Cookies are used by this site. Occasionally Endo Anal Ultrasound EAU or Magnetic Resonance Imaging MRI are needed to determine the number and direction of fistula tracts, and to determine the amount of muscle sphincter involved prior to any planned surgery. Rarely fistulas are high, arising from above the anal canal supralevator fistula. This technique is known as anal sac expression. Investigation The diagnosis is made clinically, and confirmed by an Examination Under Anaesthesia EUA , where a probe is gently inserted into the fistula tract to confirm a communication between the outside perianal skin and the internal lining of the anal canal. In surgical usage, however, the rectum is frequently taken to include the upper part of the anal canal, as far down as the pectinate line see fig. Opossums use their anal glands when they " play possum ".
Surgery may be needed if medicine fails to heal a tear (fissure) in the anus. The preferred procedure is an internal anal sphincterotomy. A doctor makes a small. Internal Anal Sphincter. The internal anal sphincter is an extension of the circular muscle layer of the colon and rectum (Fig. 1A). The sphincter is a ring of smooth. anal sphincter (sphincter a´ni) either of two sphincters (the internal and external anal sphincters) that open and close to control evacuation of feces from the anus.