Non-carcinoid epithelial tumours of the appendix--a proposed classification.

Examination of 33 cases of non-carcinoid epithelial tumours of the appendix and a review of the previous literature has led us to propose a new classification of these lesions. It is based on nomenclature currently used for similar mucosal proliferations in the colon, facilitating communication between pathologists and clinicians with respect to their nature and possible behaviour. The use of the term "mucocele" to describe any lesion in which there is mucinous distension of the appendiceal lumen, irrespective of the type of underlying mucosal pathology, is now largely discredited. Yet, although a resemblance of some appendiceal lesions to similar lesions in the colon has been recognized, current terminology is still confused by the use of "cystadenoma". We have been able to place all of the known non-carcinoid appendiceal mucosal tumours into 4 main diagnostic categories, these being--adenoma, hyperplasia, mixed adenoma/hyperplasia and adenocarcinoma, and propose these terms as the basis for a new classification.