Approach

The goal of treatment of anorectal abscesses is to achieve adequate drainage of the abscess without damaging the anal sphincters.[4]

Antibiotics are not an alternative to surgical drainage of these abscesses. Guidelines recommend reserving adjunctive antibiotics for patients with associated cellulitis, immunocompromise, or signs of systemic infection.[4] Antibiotic therapy is also indicated for patients with diabetes and cardiac valvular disease. In these circumstances, a broad-spectrum antibiotic with anaerobic and gram-negative coverage would be appropriate. 

Drainage of the abscess should be accomplished without undue delay because of the potential for the abscess to spread into a necrotizing, soft-tissue infection leading to life-threatening sepsis.[11][23] The development of a necrotizing, soft-tissue infection is more common in older adults, patients with diabetes, and immunosuppressed individuals (e.g., patients with HIV, alcoholism, or malignancy; those receiving chemotherapy; those with history of solid organ transplant), and has been reported to have a mortality between 25% and 35%.[24] However, some evidence suggests that immunosuppressed patients with neutropenia and lack of fluctuance on examination may be treated initially with antibiotics alone, with surgical drainage considered after multi-disciplinary consultation.[4][25]

External drainage of perianal and perirectal abscess is appropriate, while intersphincteric and supralevator abscesses should be drained internally into the anal canal and rectum, respectively, to avoid the creation of extrasphincteric or suprasphincteric fistulas. For patients with anorectal abscesses associated with Crohn disease, treatment of the underlying condition should be considered after the acute anorectal sepsis has been treated.[1][26] See Crohn disease (Management approach).

The management of an anal fistula is controversial.[27][28][29][30][31]

Surgical management

Perianal abscesses can frequently be drained in the office or emergency department using local anesthesia and drained externally using an incision that is oriented in a radial fashion relative to the anus. This incision has the potential to damage the anal sphincters if the incision is extended too far medially, but in those patients who have an associated anal fistula, it will make subsequent fistula management simpler. Perirectal abscesses should be drained in the operating room where optimal anesthesia can be achieved.

An alternative for drainage of the abscess is a curvilinear incision that is parallel to the anus. This incision has a decreased risk to the anal sphincters, but can make subsequent management more challenging for those patients with an associated anal fistula. Whichever incision is used, either an ellipse of skin can be removed, or a second, smaller incision can be made perpendicular to the primary incision at its midpoint (cruciate incision) to prevent reapproximation of the skin edges. A small drainage catheter can be used to facilitate drainage of deeper infections.

If examination at the time of surgical drainage reveals an associated anal fistula, consideration can be given to managing the fistula at the same time.[4][28][30][31] A Cochrane review has suggested that fistula surgery should be carried out at the time of abscess drainage, as this reduces the persistence and recurrence of the abscess/fistula and the need for further surgery, and that the intervention should be recommended in carefully selected patients.[32] Anal fistulae that are superficial, involving less than 30% of the sphincter mechanism, can be managed by fistulotomy.[4] An alternative would be the placement of a loose, plastic seton to act as a drain.[27][29] The seton will reduce the risk of recurrent anorectal abscess and will allow for sphincter-preserving management of the fistula after the acute infection has resolved and the fistula tract has matured. If the anal fistula is found to involve more than 30% of the sphincter mechanism, fistulotomy is not an option but consideration can still be given to placement of a seton to prevent recurrent anorectal abscess.[23]

If the abscess is being drained outside the operating room or under local anesthesia, it may not be possible to perform an adequate anal examination or place a seton. In this circumstance, there is a risk of recurrent anorectal abscess. Intersphincteric and supralevator abscesses frequently require general anesthesia to allow for an adequate anal examination to make a diagnosis and drain the abscess. These abscesses should be drained internally into the anal canal and rectum, respectively.[10][16] Anal fistulas only rarely occur after drainage of these abscesses so there is no need to consider fistula management at the time of abscess drainage.

Postoperative wound care

Postoperatively, patients should begin comfortably warm water baths 2 or 3 times daily to clean the wound until complete healing has occurred. Baths should also be used for cleansing after bowel movements. Absorbent dressings can be used to prevent staining of the underclothes if drainage continues. There is no good quality evidence to support the use of internal dressing (packing) for healing perianal abscess cavities.[33]

Adjunctive antibiotic therapy

Usually reserved for patients with associated cellulitis, immunocompromise, or signs of systemic infection.[4] Antibiotics are also indicated for patients with diabetes or a history of cardiac valvular disease. Broad-spectrum antibiotics with anaerobic and gram-negative coverage should be started preoperatively and be discontinued within 24 hours of surgery or after cellulitis has resolved. There is no standardized antibiotic regime in the literature. In general, some combination of an intravenous broad-spectrum penicillin (e.g., ampicillin/sulbactam) or a second- or third-generation cephalosporin (e.g., cefoxitin or cefotetan) is combined with either clindamycin, ciprofloxacin, or metronidazole.

There is no clinical evidence to support triple antibiotic coverage. While some authors also recommend adding an aminoglycoside (gentamicin or tobramycin) to the regimen, potential complications should be considered. Aminoglycosides are known to cause nephro- and ototoxicity. If used for more than 24 hours, serum levels need to be monitored.

For patients who present with a necrotizing soft-tissue infection, broad-spectrum antibiotics as described above are mandatory. In addition, a more aggressive surgical approach is warranted with complete debridement of infected soft tissues. Multiple trips to the operating room are frequently needed before the necrotizing process is brought under control. Given the lethality of necrotizing soft-tissue infections, care in an intensive care unit is necessary.[24]

Treatment failure

Adequate drainage of the abscess should result in a prompt improvement in the symptoms. If not, re-examination under anesthesia is indicated to ensure complete drainage of the abscess. Inadequate drainage of the abscess occurs most commonly in patients with horseshoe abscesses when the postanal or ischiorectal component of the abscess is more prominent and is drained, but the other components of this abscess are not recognized and treated.[34][35]

Recurrence of the anorectal abscess will occur in about 11% of patients, usually from an unrecognized anal fistula.[27][36] For patients who develop a recurrent anorectal abscess or whose wound from the initial drainage fails to heal, examination by a general or colorectal surgeon is indicated to exclude an anal fistula as the cause of these problems. For patients with recurrent anorectal abscess and risk factors such as HIV or immunosuppression, or patients from a developing region, consideration may also be given to some of the rare causes of anorectal abscess such as tuberculosis or actinomycosis. Specific microbiologic and culture techniques may be needed to identify these conditions.[20][21]

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