Anorectal Abscess

Introduction to Anorectal Abscesses

Figure X | Image courtesy of Science Photo Library Opens in new window

Anorectal abscess is an infection that begins in the anal glands and extends into spaces around the anus and rectum. Twice as many males have this condition as females.

Epidemiology

Anorectal abscesses may occur in association with a variety of medical illnesses and are two to three times more common in men than in women. In most cases no specific etiological cause can be found, but specific factors may include inflammatory bowel disease Opens in new window, infection, trauma, surgery, malignancy, radiation and immunosuppression.

Clinically they tend to present with perianal pain, swelling, and sometimes fever. Examination reveals a tender, erythematous and fluctuant mass. Complex and recurrent anorectal abscesses may be well delineated by intrarectal ultrasound. One classification is according to the four potential anorectal spaces they may occupy (see Figure X1).

Figure X1 | Classification of anorectal abscesses

Patients at Risk

Anorectal abscesses are more common in patients with a variety of chronic medical conditions compared to the general population.

Patients at risk include those with Crohn’s disease Opens in new window, diabetes, heart disease, lymphoma, leukemia, anal and rectal cancer, radiation proctopathy, hidradenitis suppurativa Opens in new window, and infections of the perianal region. Anorectal abscesses can be caused by a variety of infections including, Chlamydia infection, actinomycosis, and tuberculosis.

Pathophysiology

By definition, an anorectal abscess is a collection of pus in the perianal or perirectal region (see Figure X). The process is most likely initiated by obstruction of the anal glands followed by infections with the above-mentioned organisms or colonic bacteria.

Infection may then expand into a variety of spaces within the anorectal region. The four most important locations where pus may accumulate are the perianal, ischiorectal, intersphincteric, and supralevator spaces (see Figure X1).

1. Perianal Abscess

Perianal abscess presents as a painful lump around the anal verge, usually lateral and posterior to the anus. It may result from an infected anal gland or, more rarely, is a presentation of Crohn’s disease. Systemic symptoms are uncommon. On examination most will be poinint, with an indurated red area which may be fluctuant.

Such abscesses can be drained under local anesthesia, with the assistance of sedation or inhalation analgesia. Incision should be stab-like, circumferential to the anal ring, but long enough to allow complete evacuation of pus.

2. Ischiorectal Abscess

Ischiorectal abscesses usually tend to be larger, yet may present with less dramatic cutaneous findings because of the compressibility of ischiorectal fat.

Patients may be febrile and look toxic, with systemic symptoms. The area of induration is likely to be large and more lateral than a simple perianal abscesses. Pointing may not occur until late, and may seem more like buttock cellulitis. Treatment should be exploration and drainage under general anesthesia, usually with proctosigmoidoscopy and possibly biopsy at the same time.

3. Supralevator Abscess

This abscess arises from above the levator ani. In reality, it’s a pelvic abscess and is often secondary to an intra-abdominal condition such as diverticular disease or Crohn’s disease. Fever is common, and it may present as a pyrexia of unknown origin. The patient may present with pain on defecation and altered bowel habit. Inspection of the perineum may be normal, but rectal examination will reveal a firm, spongy, tender mass. Treatment is exploration and drainage under general anesthesia by a surgeon with colorectal experience.

4. Intersphincteric or Submucous Abscess

These abscesses may be associated with severe pain and with urinary symptoms. They are within the anal canal, so no external swelling may be visible. They point within the anal canal and may rupture spontaneously. Treatment is exploration and drainage under general anesthesia by a surgeon with colorectal experience.

Symptoms

The most common symptoms are pain and swelling in the anorectal region. Anal discharge and anorectal bleeding may be present.

Diagnosis

The diagnosis is made by taking appropriate history and physical examination. Examination reveals a swollen, tender, erythematous, warm enlargement in the perianal region. Some drainage may be present and a pin-like opening may be revealed. Anesthesia may be required to complete the examnation, including a digital rectal evaluation.

Treatment

The treatment of all anorectal abscesses is incision and drainage. Depending on local practice, some small superficial abscesses may be able to be treated in the emergency department (ED) if anesthesia to achieve adequate drainage can be achieved.

Larger and more complicated abscesses are best treated under general anesthesia by a surgeon with colorectal experience. The drained wound should be kept open long enough for the abscess to heal from below. This can be achieved by excising an ellipse of skin, or a cruciate incision with the skin edges excised or by packing with a gauze wick. Aggressive probing of the cavity should be avoided as it can lead to iatrogenic fistulas.

Regular review and dressing change should continue until healing is confirmed. The concern for the emergency physician is to identify those that can be safely drained in the ED without harming continence, causing seeding infection, or missing another diagnosis. Antibiotics are ineffective, and are only indicated in patients with valvular or rheumatic heart disease, diabetes, immunosuppression, extensive cellulitis or a prosthetic device.

Traditionally, in acute perianal abscesses the search for a fistulous internal opening followed by fistulotomy has been the standard treatment.

Although fistulas Opens in new window are often present, immediate management of associated fistula tracts may result in higher rates of further fistulas, incontinence, and unnecessary treatment of fistulas that will resolve spontaneously and not require treatment. Simple drainage is thus advocated for acutes abscesses as in most cases this will be the only treatment required. The risk of recurrence is low.