A fistula is an abnormal connection between two hollow spaces (technically, two epithelialized surfaces), such as blood vessels, intestines, or other hollow organs. Fistulas are usually caused by injury or surgery, but they can also result from an infection or inflammation.Fistulas are generally a disease condition, but they may be surgically created for therapeutic reasons.
In botany, the term is most common in its adjectival forms, where it is used in binomial names to refer to species that are distinguished by hollow or tubular structures. Monarda fistulosa, for example, has tubular flowers;Eutrochium fistulosum has a tubular stem; and Allium fistulosum has hollow or tubular leaves.
Types:Depending on their relationship with the internal and external sphincter muscles, fistulae are classified into five types:
Extrasphincteric fistulae begin at the rectum or sigmoid colon and proceed downward, through the levator ani muscle and open into the skin surrounding the anus. Note that this type does not arise from the dentate line (where the anal glands are located). Causes of this type could be from a rectal, pelvic or supralevator origin, usually secondary to Crohn’s disease or an inflammatory process such as appendiceal or diverticular abscesses.
Suprasphincteric fistulae begin between the internal and external sphincter muscles, extend above and cross the puborectalis muscle, proceed downward between the puborectalis and levator ani muscles, and open an inch or more away from the anus.
Transphincteric fistulae begin between the internal and external sphincter muscles or behind the anus, cross the external sphincter muscle and open an inch or more away from the anus.These may take a ‘U’ shape and form multiple external openings. This is sometimes termed a ‘horseshoe fistula’.
Intersphincteric fistulae begin between the internal and external sphincter muscles, pass through the internal sphincter muscle, and open very close to the anus.
Submucosal fistulae pass superficially beneath the submucosa and do not cross either sphincter muscle.