The causes of perianal swelling are the following three: First, if the patient has had hemorrhoids in the past, a large amount of stimulating food in the diet such as a large amount of alcohol can lead to swelling of the hemorrhoid nucleus and congestion of the hemorrhoid veins, thus causing pathological hypertrophy and downward movement of the anal cushion around the anus, thus forming. Second, if the patient often diarrhea, easily lead to anal gland infection, the infection later spread along the anal canal to the perianal area thus will form perianal abscess, in the early performance of an inflammatory mass, in the late may form pus, fluctuation is obvious, generally positive, the perianal ultrasound can be a clear diagnosis. Third, if the patient has a history of striking or squatting, it will also manifest as perianal swelling, local redness, swelling, heat and pain.