A generally accepted explanation for the etiology of anorectal abscess and fistula-in-ano is that the abscess results from obstruction of an anal gland and the fistula is due to chronic infection and epithelialization of the abscess drainage tract. Anorectal abscesses are defined by the anatomic space in which they develop and are more common in the perianal and ischiorectal spaces and less common in the intersphincteric, supralevator,and submucosal locations.

“The diagnosis of anorectal abscess is usually based on the patient’s history and physical examination. Perianal pain and swelling are common with superficial abscesses, whereas drainage and fever occur less often. Deeper abscesses, such as those that form in the supralevator or high ischiorectal space, may also present with pain that is referred to the perineum, low back, or buttocks.”

Vogel JD, et al Clinical Practice Guideline for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula. Dis Colon Rectum. 2016 Dec;59(12):1117-1133 Free Full Text