Diagnostic Differentiation Between Two Rare Entities-Metastatic Peritoneal Mesothelioma With Duodenal Involvement and Duodenal Synovial Sarcoma: A Case Report.

This case report highlights the diagnostic challenges in distinguishing between metastatic peritoneal mesothelioma with duodenal involvement and synovial sarcoma of the duodenum, two rare and complex entities. A 59-year-old woman presented with nonspecific abdominal symptoms, and imaging revealed a heterogeneous lesion between the right hepatic lobe and duodenum. Endoscopic ultrasound-guided biopsy and subsequent histopathological analysis initially suggested synovial sarcoma, but further examination, including a FISH assay, confirmed the diagnosis of malignant peritoneal mesothelioma.