A perianal abscess may be drained with local anesthesia. A cruciate or elliptical incision is made over the point of maximal tenderness and the edges trimmed to prevent premature closing (which could lead to recurrence). No packing is required.

Most ischioanal abscesses can be drained similarly to a perianal abscess, but the location of the incision should be shifted medial toward the anal side of the abscess but lateral to the external sphincter muscle (this minimizes the complexity if a fistula develops). Large abscesses or horseshoe abscesses (with the infection usually originating from the deep postanal space) often require drainage with regional or general anesthesia in the prone or left lateral position.

For a horseshoe abscess, a midline incision between the anus and coccyx is made and the superficial external sphincter muscle fibers are spread to enter the deep postanal space. Counter-incisions are made over each ischioanal fossa to allow drainage of the anterior extensions (Hanley procedure). The distal half of the internal sphincter may be divided to drain the gland where the infection originated (Fig. 13.3).

For pain out of proportion to physical findings, an exam under anesthesia is mandatory. An intersphincteric abscess may be established by palpation of a mass or aspiration of pus in the operating room. The treatment is division of the internal anal sphincter along the length of the abscess. The wound may be marsupialized for adequate drainage.

A supralevator abscess may result from an upward extension of an intersphincteric or ischioanal abscess or downward extension of a pelvic abscess. If the origin is from an intersphincteric abscess, drainage is accomplished through the rectum by dividing the internal sphincter (not through the ischioanal fossa as that would result in a suprasphincteric fistula). If the origin is an ischioanal abscess, this is drained through the perianal skin (not through the rectum as that would lead to an extrasphincteric fistula) (Fig. 13.4). If the abscess is of pelvic origin, it can be drained via the area it is pointing: through the rectum, ischioanal fossa, or percutaneously via the abdominal wall.

The area of maximal tenderness is prepped and the skin around it is infiltrated with local anesthesia (injecting at the maximal point of fluctuation may preclude the local anesthesia working in that acid environment).

A stab incision is made as close to the external sphincter muscle as possible so the tract is as short as possible in case a fistula develops.

A 10–16 French soft mushroom catheter is inserted over a probe into the cavity. It typically does not need to be sutured in place.

The catheter is shortened to 2–3 cm outside the skin with the tip in the depth of the abscess (Fig. 13.5a, b).

The length of time that the catheter is left to drain the abscess cavity depends on the size of the abscess cavity, amount of granulation tissue around the catheter, and character and amount of drainage. If in doubt, it is better to leave it longer.

Primary fistulotomy at the time of abscess drainage is controversial.

A meta-analysis showed that when the fistula is identified, drainage plus primary fistulotomy decreased the rate of subsequent fistula formation (by 83 %) with no increase in incontinence.

Against primary fistulotomy:

Those younger than 40 years old have a significantly higher risk of developing a fistula or recurrent abscess after initial drainage of a perianal abscess.

Abscess recurrence is more often observed after drainage of an ischioanal abscess.

If the internal opening of a low transsphincteric fistula is readily apparent at the time of abscess drainage, primary fistulotomy is feasible EXCEPT in patients with Crohn’s disease, acquired immune deficiency syndrome (AIDS), advanced age, high transsphincteric fistula, and an anterior fistula (in women).

Antibiotics are only used as an adjunct for patients with valvular heart disease, prosthetic heart valves, extensive soft tissue cellulitis, prosthetic devices, diabetes, immunosuppression, or systemic sepsis.

Early recognition, aggressive surgical debridement, and appropriate antibiotic administration are the most important factors to improve outcome and reduce mortality.

Vigorous resuscitation with invasive monitoring and respiratory and renal support is aggressively carried out (and treated).

Antibiotics effective against Staphylococci, Streptococci, gram-negative coliforms, Pseudomonas, Bacteroides, and Clostridium are administered intravenously. If a gram stain shows gram-positive rods, penicillin G (24–30 million units per day) and an aminoglycoside are given.