The classification, pathology, treatment, and prognosis of pseudomyxoma peritonei (PP) are not fully settled and are still being debated. Several studies published in the literature have suggested subdivision of PP into a low-grade type (termed Diffuse Peritoneal Adenomucinosis) and a high-grade type (termed Peritoneal Mucinous Carcinomatosis (PMCA) (Ref: Ronnett et al; Am J Surg Pathol 19:1390-1408, 1995). The image shown here is a section from one of the mucin globules in a case of pseudomyxoma peritonei. It contains pools of extracellular mucin associated with fibrosis and scant strips of simple mucinous epithelium lacking cytologic atypia. It meets the criteria for DPAM. The primary appendiceal tumor in most cases of DPAM is a mucinous cystadenoma. In cases of PMCA, the primary tumor is usually an appendiceal or colonic mucinous adenocarcinoma. The mucin in such cases contains more abundant proliferative epithelium with marked cytologic atypia and increased mitotic activity.