The presence of abundant mucoid or gelatinous, cellular or acellular material in the pelvis and abdominal cavity (pseudomyxoma peritonei) that is associated with the presence of an ovarian mucinous cystic tumor. In the vast majority of cases, the presence of pseudomyxoma peritonei is the result of metastasis from a primary appendiceal or gastrointestinal tumor site, and the ovarian mucinous tumor is metastatic rather than primary. [from
NCI]