Anorectal Abscess – Drainage

Introduction

Anorectal abscess is a debilitating condition originating from a cryptoglandular infection in the anal canal in about 90% of patients, and it remains one of the more common anorectal conditions encountered in general surgical practice. In approximately 50% of patients, a fistula-in-ano subsequently develops, which usually requires surgical correction to prevent recurrent abscess and address symptoms. Without definitive closure of the fistula tract, patients experience persistent purulent drainage, intermittent perianal swelling and tenderness, followed by spontaneous discharge. In 1976, Parks and colleagues categorized fistulas based on their anatomical course relative to the sphincter complex ( Figure 33-1-1 ): intersphincteric, trans-sphincteric, suprasphincteric, and extrasphincteric.

Fistulas may also be classified as simple or complex . Simple fistulas include intersphincteric and low trans-sphincteric tracts. Complex fistulas encompass high trans-sphincteric fistulas, suprasphincteric and extrasphincteric fistulas, multitract fistulas, fistulas with blind extensions, horseshoe fistulas, and fistulas associated with inflammatory bowel disease, irradiation, or malignancy. Given the attenuated nature of the anterior sphincter complex in women, fistulas in this location may also be considered complex.

Several new surgical modalities have been introduced in recent years for the treatment of complex anorectal fistula: the anal fistula plug (AFP); the button plug, or Rectovaginal Plug (RVP; Cook Surgical, Bloomington, Ind.), and the ligation of the intersphincteric fistula tract (LIFT) procedure. This new generation of procedures emphasizes an important principle of sphincter-sparing techniques in anorectal fistula surgery and seeks to minimize injury to the anal sphincter mechanism. The principles of each of these new surgical modalities recognizes that fistula-in-ano is a simple hydrostatic system, wherein the primary opening is the high-pressure source of fluid passing through a conduit, the fistula, to the low-pressure opening, the secondary opening in the perianal skin. When these simple and logical engineering principles are applied to fistula surgery, new surgical modalities and devices evolve to treat fistula-in-ano without the disfiguring, painful, and morbid surgeries of the past. These new modalities are addressed in this chapter.

Anorectal Abscess

The vast majority of anorectal abscesses are cryptoglandular in origin; however, they may also result from Crohn's disease, trauma, or iatrogenic causes (e.g., proctectomy, ileal pouch). Regardless of the source, these abscesses are classified based on location into perianal , ischiorectal, intersphincteric , and supralevator (see Figure 33-1-1 ). In addition, abscesses originating in the deep postanal space may extend to the ischiorectal fossa unilaterally (hemihorseshoe) or bilaterally (horseshoe abscess). Depending on the location and size of the abscess, patients may complain of a variety of symptoms, ranging from local pain, tenderness, and a fluctuant mass (perianal and ischiorectal abscess) to normal external findings with deep-seated rectal pain (intersphincteric abscess) or even abdominal pain (supralevator abscess).

Initial Evaluation

The diagnosis of anorectal abscess is most often made based on the patient's history and physical examination. However, it is important to distinguish anorectal abscess from other perianal suppurative processes such as hidradenitis suppurativa , low pilonidal abscess, or infected sebaceous cyst. In addition, the presence of large “elephant ear” skin tags or multiple fistulas suggesting Crohn's disease should be noted because this may require a more detailed workup and conservative surgical approach.

Perianal and ischiorectal abscesses almost always present as a characteristic tender, fluctuant mass; patients with intersphincteric or supralevator abscesses may have a paucity of external findings, with only pelvic or rectal tenderness or fluctuance on digital rectal examination. Careful inspection may reveal other clues: a prior surgical drainage site or an old fistulotomy scar. Palpation of the perianal area and gentle digital rectal examination may reveal the subtle “fullness” of an intersphincteric abscess or the distinctive “boggy” feel of a supralevator abscess.

In the setting of an acute abscess, anoscopy and sigmoidoscopy should be deferred. Presence of cellulitis or fasciitis should be noted and should trigger a more aggressive surgical approach combined with antibiotic therapy. In general, laboratory evaluation adds little useful information but may be useful in patients with complex comorbidities such as diabetes, HIV, or other immunosuppressive diseases, where it can be used to monitor resolution of sepsis and confirm adequate systemic response to surgical drainage.

Imaging Studies

Although anorectal abscesses are most commonly diagnosed based on clinical findings, adjunctive radiologic studies can occasionally provide valuable information in certain situations. Pelvic computed tomography (CT) scan or magnetic resonance imaging can be helpful in identifying occult abscesses such as supralevator, deep postanal space, and deep ischiorectal or intersphincteric abscess. Another useful role for pelvic CT is in the morbidly obese; identifying deep anorectal abscess may be extremely difficult in this population, and pelvic CT can prove to be an invaluable aid to directing surgical drainage ( Figure 33-1-2 ).

Treatment

Fistula-in-Ano

There are two basic, important principles to be followed when treating patients with anal fistulas: First, it is important to accurately establish the relation of the fistula tract to the internal and external sphincter as defined in the Parks classification (see Figure 33-1-1 ). Second, it is important to accurately identify the location of the causative primary opening.

Physical examination under adequate anesthesia in the operating room is the best method for determining the course of a fistula. In addition to careful use of a fistula probe, injecting hydrogen peroxide into the external opening will help identify the internal opening in more than 80% of patients; Goodsall's rule helps predict the location of the internal opening by dividing the anal canal into anterior and posterior segments via an imaginary transverse line through the anal verge ( Figure 33-1-3 ). Fistulous tracts with external openings posterior to this line tend to generally follow a course to the posterior midline (12 o'clock position) crypt, such as horseshoe ( Figure 33-1-4 ) or hemihorseshoe fistulas ( Figure 33-1-5 ). Anterior fistulas tend to track in a radial fashion internally to the dentate line. The most common exception to Goodsall's rule is the horseshoe fistula (with primary opening at posterior midline) and long tracts that extend into the anterior quadrants of the anal canal. Other exceptions are iatrogenic fistula, Crohn's disease, and in women with anterior openings, in whom a higher percentage will track to the anterior midline.