has been reported to be as high as 47%.13

In patients who are at high risk of experiencing postoperative incontinence, an alternative approach

may be the use of an advancement flap. This procedure involves excision of the fissure, surrounding scar

tissue, and any skin tags. A variety of flap configurations including V-Y, Y-V, house, and others have

been employed to help close the defect. Healing rates following fissurectomy and advancement flap are

comparable to those following sphincterotomy.

Anorectal Abscess

The vast majority of anorectal abscesses result from infection of the glands that empty into the anal

crypts within the anal canal at the level of the dentate line. Other causes of anorectal abscess include

inflammatory bowel disease, trauma including iatrogenic (usually gynecologic or surgical) trauma,

infections such as tuberculosis and actinomycosis, and malignancy. Since these glands lie within the

intersphincteric space, blockage of a duct results first in an intersphincteric abscess which can then

spread to the surrounding spaces (Fig. 70-16). The most commonly encountered anorectal abscess occurs

in the perianal area, followed in frequency by ischioanal, intersphincteric, and supralevator (Fig. 70-17).

Figure 70-16. Pathways of infection start in the intersphincteric space (A) and then spread to perianal spaces, forming perianal

abscesses (B).

Figure 70-17. Classification of anorectal abscess.

Clinical Manifestations

Most patients with anal abscess present with pain. In patients with perianal or ischioanal abscesses, pain

may be accompanied by swelling and erythema. Conversely, patients with supralevator abscess are less

likely to present with swelling and may have accompanying fever. Patients with severe rectal pain may

also develop urinary retention.

Management

Treatment of anorectal abscesses requires incision and drainage; antibiotics alone are ineffective and

may allow the suppurative process to progress to a more complicated abscess. The use of antibiotics in

conjunction with drainage may be considered in the patient with concomitant cellulitis or in

immunocompromised patients.

Most patients with perianal abscesses can be treated in an outpatient setting under local anesthesia.

An elliptical or cruciate incision is made over the most tender area or area of fluctuance, and the skin

edges are trimmed to prevent early closure of the wound, and all loculations are drained. Routine

culture of the drainage is not recommended. Packing is also not necessary; rather, patients are

instructed to soak the area in warm water and simply keep the wound covered with gauze.

Patients with superficial ischioanal abscesses may be treated in a similar fashion, however patients

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with deeper or more complex abscesses typically require an examination under anesthesia with drainage

in the operating room. Less commonly, patients may present with bilateral ischioanal abscess, a

condition referred to as a horseshoe abscess. These infections typically begin in the deep postanal space,

which spread to both ischioanal areas. Treatment requires that the deep postanal space be drained,

which is accomplished by making a longitudinal incision in the skin between the tip of the coccyx and

the anus and exposing the anococcygeal ligament. The ligament is then divided and the deep postanal

space drained; counter incisions are then made overlying the ischioanal areas as well.

Patients with intersphincteric abscess often present with severe anorectal pain, however no indurated

or fluctuant area is evident. These patients also typically require an examination under anesthesia. In

the operating room, an intersphincteric abscess can be diagnosed by palpation of a protrusion into the

anal canal or aspiration of purulent fluid from the intersphincteric space. Drainage is performed by

dividing a portion of the internal sphincter muscle along the length of the abscess cavity.

Supralevator abscesses are less common and can often be difficult to diagnose. Because the location of

the abscess is adjacent to the abdominal cavity, patients may present with abdominal or pelvic pain.

Digital examination may demonstrate induration or a tender mass located in the distal rectum above the

level of the anorectal ring. The etiology of a supralevator abscess dictates its management. These

abscesses may result as an extension of an intersphincteric abscess, extension of an ischioanal abscess, or

may result from an intra-abdominal abscess from perforated diverticulitis, appendicitis, or Crohn’s

disease. Supralevator abscess secondary to extension from an ischioanal abscess should be drained

through the ischioanal area. Supralevator abscess secondary to extension from an intersphincteric

abscess should be drained into the rectum, as drainage through the ischioanal area may result in a

complex suprasphincteric fistula. Percutaneous drainage may be an option in patients with supralevator

abscess secondary to an intra-abdominal source.

