Extraskeletal Osteosarcoma of Mediastinal Origin

Mediastinal extraskeletal osteosarcoma (ESOS) with cardiac involvement is extremely rare and aggressive. The authors describe a 56-year-old male individual presenting with chest tightness and dyspnea. Imaging revealed a large pericardial mass compressing the right atrium. Surgical resection was performed, and histopathology findings confirmed high-grade ESOS. The patient underwent adjuvant radiation therapy and chemotherapy. At 6 months, pulmonary metastases were detected, prompting treatment adjustment. At 11-month follow-up, the patient remained clinically stable. This case underscores the utility of multimodality imaging and the diagnostic and therapeutic challenges of this rare malignancy. Keywords: Cardiac, Oncology © RSNA, 2026