Rapidly Progressive Primary Pleural Myxoid Sarcoma: Diagnostic Challenges and the Critical Role of FDG PET-CT Staging

A 43-year-old agricultural labourer with a 20-year history of occupational pesticide exposure presented with a 2-month history of progressive right-sided chest pain. Imaging revealed a massive right pleural-based myxoid spindle cell tumour (28.1 × 18.9 × 20.5 cm). Whole-body ¹⁸F-fluorodeoxyglucose (FDG) PET-CT demonstrated an extensively metabolically active primary pleural mass with widespread metastatic dissemination involving pulmonary, nodal, skeletal, gluteal soft tissue, paravertebral, and suspected cerebral sites, establishing Stage IV disease at initial presentation. Histopathology showed a myxoid spindle cell sarcoma with extensive necrosis. Immunohistochemistry demonstrated vimentin and C-KIT positivity with focal synaptophysin expression; a comprehensive negative panel (cytokeratin, calretinin, D2-40, STAT6, TLE-1, DOG-1, S-100, desmin) excluded carcinoma, mesothelioma, solitary fibrous tumour, synovial sarcoma, and gastrointestinal stromal tumour. The pathological differentials were extraskeletal myxoid chondrosarcoma versus primary pulmonary myxoid sarcoma, with molecular confirmation pending. This case highlights the critical diagnostic and staging value of FDG PET-CT in rapidly progressive primary pleural sarcomas.