Perirectal Abscess And Fistula

A perirectal abscess is a localized collection of pus caused by inflammation of the soft tissue outside the anal verge. Such inflammation may produce a fistula in and - an abnormal opening in the anal skin - that may communicate with the rectum. Men are affected by this disease three times as often as women.

Causes

The inflammatory process that leads to abscess may begin with an abrasion or tear in the lining of the anal canal, rectum, or perianal skin, and subsequent infection by Escherichia coli, staphylococci, or streptococci. Such trauma may result from injections for treatment of internal hemorrhoids, enema-tip abrasions, puncture wounds from ingested eggshells or fishbones, or insertion of foreign objects.

Other preexisting lesions include infected anal fissure, infections from the anal crypt through the anal gland, ruptured anal hematoma, prolapsed thrombotic internal hemorrhoids, and septic lesions in the pelvis, such as acute appendicitis, acute salpingitis, and diverticulitis. Systemic illnesses that may cause abscesses include ulcerative colitis and Crohn's disease. However, many abscesses develop without preexistinglesions. Other causes include trauma, malignancy, radiation, infectious dermatitis, and an immunocompromised state.

As the abscess produces more pus, a fistula may form in the soft tissue beneath the muscle fibers of the sphincters (especially the external sphincter), usually extending into the perianal skin. The internal (primary) opening of the abscess or fistula is usually near the anal glands and crypts; the external (secondary) opening, in the perianal skin.

Signs and symptoms

Characteristics are throbbing pain and tenderness at the site of the abscess and painful swelling that is exacerbated by defecation. A hard, painful lump develops on one side, preventing comfortable sitting.

Diagnosis

Perirectal abscess is detectable on physical examination:

• Perianal abscess is a red, tender, localized, oval swelling close to the anus. Sitting or coughing increases pain, and pus may drain from the abscess. Digital examination reveals no abnormalities.
• Ischiorectal abscess involves the entire perianal region on the affected side of the anus. The only symptom of this large erythematous, indurated, tender mass at the buttock may be pain. It's tender but may not produce drainage. Digital rectal examination reveals a tender induration bulging into the anal canal.

CLINICAL TIP

A flexible sigmoid oscopy should be performed at a later date on these patients to rule out carcinoma or inflammatory bowel disease.

• Submucous or high intermuscular abscess may produce a dull, aching pain in the rectum, tenderness and, occasionally, induration. Digital examination reveals a smooth swelling of the upper part of the anal canal or lower rectum.
• Pelvirectal abscess (rare) produces fever, malaise, and myalgia but no local anal or external rectal signs or pain. Digital examination reveals a tender mass high in the pelvis, perhaps extending into one of the ischiorectal fossae.
• If the abscess drains by forming a fistula, the pain usually subsides and the major signs become pruritic drainage and subsequent perianal irritation.

CLINICAL TIP

Pain and discharge are symptoms of fistula development and when the external or secondary opening has closed.

The external opening of a fistula generally appears as a pink or red, elevated, discharging sinus or ulcer on the skin near the anus. Depending on the infection's severity, the patient may have chills, fever, nausea, vomiting; and malaise. Digital rectal examination may reveal a palpable indurated tract and a drop or two of pus on palpation. The internal opening may be palpated as a depression or ulcer in the midline anteriorly or at the dentate line posteriorly. To identify an internal opening, an examination under anesthesia should be performed.

Flexible sigmoidoscopy, barium studies, and colonoscopy should be performed to rule out underlying conditions.

Treatment

Perirectal abscesses require surgical incision and drainage. The area may be explored to identify a fistula tract, and a fistulotomy may be performed at a later date. Fistulas require a fistulotomy - removal of the fistula tract and associated granulation tissue­under general, spinal, or caudal anesthesia. If the fistula tract is epithelialized, treatment requires fistulectomy­removal of the fistulous tract-followed by insertion of drains, which are gradually removed over time.