History
The classic locations of anorectal abscesses, listed in order of decreasing frequency, are as follows:
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Perianal (60%)
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Ischiorectal (20%)
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Intersphincteric (5%)
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Supralevator (4%)
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Submucosal (1%)
The clinical presentation correlates with the anatomic location of the abscess (though it should be kept in mind that a perianal abscess sometimes is not an isolated superficial lesion but represents the point of a more involved perirectal abscess).
Almost all perirectal abscesses are associated with perirectal pain that is indolent in nature. Patients with a perianal abscess typically complain of dull perianal discomfort and pruritus. The pain often is exacerbated by movement and increased perineal pressure from sitting or defecation. Those with an ischiorectal abscess often present with systemic fevers, chills, and severe perirectal pain and fullness consistent with the more advanced nature of this process. External signs are minimal and may include erythema, induration, or fluctuance.
As many as 50% of patients with perirectal abscesses may present with swelling around the rectum, and as many as one quarter may present with rectal or perirectal drainage that may be bloody, purulent, or mucoid. [2, 4] These patients may also present with constipation, most likely due to pain on defecation, but the absence of constipation or even diarrhea does not rule out the diagnosis. Most of them report no history of fever or chills.
In many cases, these patients delay presentation to a physician, or they have already presented to a physician and have been given alternative diagnoses. [2, 4] Furthermore, complaints of abdominal pain are rare in these patients.
In addition to these symptoms, various case reports in the literature describe patients with perirectal abscesses who present with penile discharge, hip pain, or an ingested foreign body. [16, 17, 18]
Physical Examination
Patients with anorectal abscesses usually have normal vital signs on initial evaluation, with only 21% reporting fevers or chills. Physical examination demonstrates a small, erythematous, well-defined, fluctuant, subcutaneous mass near the anal orifice. On digital rectal examination (DRE), a fluctuant, indurated mass may be encountered. In one study, however, clinicians were unable to identify abscesses in 10% of patients on rectal examination; 4% of patients showed no signs of perirectal abscesses on initial examination. [2]
Optimal physical assessment of an ischiorectal abscess may require anesthesia to alleviate patient discomfort that would otherwise limit the extent of the examination. Patients with an intersphincteric abscess present with rectal pain and exhibit localized tenderness on DRE. Physical examination may fail to identify an intersphincteric abscess.
Although rare, supralevator abscesses present a similar diagnostic challenge. As a result, clinical suspicion of an intersphincteric or supralevator abscess may require confirmation by means of computed tomography (CT), magnetic resonance imaging (MRI), or anal ultrasonography (see Workup).
Digital examination with anesthesia can be helpful in certain cases, because patient discomfort can significantly limit physical assessment. For example, optimal evaluation for an ischiorectal abscess is performed in this manner. A fistula tract can be injected with peroxide solution at the time of examination under anesthesia in order to facilitate visualization of the internal opening of the fistula.
Complications
Complications of anorectal abscesses may include the following:
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Fistula formation
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Bacteremia and sepsis, including seeding of the infection to other areas by hematogenous spread
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Fecal incontinence
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Malignancy [19]
Fistulas occur in 30-60% of patients with anorectal abscesses. The intersphincteric glands lie between the internal and external anal sphincters and are associated most commonly with abscess formation. Fistulas arise through obstruction of anal crypts or glands and are identified by purulent drainage from the anal canal or from the surrounding perianal skin. Other potential causes of anorectal fistulas include diverticular disease, inflammatory bowel disease, [20] malignancy, and complicated infections (eg, tuberculosis or actinomycosis).
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Illustration of major types of anorectal abscesses (submucosal type not pictured).
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Goodsall rule for anorectal fistulas. Fistulas that exit in posterior half of rectum generally follow curved course toward posterior midline, whereas those that exit in anterior half of rectum usually follow radial course to dentate line.
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Goodsall rule for anorectal fistulas. Note curved nature of posterior fistulas and radial (straight) orientation of anterior fistulas.
