Colonoscopy is a relatively common method of adjunctive examination in clinical practice. Colonoscopy can clarify lesions in the small intestine, colon and rectum, such as the presence of polyps, ulcers, inflammation and bleeding. Colonoscopy has a strong auxiliary effect on the identification of intestinal lesions, but its effect on anal lesions is not particularly obvious. Because colonoscopy can only see the intestinal mucosa and submucosa, but perianal lesions, such as abscesses and perianal warts, cannot be identified through colonoscopy, for example, perianal abscesses, the depth and scope of which can be clarified by perianal ultrasound. Therefore, if an anal lesion occurs, it is usually not possible to perform colonoscopy, but to clarify its cause through perianal ultrasound or perianal MRI.