Anorectal Abscess and Fistula

Localized infection with a collection of pus in the anorectal area is designated an anorectal abscess. Usually, it results from the invasion of the normal rectal flora into the perirectal or perianal tissues. The pathologic process seems to start with inflammation of one or more of the crypts (see Chapter 104 ), spreads to the anal ducts and anal glands, and then spreads submucosally, subcutaneously, or transsphincterally to the surrounding tissue. This sequence of events closes with the spontaneous rupture of the abscess, either into the anorectal canal or through the perianal skin, if the abscess has not been drained surgically. After the abscess has perforated, the cavity and its outlet shrink, leaving a tubelike structure, an anorectal fistula, which invariably is the result of the abscess. Therefore, the abscess is the acute phase, and the fistula is the chronic phase.

The levator ani plane, demarcating the various perineal pelvic spaces, is used to classify anorectal abscesses according to localization. Retrorectal, pelvirectal, and submucosal abscesses belong to the supralevator abscesses and have a somatic sensory nerve supply; therefore, these cause a sensation of discomfort from pressure rather than from pain in the anorectal region. Infralevator abscesses may produce signs of toxemia and prostration. Retrorectal and pelvirectal abscesses originate from infectious processes in other pelvic organs and thus are not anorectal lesions in the strict sense, although they usually rupture into the rectum or the anal canal. Infralevator abscesses are also divided according to site into subcutaneous, intramuscular, fistulorectal, and cutaneous abscesses. The fistula is called complete when both openings, the primary and the secondary, can be detected and are accessible. Such a complete variety usually connects the rectal lumen with the anal or perianal skin. If there is only one opening, it is called a blind fistula or a sinus.

Fig. 105.1 depicts the various types of fistulas (or fistulae) and the Goodsall-Salmon law, in which an imaginary transverse line across the center of the anus can be used to predict the location of the tract and the primary opening.

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Anorectal Abscesses and Fistulae.

Anorectal abscess and fistula are associated with specific diseases, such as Crohn disease, malignancy, radiation proctitis, leukemia, lymphoma, tuberculosis, actinomycosis, and lymphogranuloma venereum. Other diseases may cause a similar picture, such as diverticulitis and Bartholin abscesses.