Histopathologic study of the rectum in 1,438 consecutive rectal specimens in a single Japanese hospital: I. benign lesions

The author investigated histopathology of 1,438 consecutive rectal specimens in the last 10 years of our pathology laboratory in Japan. A computer review of pathologic reports was done. Observations of pathologic slides were performed, when appropriate. The rectal specimens were composed of 1,022 benign lesions and 416 malignant lesions. The 1,022 benign lesions were composed non-specific proctitis (n=460, 45%), adenoma (n=248, 24%), ulcerative colitis (n=98, 10%), hyperplastic polyp (n=54, 5%), carcinoma in adenoma (n=40, 4%), rectal ulcer (n=37, 4%), serrated adenoma (n=24, 2%), hyperplastic nodule (n=21, 2%), Crohn's disease (n=9, 1%), ischemic proctitis (n=8, 0.8%), mucosal prolapse syndrome (n=7, 0.6%), juvenile polyp (n=6, 0.6%), lymphoid hyperplasia (n=5, 0.5%), lipoma (n=4, 0.4%) and amebic dysentery (n=2, 0.2%), and mature cystic teratoma (n=1, 0.1%). In this article, histopathological features of these benign lesions were described in details. In particular, adenomas were classified into adenomas with mild, moderate, and severe atypia, serrated adenoma, and carcinoma in adenoma. The later are mainly seen in large adenoma with severe atypia. Ulcerative colitis was characterized by continuous lesion, crypt abscess, abnormal branching, and deletion of goblet cells. Crohn's disease was characterized by transmural inflammation and epithelioid granulomas. Ischemic colitis was characterized by ischemic necrotic changes and pseudomembrane formation. Mucosal prolapse syndrome was characterized by abnormal muscle in the mucosa (fibromuscular obliterance). Juvenile polyp was characterized by abnormal dilations of the crypts. Lymphoid hyperplasia must be differentiated from MALT lymphoma. Lipoma was ordinary lipoma without lipoblasts. Amebic dysentery was characterized by ulcer and presence of histiocyte-like entamoeba histolitica. Mature cystic teratoma was characterized by hairs and other elements of skin and mesodermal and endodermal components.