MUC5AC and pseudomyxoma peritonei: Histologically, a villous or flat proliferation of mucinous epithelium with low-grade atypia was a hallmark of the LAMNs with common mucin production in examination.5 10 Even though the LAMNs without definitive malignant features pursue a predictable clinical course in general, the precursor lesions to pseudomyxoma peritonei cannot be ruled out.1 Because prominent mucin production increases intraluminal pressure, which may penetrate into or through the appendix wall, subsequently disseminate to the peritoneal cavity, and cause mucinous ascites ultimately.