From Ascites to Malignant Peritoneal Mesothelioma: The Diagnostic Workup of a Rare Tumor.

Background/Aim: Ascites is a common clinical manifestation of a wide spectrum of heterogeneous underlying conditions. All possible causes of ascites should be considered in the differential diagnosis to ensure an appropriate diagnostic workup. Among the rare causes, malignant peritoneal mesothelioma must be considered, as its diagnosis is particularly challenging. Case Report: We present the case of a 77-year-old female who developed ascites and lower-quadrant abdominal pain. She had no prior history of cancer and no documented occupational exposure to asbestos or other known carcinogens. After exclusion of the principal benign and malignant causes of ascites, we performed a biopsy and 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT). The final diagnosis was primary malignant peritoneal mesothelioma, an extremely rare tumor. Conclusion: This case highlights the complexity of the differential diagnosis. The diagnostic work-up for peritoneal mesothelioma must integrate the patient's clinical history, physical examination, tumor markers, and imaging findings. Biomarkers such as mesothelin and advanced imaging modalities including PET/CT assume an increasingly important role in staging and in distinguishing peritoneal disease entities.