Pseudomyxoma peritonei and selected other aspects of the spread of appendiceal neoplasms.

The varied aspects of spread of appendiceal neoplasms are reviewed with emphasis on the often clinically dramatic phenomenon known as pseudomyxoma peritonei, a term mostly used to describe grossly evident mucin within the peritoneal cavity. The majority of cases of pseudomyxoma peritonei result from tumors primary in the appendix, which are usually low-grade. On microscopic examination pseudomyxoma peritonei is typically characterized by large aggregates of mucin which may be relatively acellular or cellular containing strips of mucinous epithelium, mucinous epithelium encircling glands and cysts, or aggregates of mucinous epithelium lying within mucin pools. High-grade adenocarcinoma of the appendix may spread to the omentum and peritoneal surfaces without grossly striking mucin deposition and resemble spread of other high-grade gastrointestinal adenocarcinomas. In many cases of pseudomyxoma peritonei in females there is involvement of one, or more often, both ovaries. The size of the ovarian neoplasms characteristically dwarfs the often relatively unremarkable appearing appendix in these cases. The ovaries are typically multilocular, although one locule may dominate, and in cases in which the primary is a low-grade appendiceal mucinous neoplasm often have a "jelly-like" consistency. In cases of spread of frank adenocarcinomas the ovarian metastases typically have a more solid, albeit still somewhat gelatinous consistency. Microscopic examination of the ovaries typically shows surface involvement, a characteristic of spread to the ovaries in general, and the glands and cysts that replace most or all of the parenchyma are typically lined by tall mucin-rich cells with, in many cases, relatively bland microscopic features. In cases of frank adenocarcinoma, the tumors may mimic closely a primary mucinous adenocarcinoma of the ovary. Spread to the ovaries may also be seen in cases of frank intestinal-type adenocarcinoma primary in the appendix and the uncommon signet ring cell carcinoma of the appendix, the latter being one cause of the Krukenberg tumor. Occasional cases are reported in the literature of ovarian spread of goblet cell carcinoid tumor of the appendix, but in our opinion most of the primary tumors in those cases are better classified as adenocarcinomas, usually dominantly of signet-ring cell type, albeit sometimes with focal neuroendocrine differentiation. Other interesting aspects of spread of appendiceal neoplasms include to the lining of the uterus and the fallopian tube. In yet other cases the tumors may present clinically as incidentally discovered mucinous aggregates within hernia sac specimens or as a scrotal mass.