Dysplastic intestinal-type metaplasia of appendiceal endometriosis: a mimic of low grade appendiceal mucinous neoplasm

Abstract

We report an example of dysplastic intestinal-type metaplasia involving endometriosis of the appendix in a 45 year old woman. One other example of this phenomenon has been reported. As it occurs within the muscular wall of the appendix, confusion with low grade appendiceal mucinous neoplasm (LAMN) may occur. Evidence supporting the metaplastic nature of the intestinal epithelium is offered. As the initial pathological diagnosis was of invasive cancer with perforation of the appendix treatment consisted of peritonectomy and hyperthermic intraperitoneal chemotherapy (HIPEC).

Virtual slides: The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1068246472111756.

Figure 1

Histologic findings. a) Low power view of rupture site with free mucin and a dysplastic intestinal-type gland (arrow). b) Low power view of normal appendix epithelium with underlying endometriosis. c) Low power view of endometriosis of the appendix wall with transition to intestinal-type epithelium (arrows). (d and e) Further low power views of endometriosis of the appendix wall with transition to intestinal-type epithelium. f) Higher power view of 1e. Note intestinal-type epithelium (arrow). g) High power view of endometriosis, intestinal-type metaplasia, and intestinal-type metaplasia with low-grade atypia (arrows left to right). h) High power view of an area of tufting in low grade dysplasia.

Figure 2

Immunohistochemical findings. a) Cytokeratin 7 positivity limited to endometriotic epithelium. b) Cytokeratin 20 positivity limited to intestinal-type epithelium. c) CD10 positivity of endometriotic stroma on which both endometriotic and intestinal-type epithelilia rest. d) CD10 positive endometriotic stroma surrounding intestinal-type glands. (e and f) ER positivity of endometriotic epithelium and stroma, but absence in metaplastic epithelium. g) Rare ER positive “transitional” cells with intestinal-type differentiation (arrows).