The most likely causes of anal narrowing are anal diseases, such as rectal tumors, hemorrhoids, rectal polyps and rectal ulcers, etc., as follows: 1. The patient will not have other obvious discomfort; 4. Rectal ulcer: especially after the ulcer is malignant, the enlarged mass will lead to narrowing of the intestinal cavity and anus, which will be accompanied by loss of appetite, weight loss, anemia, increased frequency of bowel movement, and The symptoms may be accompanied by loss of appetite, weight loss, anemia, increased frequency of bowel movements and urgency.