CHAPTER 107 Perianal Abscess Incision and Drainage
A perianal abscess is one of the most painful anal conditions seen in the outpatient setting. The pain of a perianal abscess is severe, disabling, and progressive, and the only relief these patients obtain is with spontaneous rupture of the abscess or when they seek medical attention for incision and drainage (I&D). The most common etiology of perianal abscess is thought to be an infection originating at the dentate line in the anal crypts (see Chapter 97, Clinical Anorectal Anatomy and Digital Examination). The infection then usually migrates through the path of least resistance to the perianal tissues, where there is a closed-space environment ideal for proliferation of this mixed bacterial infection.
The four locations where abscesses can occur and their relative incidence are shown in Figure 107-1. The most common site of an abscess in the anal area is in the perianal tissues immediately adjacent to the anal verge (60%). If the abscess is located 2 to 3 cm away from the anal verge, then it is most likely in the ischiorectal location (25%), just outside the anal sphincters. An intersphincteric abscess occurs in the intersphincteric plane, between the internal and external sphincters. An abscess in this location may not be externally visible or palpable in the perianal tissues. The pain of an abscess is present but the diagnosis will be confirmed only on digital anorectal examination, where the fluctuant mass is easily palpable. The least common abscess in this area is in the supralevator location, and is more correctly identified as a perirectal abscess as opposed to a perianal abscess. Most clinicians would agree that if a supralevator abscess is diagnosed, they must look for an intra-abdominal or pelvic source. A supralevator abscess may be associated with appendicitis, diverticulitis, pelvic inflammatory disease, or other pelvic or abdominal disease.
