Differential Diagnosis of Synovial Sarcoma in the Pelvis
| Tumor | Cytomorphologic Features | Immunohistochemistry Profile and Cytogenetics |
|---|---|---|
| Malignant peripheral nerve sheath tumor | Hypocellular and hypercellular areas with cells showing wavy nuclei, nuclear buckling/kinking/twisting, and nuclear pseudoinclusions26 | S100 protein27, SOX10 |
| Leiomyosarcoma | Spindle-shaped cells arranged in intersecting fascicles having blunt cigar-shaped nuclei with paranuclear vacuolations and abundant eosinophilic cytoplasm26 | Smooth muscle actin, desmin, and h-Caldesmon; can show focal expression of epithelial membrane antigen and keratin in a dot-like pattern27 |
| Solitary fibrous tumor | Spindle-shaped cells with ovoid vesicular nuclei arranged in a patternless way, rare mitotic figures, varying amounts of collagenous stroma, prominent thin-walled hemangiopericytic vessels26 | Diffuse expression of CD34,26 diffuse nuclear expression of STAT626; one-third express AE1/AE3; nuclear expression of FLI1 |
| Ewing sarcoma/primitive neuroectodermal tumor | Isolated or sparsely clustered round to oval uniform small cells with central nuclei, rosette formation28 | Positive periodic acid-Schiff stain, strong membranous immunoreactivity for CD99,18 caveolin-126 Cytogenetic analysis for t(11;22) for confirmation of Ewing sarcoma14 |
| Fibrosarcoma | Diagnosis of exclusion, spindle cells arranged in a herringbone pattern, can be pleomorphic, produces intercellular collagen2 | Negative for cytokeratin and epithelial membrane antigen2 |
| Sarcomatoid carcinoma and Müllerian adenosarcoma | More pleomorphic than synovial sarcoma2 | Diffuse cytokeratin positivity2 |
| Sarcomatoid mesothelioma | Larger and less uniform nuclei,2 single cells and loose aggregates, short spindle-shaped cells without microvilli30 | Calretinin, podoplanin (D2-40), WT1, CK5/6, mesothelin31 |
| Synovial sarcoma | Mixed population of cohesive tissue fragments and scattered cells, tissue fragments contain thin branching capillaries, mitosis and mast cells present, sometimes admixed with epithelial-like structures20,21 | Epithelial membrane antigen, CK7,24 CK19,24 BCL2 (nearly 100% of synovial sarcoma cases), CD56 (nearly 100% of synovial sarcoma cases),25 CD99 (60% of synovial sarcoma cases),20 S100P (30% of synovial sarcoma cases),20 TLE1(most sensitive and specific)29 Cytogenetic analysis for detection of t(X;18)(p11.2;q11.2) translocation for confirmation of synovial sarcoma24,28,32 |