Specific Abscesses

Superficial anorectal abscesses are drained directly; the incision should be large enough to provide adequate drainage. Incisions should be made radially to avoid disruption of sensory and motor nerves.

Ischiorectal abscesses are deeper but they are approached in a manner similar to superficial abscesses. Whenever possible, these procedures should be done with the patient under anesthesia to allow for appropriate exposure and pain control. We routinely position the patient in the prone jackknife position, with buttock retraction using tape (Fig. 27-2, B). This position allows for optimal exposure for both surgeon and assistant. The incision should be large enough to allow for adequate drainage. Blunt dissection should be avoided to minimize damage to small nerves and blood vessels in the ischiorectal fossa. Packing of the abscess cavities is unnecessary and counterproductive to effective drainage and should be used only when needed to control hemorrhage.

The patient with intersphincteric abscess often shows no external stigmata of abscess. The patient will complain of severe pain, especially during defecation, and bedside examination is often prohibitively painful. In these cases, once the abscess is localized by needle aspiration, drainage through the wall of the rectum is indicated, with adequate division of the overlying internal sphincter musculature to allow for adequate drainage.

Supralevator abscesses should not be drained by the transanal approach and may require percutaneous drainage using interventional radiology, or appropriate operative control through a transrectal approach.

Abscess with Fistula

Often, perianal infection is accompanied by perianal fistula, and a careful survey must be done at surgery for any fistula. Purulent drainage through an internal fistula opening can sometimes be seen perioperatively, and if not, injection of dilute hydrogen peroxide or methylene blue through the abscess cavity can be performed to help elucidate fistulous anatomy. If no fistula can be easily found, simple abscess drainage is performed. If a fistula is encountered, it should be managed appropriately (see later section).

Deep Postanal Space

The deep postanal space abscess is a unique case that requires a high index of suspicion to identify. Chronic recurrent bilateral ischiorectal abscesses are called “horseshoe” abscesses and are pathognomonic for an abscess source in the deep postanal space. The deep postanal space is located cephalad to the anococcygeal ligament in the posterior midline and continues to bilateral ischiorectal spaces. Injection of either ischiorectal abscess cavity will usually result in drainage from an internal fistula in the posterior midline.

Effective management of these fistulas requires not only drainage through counterincisions over each ischiorectal space, but also unroofing of the deep postanal space. This approach requires division of the anococcygeal ligament and entry into this space (Fig. 27-3, A). The surgeon should work toward and just distal to the coccyx to guide the appropriate dissection. Division of the anococcygeal ligament and discharge of purulent fluid will confirm entry into this space.

If a fistula is encountered in the posterior midline, division of the internal sphincter musculature distal to the fistula and into the deep postanal space is performed to allow adequate drainage. Counterincisions over the ischiorectal abscess are performed, and drainage catheters or Penrose drains are passed through to facilitate decompression. In patients with recurrent fistula, wide division of the residual external sphincter may be required, termed the modified Hanley procedure.

Occasionally, deep ischiorectal fossa abscesses cannot be easily drained by superficial incisions. In these cases, drainage may be facilitated by placement of catheter with a mushroom or flared tip. This approach allows for continued drainage and development of a persistent tract, which will remain open after the catheter is removed (Fig. 27-3, B).

Types of Fistula

Fistulas are defined by their anatomic relationship to the pelvic floor musculature and sphincter complex (Fig. 27-4, A). The majority of fistulas track low through the subcutaneous soft tissue with minimal sphincteric involvement and are termed simple, or superficial. Simple lay-open fistulotomy is a time-honored and effective approach with a high success rate. Complex fistulas traverse a significant component of the sphincter or levator musculature and must be approached with caution. Performing a fistulotomy would require division of significant amount of sphincter muscle and may impair the continence mechanism.

Intersphincteric fistulas track through the intersphincteric space and exit on the perianal skin. Transsphincteric fistulas traverse both internal and external sphincter muscles. Extrasphincteric fistulas track above the sphincter complex from an internal opening and exit superficially, whereas suprasphincteric fistulas originate above the muscular pelvic diaphragm and exit externally.

The relationship of the external opening to the anal verge can offer clues as to the source of the internal opening using Goodsall’s rule: An imaginary line is drawn transversely across the anal opening, and fistulas anterior to this line generally track radially to internal rectal openings (Fig. 27-4, B). Fistulas posterior to this line, as well as those located greater than 2 cm from the verge, tend to originate from a posterior midline opening.