Epithelial neoplasms and other epithelial lesions of the appendix (excluding carcinoid tumours)

Epithelial tumours of the appendix include low-grade mucosal-based tumours with an excellent prognosis as well as invasive carcinomas that are frequently fatal. Low-grade mucinous neoplasms spread to the peritoneum as pseudomyxoma peritonei, and the nomenclature of these tumours has been the subject of considerable disagreement among pathologists. Invasive adenocarcinomas are more often mucinous than colorectal carcinoma and may also spread to the peritoneum. These tumours also lack uniform terminology. In this article, the clinical and pathologic features of low-grade appendiceal mucinous tumours and appendiceal adenocarcinomas are reviewed. In addition, serrated polyps and serrated adenomas, whose significance in the colon is only beginning to be understood, are considered in the appendix. Retention cysts, hyperplastic polyps, and diffuse mucosal hyperplasia, although not truly neoplastic, are reviewed here as they may enter into the differential diagnosis of appendiceal mucinous neoplasms.