Answer: Endometriosis

Histology: Sections show portion of colon with multiple foci of dilated benign glandular structures with associated cellular stroma in submucosa, muscularis propria and subserosal soft tissue. A single pericolic lymph node with a small ciliated epithelial lined dilated cyst without stroma is also noted.

Discussion: Endometriosis of the large intestine is rare and can present with symptoms of colonic malignancy including rectal bleeding, change in bowel habits, abdominal pain and rarely bowel obstruction. Clinical studies may show bowel stricture with evidence of bleeding with a differential diagnosis that includes diverticular disease and adenocarcinoma of the colon. Histologically, the diagnosis can be easily made by identifying endometrial type glands with associated cellular stroma/hemosiderin deposition. Endometriosis can be seen anywhere within the abdominal cavity with varying frequency and rarely outside of it, as well. Endometriosis/endosalpingiosis of lymph nodes has also been described.