Pathologic diagnosis, origin, and natural history of pseudomyxoma peritonei.

Mucinous ascites and pools of mucin within the peritoneal cavity associated with neoplastic, mucinous epithelium are the characteristic features of pseudomyxoma peritonei (PMP). Clinically, PMP presents with abdominal distension and gelatinous ascites. In female patients, pelvic masses can be seen. Radiologic findings on computed tomography include scalloping of the hepatic and splenic margins and dense ascites. Surgically, PMP is encountered as grossly visible mucin in the peritoneal cavity. The presence of mucin outside of the appendix, in the right lower quadrant, and beyond is an important diagnostic finding. The appendix may be distended or ruptured. In women, there is often bilateral surface involvement of the ovaries, raising the differential diagnosis of primary ovarian neoplasms; however, these are extremely rare causes of PMP. Because of the association between appendiceal lesions and metastatic mucinous neoplasms of the ovary, appendectomy in the setting of any mucinous peritoneal or ovarian process may be prudent, even if the appendix is grossly normal. The gastrointestinal tract, especially the hepatopancreato biliary system, also needs to be assessed by the surgeon. Pathologically, PMP arises almost exclusively from low- or high-grade mucinous neoplasms of the appendix. These neoplasms must be distinguished both from rare benign causes of mucinous ascites and from nonappendiceal primary tumors. PMP has a protracted clinical course with progressive fibrous adhesions and obstructive disease; aggressive surgical and cytoreductive therapy with hyperthermic intraperitoneal chemotherapy has been reported to improve clinical outcomes.