If internal rectal bleeding occurs, the person should be evaluated with a colonoscopy to determine the cause of the bleeding. Sometimes it is impossible to tell if the rectal bleeding is internal or external and further testing such as colonoscopy must be done. We have already described the small crypts, or little glands, in the lining of the anal canal which secrete oil. The high pressure from straining forces the stool into the crypts. Feces trapped in these little crypts can fester and cause infections, abscesses and fistulas.
Abscesses are pockets of pus within the flesh.
Abscesses can cause fistulas. Fistulas are tunnels through the flesh from the anal canal to the skin. Fistulas can cause chronic discharge or drainage. The abscesses are extremely painful, swollen and tender. Abscesses should be treated as soon as possible so that they do not damage the anal sphincter muscles.