Colorectal endometriosis - a challenging, often overlooked cause of colorectal pathology: a clinicopathological review of 114 cases.

The colon is the most common site for endometriosis outside the genital tract. It has a varied presentation and can mimic numerous other conditions, both clinically and pathologically. We investigated the clinicopathological features of a series of colorectal endometriosis with a particular emphasis on the features seen in cases with colonic mucosal involvement. A total of 114 consecutive cases of colorectal endometriosis were reviewed. Forty-eight percent did not have a prior diagnosis of endometriosis and in 34 patients (30%) the endometriosis was determined as the cause for the presentation. Mucosal involvement was present in 31 specimens. Features of chronic colitis were seen in the adjacent mucosa in 90% of cases whilst there were glandular changes mimicking adenocarcinoma in two cases (1.8%). Fifty percent of cases with mucosal involvement also showed glands with a hybrid intestinal-endometrial phenotype by morphology and/or by immunohistochemistry. Endometriosis is an important mimic of other conditions.