant in 76% of cases.
Aside from molecular diagnostic tests, no laboratory studies are specific for this diagnosis.
Plain Radiography
Plain radiographs may aid in the diagnosis. Synovial sarcoma typically produces a spotty calcification (snowstorm) within the matrix of the soft-tissue tumor that may be visualized on plain radiographs (see the image below).
Lateral radiograph depicts a synovial sarcoma of the dorsum of the hand. A small nodule, present for 5 years, rapidly enlarged to the present size over 2 months.
Computed Tomography
Computed tomography (CT) is used to confirm the presence of a mass, its size, and its location, but it is nondiagnostic. It also may detect secondary bony involvement, which is not uncommon with larger synovial sarcomas. Synovial sarcoma is a malignant disease; therefore, CT of the chest is mandatory to exclude metastatic disease.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is the investigation of choice for soft-tissue sarcomas. Low signal intensity is observed on T1-weighted MRI (see the first image below), and high signal intensity is observed on T2-weighted MRI (see the second image below). The signal from the matrix is fairly homogeneous unless calcification is present.
T1-weighted MRI depicts a synovial sarcoma of the dorsum of the hand. The tumor has low signal on T1 weighting.
T2-weighted MRI depicts a synovial sarcoma of the dorsum of the hand. The tumor has a heterogeneous signal on T2 weighting, indicative of a variable growth pattern.
Histologic Findings
The histologic picture of synovial sarcoma can be confused with those of many other round blue cell tumors. Macroscopically, the tumor is grayish-white and often has a greasy feel. Histologic features of synovial sarcoma are identical in children and adults.
Three types of synovial sarcoma have been described, as follows:
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In the monophasic type, there is a predominance of spindle cells, mixed with round cells (see the image below); cells are arranged in fascicles with a poorly defined cytoplasm; no glandular areas are present
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The biphasic type has a layer of columnar epithelium in addition to spindle cells; it consists of plump, round cells and spindle-shaped fibroblasts alternating with glandular-like areas that are lined by synovial-like cells and contain mucin
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A third type, called poorly differentiated, has numerous mitosis, high cellularity, and tumor necrosis
Although synovial sarcoma typically has a biphasic histology, this disease is often monophasic (lacking glandular differentiation), which produces the picture of a small, round blue cell tumor.
The histologic grade is determined by a score of the mitotic activity and tumor necrosis, ranging from grade 1 (differentiated) to grade 3 (poorly differentiated). Synovial sarcoma is very often associated with a grade of 2 or 3. [12, 6, 7, 29] Punctuate areas of calcification may be observed.
Staging
Staging requires local imaging with MRI. The most likely site of distant spread, the lungs, can be observed by means of CT. Synovial sarcoma is a high-grade lesion.
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Lateral radiograph depicts a synovial sarcoma of the dorsum of the hand. A small nodule, present for 5 years, rapidly enlarged to the present size over 2 months.
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T1-weighted MRI depicts a synovial sarcoma of the dorsum of the hand. The tumor has low signal on T1 weighting.
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T2-weighted MRI depicts a synovial sarcoma of the dorsum of the hand. The tumor has a heterogeneous signal on T2 weighting, indicative of a variable growth pattern.
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Although synovial sarcoma typically has a biphasic histology, this disease is often monophasic (lacking glandular differentiation), which produces the picture of a small, round blue cell tumor.
