Types of perirectal abscesses

One discussion this week involved perirectal abscesses.

Reference: Calandrella C, La Gamma N. Abscess, Perirectal. In StatPearls [NCBI Bookshelf]. Last updated: 2018 Oct 27.

Summary: Although often thought of as the same, perianal abscess and perirectal abscesses differ in both complexity and care options. Except for perianal abscess which can be simply incised and drained as definitive care, all others usually require intravenous antibiotics, surgical evaluation, and drainage. A majority of abscesses are diagnosed clinically based on skin findings and palpitation of the affected area alone, but some require advanced imaging to determine the extent of infiltration.

A perirectal abscess can be further divided into a category based on anatomical location: ischiorectal abscess, intersphincteric abscess, and supralevator abscess. Given the variability in location and severity of the abscess, it is important to consider the presence of fistulas or tracts which may contribute to the spread of the infection. Perianal abscesses are the most common type, followed by ischiorectal, and intersphincteric abscesses.

Alternatively, the Park’s classification system which groups the fistulas into 4 types based on the course of the fistula and the relationship to the anal sphincters.

  • Intersphincteric (70%): Between the internal and external sphincters
  • Trans-sphincteric (25%): Extends thru the external sphincter into the ischiorectal fossa
  • Suprasphincteric (5%): Lasses from the rectum to the skin through the levator ani
  • Extrasphincteric (1%): Extends from the intersphincteric plane through the puborectalis

EPIDEMIOLOGY: The incidence of anorectal abscesses is 1:10,000, resulting in approximately 68,000 to 96,000 cases in the United States per year with a male prevalence of 3:1 during the third and fourth decades of life. The condition is seen more in the summer and spring months. Although often a concern of the patient, data does not support that there is an increased risk from hygiene, anal-receptive intercourse, diabetes, obesity, race, or altered bowel habits.

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