Rectal polyps have a variety of causes, and their development may be related to the following factors.

1. Abnormal tissue structure, such as juvenile polyps, that is, the misgrowth of polyps.

2. Genetic inheritance, such as familial adenomatous polyposis, is autosomal dominant. Patients often have a family history of the disease.

3. Infection part of the polyp can be infected by bacteria, parasites and other infections of the rectal mucosa, by the intestinal inflammatory lesions proliferation and polyps. Such as intestinal tuberculosis, intestinal schistosomiasis, ulcerative colitis.

(II) pathogenesis

1. Classification pathologically often divided into 2 categories of polyps: tumor polyps and non-tumor polyps.

2. Pathology

(1) Tubular adenomas: the most common, most of them are single, with tips, diameter is usually less than 1cm, in the intestinal mucosa surface bulge such as rice grains or soybean size, the surface is smooth or fine particles, the color is close to the normal mucosa, the texture is soft; large adenomas such as cherries or strawberries, with shallow grooves on the surface or lobular, the color is dark red, and seldom cancerous. Microscopic morphology may have different degree of change, the mild case is mild glandular increase, the epithelial cells have no abnormality, the severe case is not only obvious glandular hyperplasia, the morphology and staining of the epithelial cells are atypical changes, the nuclear division is increased, the further development of glandular cell pleomorphism, mesenchymal infiltration, which is regarded as the severe atypical hyperplasia or carcinoma.

(2) Chorionic adenoma: also known as papillary adenoma, it is chorionic and cauliflower-like protruding on the surface of the mucosa, and the scope of the lesion is limited to the mucous membrane layer; the tumor is soft in texture, broad-based and without clitoris, and its volume is larger than that of tubular adenomas; microscopically, the chorionic outgrowths are in branching form, forming an elongated papillomatous corolla mass (Figure 5). It is most common in the elderly, more in males than females, about 90% occur in the rectum and lower sigmoid colon, and are easily carcinomatous.

(3) Juvenile polyp: also known as congenital polyp, belongs to the misshapen polyp, mainly occurs in the children under 10 years old, 70% ~ 80% occurred in the rectum, most of them are single, less than 1cm, there is a tendency to disappear naturally after puberty.

(4) Inflammatory polyps (pseudopolyps): occur in the regeneration and repair stage of colorectal inflammatory diseases, mostly seen in ulcerative colitis, Crohn's disease, intestinal tuberculosis, schistosomiasis and so on. Often multiple, non-tibial, small size, rarely more than 5mm in diameter, is its characteristic, the color is lighter. Some of them may also have tips, and may increase in size to several centimeters when the disease is prolonged. Microscopically, the glands are elongated with intraluminal reflexes, resulting in a serrated appearance. Increased nuclear schizogenic activity is seen only at the basal level, and the epithelial cells have inconspicuous basally located nuclei, abundant cytoplasm, and are filled with mucus. The basement membrane beneath the surface epithelium is thickened and the surface epithelium has a micropapillary appearance. Hyperplastic polyps (chemotaxis polyps), mostly occurring in the rectum, mostly develop after 40 years of age, with age, the incidence increases.

(5) Familial adenomatous polyposis: It is an autosomal dominant disease, in which the colon is covered with polypoid adenomas of varying sizes, with or without tips, with a high tendency to become cancerous, occurring mostly after the age of 12.