Rarely, anorectal abscess can result in necrotizing infection and death, a condition referred to as

Fournier gangrene. This situation may result from a delay in diagnosis and management of an anorectal

abscess, infection with a highly virulent organism, or may be due to patient factors such as diabetes or

compromised immune function. The infection superficially spreads around the perineum, causing

necrosis of the skin and underlying muscle and fascia. Treatment includes empiric broad-spectrum

intravenous antibiotics and prompt surgical debridement of the necrotic tissue until healthy tissue is

encountered.

Anal Fistula

6 A fistula is generally defined as an abnormal communication between two epithelialized surfaces. Anal

fistula (or fistula-in-ano) represents a communication between the anorectal canal and the perianal skin

as the result from spontaneous or surgical drainage of an anorectal abscess. The incidence of fistulas

following abscess drainage ranges from 5% to 83% in the medical literature, but is generally thought to

occur in one-quarter to one-third of patients.14 Anal fistulas may also occur in up to 30% of patients

with Crohn’s disease.

Classification

Treatment of anal fistulas is in part dictated by the type of fistula. Fistulas are classified by their

relation to the anal sphincter complex (Fig. 70-18).15 The most common type is the intersphincteric

fistula, followed by transsphincteric, suprasphincteric, and extrasphincteric (Box 70-1).

Clinical Manifestations

The majority of patients with anal fistula have a history of previous anorectal abscess which either

spontaneously drained or were surgically incised. Recurrence of anorectal abscess in the same location

often indicates the presence of an underlying fistula. Patients complain of drainage, intermittent

swelling, pain with defecation, and occasional bleeding. Physical examination often demonstrates an

external opening on the perianal skin with granulation tissue. Drainage of fecal, purulent, or

serosanguinous drainage may be evident or can be elicited with digital rectal examination or

compression of the fistula tract.

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Figure 70-18. The four main anatomic types of fistula.

Box 70-1 Classification of Anal Fistulas

Intersphincteric Fistula. The tract of the fistula lies within the intersphincteric space and the external

opening lies close to the anal verge. These fistulas are the most common, and typically result following

a perianal abscess.

Transsphincteric Fistula. The fistula tract begins in the intersphincteric space and then traverses

through a portion of the external sphincter muscle. The external opening typically lies over the

ischioanal fossa.

Suprasphincteric Fistula. The fistula tract begins in the intersphincteric space and then passes upward

above the external sphincter and then perforates the levator ani muscles to drain through the ischioanal

fossa.

Extrasphincteric Fistula. The fistula tract begins in the distal rectum rather than the anal canal and

perforates the levator ani muscles to drain through the ischioanal fossa. These fistulas are rare and

develop typically from Crohn’s disease or rectal trauma.

Hidradenitis suppurativa may present in a similar fashion to anal fistula, with multiple openings on

the perianal skin with surrounding induration. Unlike anal fistulas, however, any tracks associated with

hidradenitis are superficial and do not communicate with the anal canal. A pilonidal sinus with perianal

extension may also mimic an anal fistula, but in this situation the tract moves superiorly, away from the

anal canal. Much less commonly actinomycosis can mimic a complex fistula.

Examination under anesthesia is recommended in order to treat any undrained abscess and to identify

the internal opening. Flexible sigmoidoscopy may also be performed to evaluate for concomitant

inflammatory bowel disease or malignancy. Under anoscopic guidance, a fistula probe can be inserted

into the external opening through the fistula tract to determine the location of the internal opening.

Goodsall rule states that if an imaginary line is drawn transversely across the anus, an external fistula

opening seen posterior to this line will originate from an internal opening in the posterior midline,

whereas an opening anterior to this line will originate from the closest anal crypt (Fig. 70-19).

Locating the internal opening is not always possible with a fistula probe, and in this situation other

diagnostic maneuvers may be necessary. Injection of the external opening with hydrogen peroxide

either with or without the use of endoanal ultrasound may help identify smaller fistulas. For patients

with multiple or complex fistulas, fistulography with a water soluble contrast and fluoroscopy has been

described, although the use of magnetic resonance imaging has largely replaced this.

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