Perianal Abscess: Definition, Classification, Symptoms, Causes, Diagnosis and Treatment

Men are twice as likely as women to have anal abscesses, which are most common between the ages of 20 to 60.

Perianal and perirectal abscesses are common anorectal problems .

The infection most often originates in a blocked anal crypt gland, with the resulting pus accumulating in the subcutaneous tissue, the intersphincteric plane, or beyond (ischiorectal space or supralevator space) where various types of anorectal abscess form.

A fistula is the chronic manifestation of an anorectal abscess. The most common etiology of an anorectal fistula is an infected anal crypt gland.

Classification of abscesses

Ischiorectal abscesses (ischioanal abscesses)

These penetrate through the external anal sphincter into the ischiorectal space.

Intersphincteric abscesses

Only 2% to 5% of all anorectal abscesses are located in the intersphincteric sulcus between the internal and external sphincters.

As a result, they often do not cause changes in the perianal skin, but can be palpated during digital rectal examination as a fluctuating mass that protrudes into the lumen.

Supralevator abscess

They can originate from two different sources: the typical cryptoglandular infection that travels superiorly within the intersphincteric plane to the supralevator space, or an inflammatory pelvic process caused by Crohn’s disease or perforated colon by diverticular disease or cancer.

The potential source of pelvic infection is best determined from the patient’s history.

Horseshoe abscess

They are complex perirectal abscesses that most often form posterior to the anal canal.

The potential space where the abscess originates is joined by the pelvic floor at the top, by the anococcygeal ligament at the bottom, and by the coccyx and anal canal.

Due to these relatively rigid boundaries, abscesses in this space are forced to spread into the ischiorectal space, either unilaterally or bilaterally (horseshoe).

Symptoms of perianal abscesses

Patients with an abscess often have severe pain in the anal or rectal area.

The pain is constant and is not necessarily associated with a bowel movement.

Symptoms of an anal abscess include:

  • Anal pain, particularly during bowel movements, but also while sitting and active, swelling and redness around the anus.
  • Symptoms like fever and malaise are common.
  • Patients may also experience smelly, intermittent perianal drainage, if the abscess has started to drain spontaneously. Itching may be observed.
  • Bleeding from the anus
  • Constipation,
  • Pain when urinating

Causes of anal abscess

The risk of having an anal abscess is higher if you have:

  • Diabetes.
  • Inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis , or another long-term (chronic) bowel condition.
  • Anal sex.
  • A weakened immune system, whether from illness, malnutrition, or drug abuse.
  • Having previously had an anal abscess (up to 50% of abscesses recur) or an anal fistula (perianal abscess fistula).

About one in two people with an anal abscess develops an anal fistula, a tunnel between the anus and the rectum.


On physical examination, an area of ​​fluctuation or a patch of indurated, erythematous skin may be seen overlying the perianal skin in patients with a superficial (perianal) abscess.

If the abscess is deeper they may not have physical signs on external examination, and the abscess can only be felt by digital rectal exam or imaging.

The perianal skin can become excoriated and inflamed. The external opening may be visualized or palpated as an induration just under the skin if the external opening is incomplete or blind.

The external opening may be inflamed, tender, and / or draining purulent fluid. A palpable cord may be present running from the external opening to the anal canal.

The internal opening in the anus can be seen by an anoscopic exam, while a sigmoidoscope may be required to view the internal opening in the rectum. In some cases, the internal opening can be felt on a digital rectal exam.

An anorectal abscess should be suspected in patients who present with severe pain in the anal or rectal area.

A superficial anorectal abscess can be diagnosed on physical examination with findings of perianal erythema and a palpable, often fluctuating mass.

A deeper abscess can be diagnosed by feeling a tender, often fluctuating mass internally on digital rectal examination or by imaging studies.

Imaging studies, such as computed tomography, MRI, and transperitoneal or endorectal ultrasound, can confirm the diagnosis when a deep anorectal abscess is suspected, but cannot be palpated by external examination or digital rectal examination.


Once diagnosed, all perianal and perirectal abscesses should be drained immediately, the lack of fluctuation should not be a reason to delay treatment.

Any undrained anorectal abscess may continue to expand into adjacent spaces, as well as progress to generalized systemic infection.

A perianal abscess must be drained through an incision in the skin. The procedure can be carried out in an outpatient setting, such as the office / clinic, the emergency department, or the procedure room.

However, perirectal abscesses are more complex and must be drained in the operating room, preferably under local or general anesthesia.

Smaller perirectal abscesses may be amenable to drainage under local anesthesia with intravenous sedation.

Surgical approaches vary depending on the site of the abscess.