Primary pulmonary artery synovial sarcoma: a case report.

BACKGROUND: Primary pulmonary artery synovial sarcoma (PPASS) is an extremely rare cardiac malignancy, often misdiagnosed preoperatively due to its nonspecific clinical and imaging features. This case report aims to enhance diagnostic recognition of this rare entity. CASE DESCRIPTION: A 35-year-old male presented with chest pain after activity for 1 month. Physical examination revealed stable vital signs and no significant cardiac murmurs. Laboratory tests showed negative immunofixation electrophoresis, unremarkable urinary light chains and coagulation function, and an N-terminal pro-B-type natriuretic peptide (NT-proBNP) level of 2,298 pg/mL. Transthoracic echocardiography (TTE) revealed an irregular solid mass (46 mm × 18 mm) at the pulmonary valve orifice, with a broad base and unclear border. Contrast-enhanced echocardiography showed mild perfusion within the mass. Cardiac magnetic resonance imaging and positron emission tomography/computed tomography (PET/CT) revealed atypical features [ill-defined borders and mild fluorodeoxyglucose (FDG) uptake], raising suspicion for malignancy. The patient underwent surgical resection of the cardiac tumor, pulmonary valvuloplasty, and tricuspid valvuloplasty. Intraoperatively, two distinct tumors were identified and resected. Postoperative pathology revealed a spindle cell tumor. Immunohistochemistry supported a diagnosis of biphasic synovial sarcoma, which was definitively confirmed by fluorescence in situ hybridization (FISH) demonstrating SS18 gene rearrangement. The Ki-67 index was 60%. Six months post-surgery, imaging revealed local recurrence and lung metastases, and the patient received two cycles of ifosfamide, pirarubicin, and mesna chemotherapy with good tolerance. CONCLUSIONS: This case highlights the diagnostic challenges of PPASS, which can mimic myxoma on echocardiography. A broad base, unclear border, and atypical contrast perfusion should raise suspicion for malignancy. Definitive diagnosis relies on histopathology and molecular detection of SS18 rearrangement.