Intestinal metaplasia and colonization of endometriosis in a case of an appendiceal mucinous neoplasm

Abstract

Intestinal endometriosis is reported in 15–37 % of patients with pelvic endometriosis [1]. Making a correct diagnosis can be challenging for clinicians as well as for pathologists as this disease is able to mimic other pathologies such as inflammatory bowel disease, infectious etiologies, or neoplasms. The appendix is less commonly involved than the small or large intestine. Endometriosis of the appendix is often asymptomatic and discovered as an incidental finding, but it may also present as an acute or chronic appendicitis, occasionally with the formation of an inflammatory mass, mimicking a neoplasm [1]. A few case reports describe the development of obstructive mucocoeles secondary to endometriosis of the appendix. These mucin-filled cystic dilatations of the appendix were lined by normal epithelium without hyperplastic or neoplastic changes [2]. We report the case of an appendiceal mucinous neoplasm in association with endometriosis in a 48-yearold woman. The appendiceal lesion was an incidental finding in this patient who underwent imaging for an episode of pancreatitis. Surgery was performed. Microscopic examination demonstrated that the cystic lesion was covered by a mucosa with serrated and dilated crypts that assumed Land inverted T-shapes (Fig. 1). The crypts were lined by columnar epithelial cells with low-grade atypia. With the presence of extra-appendiceal acellular mucin, this lead to the diagnosis of a low-grade mucinous neoplasm with low risk of recurrence [3]. In addition, the wall of the appendix showed numerous foci of endometriosis consisting of endometrial glands embedded in variable amounts of endometrial stroma, confirmed with ER and CD10 immunohistochemistry (not shown). Interestingly, some of the glandular structures that were embedded in the endometrial stroma were lined by mucinous epithelium, very similar to the epithelium observed in the appendiceal mucinous neoplasm. Immunohistochemistry demonstrated CK7 expression in the normal endometrial epithelium and CK20 expression in the mucinous epithelium. Two theories could explain this finding. Firstly, the epithelium of the appendiceal mucinous neoplasm colonizes the endometrial glands of the appendiceal endometriosis. In intestinal endometriosis, endometrial glands can merge with the surface epithelium and be continuous with it [1, 4]. Secondly, the endometrial glands undergo metaplastic mucinous changes. Mucinous metaplasia in endometriosis is a well-known phenomenon, although it more often mimics endocervical epithelium. Intestinal-type mucinous metaplasia with goblet cells and Paneth cells has been described, but is rare [5]. In our opinion, both explanations can account for the observations in this case. In a few glands, both types of epithelium were continuous. The transition between the normal endometrial epithelium and the mucinous epithelium was very abrupt. Focally, some Paneth cells were present. The glands were dilated and showed serrated growth pattern. Similar cytological and architectural characteristics as recognized in the neoplasm and the sharp demarcation between both types of epithelium suggest that the mucinous changes of the epithelium are due to colonization of the endometrial glands (Figs. 2, 3, 4, and 5). In other areas, the L. Libbrecht :K. Geboes : C. Cuvelier : L. Ferdinande (*) Department of Pathology, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium e-mail: Liesbeth.Ferdinande@UGent.be