Pathophysiology

The cryptoglandular hypothesis states that an infection
begins in the anal gland and progresses into the muscular
wall of the anal sphincters to cause an anorectal abscess.
Following surgical or spontaneous drainage in the perianal
skin, occasionally a granulation tissue–lined tract is left
behind, causing recurrent symptoms. Multiple series have
shown that the formation of a fistula tract following
anorectal abscess occurs in 7-40% of cases.

Physical examination findings remain the mainstay of
diagnosis. The examiner should observe the entire
perineum, looking for an external opening that appears as
an open sinus or elevation of granulation tissue.
Spontaneous discharge via the external opening may be
apparent or expressible upon digital rectal examination.