Anal distension often manifests itself as a sensation of anal cramping and increased frequency of bowel movements. The causes of anal distension are often anal diseases. First, internal hemorrhoids, inflammation and edema or embedded. Because of dry stool or other reasons, the internal hemorrhoid surface mucous membrane erosion edema, congestion, as well as a large number of thrombus formation under the mucous membrane, and in serious cases can be prolapsed outside the anus. And due to the spasm of the anal sphincter, resulting in venous reflux obstruction, further aggravating the edema, so that the nucleus of the hemorrhoid is embedded outside the anus. Second, anal sinusitis, anal sinusitis is the most common cause of anal swelling and painful fall. In addition, the anal sinus and anal flap inflammation is also called anal saphenous inflammation, which can further develop into perianal abscess. The third, proctitis, if the chronic colitis involves the rectum, can appear anal cramps and increased frequency of defecation, generally a long course of disease, recurrent episodes, the degree of severity of the disease varies. Fourth, rectal mucosal prolapse, also known as prolapse. As the name implies, the tissue inside the anus comes off outside the anus, and the anorectal mucosa comes out and accumulates in the rectum.