Development of Dysplastic Mucinous Epithelium from Endometriosis of the Appendix

Aim: We report an unusual case of mucinous metaplasia and epithelial dysplasia occurring in endometriotic epithelium in the appendix.

Methods And Results: A 39-year-old woman developed an appendiceal endometriosis in which the endometrial glands displayed extensive areas consisting of mucinous epithelium and Paneth cells. Focally the mucinous epithelium showed low-grade epithelial dysplasia. These changes occurred in portions of the endometriotic tissue closest to the appendiceal lumen. Both the intestinal and endometrial epithelial components were surrounded by typical endometrial-type stroma showing positive reactivity for oestrogen receptor.

Conclusions: Formation of the mucinous epithelium most likely represents a metaplastic process of the endometrial epithelium rather than a result of a simple 'collision' of the appendiceal and endometrial epithelium. Further support for this being a metaplastic process was the presence of glandular structures containing a mixture of mucinous cells, goblet cells, Paneth cells, ciliated and nonciliated endometrial cells, and ciliated and nonciliated mucinous cells, all showing the same positive reactivity for oestrogen receptor. The disposition of mucinous epithelium in the foci of endometriosis in this case suggests that the appendiceal mucosa or extracellular mucin may play a role as an inducer of mucinous cell metaplasia in endometriotic epithelium.