Even though the drainage procedure may be performed in any position (depending on the overall setting in clinic, emergency room, or the operating room), the prone jackknife allows best access to all perirectal spaces including the deep postanal space.

The anus is again carefully examined with visual inspection, external palpation, and a (bi) digital examination. The perirectal and ischioanal tissue are gently palpated between the inserted index finger (inside the rectum) and the external thumb in order to define areas of thickening/induration, relation to sphincters, and (if patient awake) pain (Fig. 123.1A). “Fluctuance” is not a prerequisite for treatment as it may be absent even if an abscess is quite large.

After administration of adequate anesthesia (local or general), the area is disinfected with povidone-iodine solution (Betadine). Perform (at least) proctoscopy as part of the pre- or intraoperative evaluation to assess for obvious signs of malignancy or inflammatory bowel disease. The goal of the procedure is to create a sufficient size opening to allow drainage of pus and debris, and avoid premature skin closure. Make the opening as close as possible to the anal verge to ensure that the resulting fistula tract will be short (Fig. 123.1B). If the abscess location in uncertain, an 18-gauge needle on an aspirating syringe can be used before drainage to confirm the presence/location of pus. If electrocautery is available, excise a skin disk over the maximum of the abscess; alternatively, perform a cruciate incision and remove the edges. As soon as the abscess cavity is reached, pus should flow abundantly; otherwise the incision needs to be deepened with a clamp until the correct level is reached. In contrast to past recommendations, digital breakdown of loculations should be avoided if possible (particularly in absence of general anesthesia) as it has been associated with a higher incidence of incontinence.

Management of an underlying fistula is only of secondary priority: If the procedure is performed under general anesthesia, it may be reasonable to excise the cryptoglandular origin and place a seton (as outlined in the next section); however, the inflamed tissue carries an increased risk of creating false passages and is not well suited for flap procedures or the plug.

A horseshoe abscess involving the deep postanal space and both ischioanal fossae should be accessed through a radial incision in the posterior midline between coccyx and anal verge (modified Hanley procedure); two counter incisions in the anterolateral quadrants are made to place lateral Penrose drains that are secured by looping them.

Submucosal abscesses are drained into the rectum, rather than externally. For this purpose, an anal retractor is placed to expose the abscess. The location is confirmed by aspiration with a needle and syringe. Incise the mucosa overlying the abscess and allow it to drain into the rectum. If the cavity is large, place a Penrose drain or mushroom catheter into the abscess cavity to keep it open. Generally, such a drain will be passed within 1 to 2 days.

Antibiotics alone do not resolve a perirectal abscess and are not routinely needed; they may be given in support if there is a substantial phlegmonous component or if the patient is immunocompromised.

Specific locations around the anus are best described by assigning them to one of four quadrants (left/right, anterior/posterior). The alternative “clock-face” nomenclature is confusing if the patient’s position changes. Abscesses and fistulas are commonly classified according to the path taken by the burrowing infection relative to the external anal sphincter and the pelvic floor muscles (Fig. 123.1A,C).