Ultrasound of the anus is a common diagnostic aid that can clarify the nature of the lesion, which can be substantial, such as an inflammatory mass, or fluid, such as an abscess. Ultrasound of the anus is usually divided into ultrasound of the perianal surface, which should be kept clean, and then the patient should be placed in a suitable position, such as lying on his or her side, and then the ultrasound probe should be used to spread around the anus to observe whether there are abnormal echoes, and if found, the location, size and shape of the lesion should be recorded in detail. Anal ultrasound sometimes includes endorectal ultrasound, which can clarify the location, extent, and nature of deep perianal abscesses and fistula lesions. An endoluminal ultrasound probe is applied and the rectum should be emptied first to keep it clean, then the ultrasound probe is placed in the rectum, a suitable position is chosen, and then the lesion is observed.