Pericardial Synovial Sarcoma Masquerading as Hemangioma: A Diagnostic Challenge.

Pericardial synovial sarcoma (PSS) is a rare primary malignant tumor of the heart with an unclear prognosis. We present the case of a 26-year-old male patient with no significant medical history who presented with New York Heart Association (NYHA) Class II dyspnea and chest pain. Echocardiography and cardiac MRI revealed a large pericardial mass (93 × 70 × 45 mm) with hemorrhagic effusion and imaging features suggestive of hemangioma, including well-defined vascular channels and contrast enhancement. Histopathological analysis following thoracotomy showed spindle cell proliferation without classic features of malignancy (e.g., nuclear atypia and high mitotic activity), supporting the initial diagnosis of spindle cell hemangioma. However, six months later, a recurrent mass excision and immunohistochemistry (IHC) confirmed SS (transducin-like enhancer of split 1/FMS-like tyrosine kinase 1 (TLE1/FLT1) positive). Surgical resection was attempted but was not feasible due to the extensive involvement of critical cardiac structures. The patient was started on chemotherapy with ifosfamide and doxorubicin but succumbed to systemic complications within a year. This case underscores the diagnostic challenge of PSS and highlights the critical role of IHC and molecular diagnostics in distinguishing it from benign mimics, even when initial histopathology is inconclusive.