Peritoneal Carcinomatosis Revealed by Ascitic Fluid Cytology

Background: Ascitic fluid cytology is a rapid diagnostic tool for malignancy, yet its sensitivity can be variable and often depends on sample volume and ancillary techniques. Case presentation: We report a case of an elderly patient presenting with progressive abdominal distension and hemorrhagic ascites. Biochemical analysis showed exudative features (total protein 38 g/L; LDH 700 U/L). Cytological examination of fresh and methylene-blue-stained preparations revealed clusters of atypical cells with nuclear pleomorphism suggestive of malignancy. Infectious causes were excluded (sterile bacteriology). Thoraco-abdominopelvic CT confirmed diffuse peritoneal carcinomatosis, and histopathology of peritoneal nodules revealed infiltrating tubulo-papillary carcinoma of gastrointestinal origin. Discussion: Ascitic cytology is highly specific for detecting malignancy, particularly peritoneal carcinomatosis, where sensitivity may approach 96–97% when adequately performed. However, sensitivity is more modest in general, ranging from approximately 56–75%, and can be improved with larger sample volumes (≥ 80 mL up to 200 mL). In this case, recognition of cytologically malignant cells allowed expedited diagnosis and directed imaging and histological confirmation, underscoring the importance of sufficient sample volume and integration with imaging and pathology for timely management. Conclusion: This case highlights the diagnostic utility of ascitic fluid cytology in suspected malignant ascites and emphasizes the role of adequate sampling and adjunctive pathological techniques to enhance detection accuracy.