When it comes to anorectal stenosis (thinning and shrinking of the anorectum, difficulty in defecation, thinning of the stool, which some people describe as “cat shit”), I believe that every patient who has to undergo anorectal surgery is very worried about it, or even have palpitations when they think about it. So why does it cause anorectal stenosis? Normally, the maximum diameter of the anal canal during defecation is 75 px, and the sigmoid colon is about 62.5 px where it joins the rectum. the maximum diameter in the rectum can be 5-175 px. from a professional point of view, it is normal for the index finger to pass through the anorectum without anesthesia. When it is difficult to pass the index finger or the little finger cannot pass it either, there is definitely a stricture. It is believed that congenital malformation, inflammatory stimulation, external injury, tumor, and spasm are the main factors causing stenosis. 1. Congenital malformation: It is the most important stenosis factor in childhood. These children usually have normal sphincters, but even if the “atresia” is surgically cut, there is still a possibility of stenosis. 2, chronic inflammatory stimulation: recurrent chronic anal fistula, especially complex anal fistula, fistula walking between the sphincter, or rectal submucosal fistula, due to chronic inflammatory stimulation, fibrous tissue hyperplasia, scar contracture to the anal canal or rectal stenosis. In addition, ulcerative proctitis, catarrhal proctitis, and granulomatous proctitis often cause rectal stricture. Dysentery, lymphogranuloma schistosomiasis infection, tuberculosis and gonorrhea can also cause rectal stenosis. 3, various injury factors: such as anal trauma, burns, radioactive injury, corrosive drug injury, etc. can cause anorectal stenosis. In particular, the medical source of injury occupies a large proportion in the clinic, such as mixed hemorrhoids with external peeling and internal ligation, which damage the skin and mucous membrane; external hemorrhoids with epithelial defects; internal hemorrhoids or rectal submucosal injection of more sclerosing agents, which produce a sterile inflammatory reaction and local fibrin coagulation, resulting in scarred anorectal stenosis after the formation of scar tissue; after rectal mucosal circumcision; and after colorectal anastomosis, which can cause anorectal stenosis. rectal stenosis. 4, tumor factors: including benign tumors and malignant tumors. For example, tumors occurring in the intestinal epithelium (rectal adenoma, adenocarcinoma, etc.) often cause intestinal stenosis due to tumor growth or infiltration. Tumors occurring in the intestinal wall such as smooth muscle tumors or smooth muscle sarcomas can lead to rectal stricture. In addition, vaginal and uterine tumors, prostate cancer, lymphoma, presacral cysts, and sacrococcygeal teratoma can cause anal stricture. In addition, patients who have suffered from anal fissures for a long time, repeated ulcer stimulation can lead to spasm of the internal anal sphincter and loss of retardation, and over time, fibrotic hyperplasia can form on the surface of the internal anal sphincter thus leading to the occurrence of anal stricture. The exact type of stenosis can only be determined after examination.