Appendiceal-origin pseudomyxoma peritonei masked by culture-positive neutrocytic ascites: a case report

Pseudomyxoma peritonei (PMP) is a rare peritoneal surface malignancy, most often of appendiceal origin. Diagnosis may be delayed when symptoms are indolent or when ascitic fluid studies suggest infection. A 65-year-old man presented with 1 year of progressive abdominal distension and 15 days of epigastric pain. He was haemodynamically stable and afebrile. Paracentesis showed cloudy exudative ascites with marked neutrophilia (17 900 cells/mm³; 52% neutrophils). Culture grew Escherichia coli and cytology was negative. Portal venous phase CT demonstrated complex hyperattenuating ascites, diffuse peritoneal implants with bulky omental caking, visceral scalloping and an abnormal enhancing appendix. Ultrasound-guided omental core biopsies confirmed high-grade mucinous carcinoma peritonei without signet-ring cells, supporting an appendiceal-type primary. The patient declined surgical exploration and died shortly after readmission with bowel perforation and abscess. This case underscores that characteristic CT findings should prompt tissue confirmation and explicit tumour grading even when ascites appears infectious.