Pseudomyxoma peritonei with negative ascitic cytology: a rare case report

Background: Pseudomyxoma peritonei (PMP) is a very rare, indolent cancer characterized by the accumulation of mucinous ascites in the peritoneal cavity and is commonly caused by a low-grade appendiceal mucinous neoplasm. Case: We report a case of a 66-year-old man who presented with a 4–5-month history of progressive abdominal distension and abdominal pain. Investigations showed a cystic lesion associated with the appendix on computed tomography (CT) scan, hemorrhagic, gelatinous (jelly-like) ascites on drainage, significantly elevated tumor markers (carcinoembryonic antigen and cancer antigen 19-9), and hypermetabolic peritoneal and omental thickening without distant metastases or an isolated fluorodeoxyglucose (FDG)-avid focal mass on FDG-positron emission tomography/computed tomography. Colonoscopy findings were normal, and ascitic fluid cytology was negative for malignancy. Peritoneal biopsy during diagnostic laparoscopy showed high-grade mucinous carcinoma peritonei [Peritoneal Surface Oncology Group International (PSOGI) classification], of presumed appendiceal origin. The patient was subsequently lost to follow-up. Discussion: The present case demonstrates that negative ascitic cytology does not exclude PMP and that histopathological examination of a peritoneal biopsy is essential when clinical and radiological suspicion remains high. Conclusion: Negative ascitic cytology does not exclude PMP. In progressive mucinous ascites with typical imaging and tumor-marker findings, early peritoneal biopsy and multidisciplinary referral are advised. However, because the patient was lost to follow-up, no conclusions can be drawn regarding treatment response or survival.