Jump to content. An anal fissure is a tear in the lining of the lower rectum anal canal that causes pain during bowel movements. Anal fissures don't lead to more serious problems. Most anal fissures heal with home treatment after a few days or weeks. These are called short-term acute anal fissures.
An anal sphincter is a group of muscles at the end of the rectum that surrounds the anus and controls the release of stool, thereby maintaining continence. There are two sphincter muscles: one is internal and one is external. The external muscle helps maintain continence and keep stool in the rectum. If there is a loss of muscle control in the sphincter, incontinence may occur. The inner muscle is not under voluntary control but rather is controlled by the autonomic nervous system.
Ultrasound scans use high frequency sound waves to create a picture of a part of the body. You might have one to find out the size of a cancer and whether it has spread. The ultrasound scanner has a microphone that gives off sound waves. The microphone links to a computer that turns the sound waves into a picture.