eMedicine Specialties > Pediatrics: Surgery > General Surgery

Perianal and Perirectal Abscesses

Author: Asma Al Mannaie, MBBS, Acting Chair, Health Education Section, Preventive Medicine Department, Health Authority of Abu Dhabi, UAE
Coauthor(s): Pramod S Puligandla, MD, MSc, FRCSC, Assistant Professor of Surgery and Pediatrics, McGill University Health Centre; Consulting Staff, Divisions of Pediatric Surgery and Pediatric Critical Care, Montreal Children's Hospital/Research Institute
Contributor Information and Disclosures

Updated: Aug 29, 2006

Introduction

A perianal abscess is one of the common complaints seen in the field of pediatric surgery. It occurs most often in infants younger than 1 year. However, its exact prevalence and incidence is not well established.

Perianal abscesses are defined as collections of pus outside the anus, which start as an infection in the anal crypt glands. The abscess often appears as a raised, red lesion under the skin lateral to the anus, where it may grow and become painful. Some abscess may spontaneously drain pus and heal, whereas others may require surgical intervention. Despite its relatively simple nature, a perianal abscess can cause significant morbidity if improperly treated.

Frequency

Although the precise incidence of perianal and perirectal abscesses is not known, approximately 0.5-4.3% of all abscess occur in children.

No racial predilection is reported, and the condition may occur in any age group.

In infants, the distribution is equal among boys and girls. However, in younger than 2 years, these abscesses occur more frequently in boys.

Approximately 57-86% of patients with perianal abscess present before 1 year of age.

Etiology

In most cases, particularly in infants, perianal and perirectal abscess thought to be secondary to abnormal anal crypt formation. Although the exact etiology for abnormal crypt formation is unclear, some have suggested that androgen excess or androgen-estrogen imbalance might predispose an individual to the formation of abnormal crypts of Morgagni and a tendency to develop cryptitis and/or abscess.

Pathophysiology

The development of a perianal abscess can be divided into an acute phase (abscess) and a chronic phase (fistula-in-ano).

The vast majority of the perianal abscesses and fistulas originate from infected anal crypt glands. The infection then penetrates the internal sphincter and spreads into the intersphincteric space.

The etiology of abnormal crypt formation is still unidentified. Interestingly, the crypts of infants with fistulas tend to be deeper (3-10 mm) than those in healthy infants (1-2 mm). Such observations support the hypothesis of a congenital anomaly as the basis for perianal abscess formation in infants.

Presentation

Patients often present within the first few months of life. Perianal abscesses can appear as red, swollen, tender areas lateral to the anus. The child may be irritable or hold his or her bowel movements.

Elements in the history that are suggestive of perianal abscess include constipation, fever, painful defecation, refusal to walk, and rectal pain. Weight loss, failure to thrive, diarrhea, and abdominal pain are the symptoms associated with Crohn disease, for which perianal disease may be a presenting symptom.

Infants with perianal abscesses generally do not have underlying medical conditions that predispose them to abscesses. Superficial lesions may occur secondary to an infected diaper rash. Most abscesses are self-limited and spontaneously drain and resolve without surgical intervention. However, as many 50% can progress to fistula-in-ano with chronic drainage. For lesions that persist, a fistulotomy is required.

For older children, 52% of perianal abscess may be secondary to an underlying medical condition. Such conditions include inflammatory bowel disease (IBD) disease (especially Crohn disease), immunocompromised states (due to leukemia, AIDS, medications), diabetes, and foreign body or external trauma. Abscesses may also be seen as sequelae of surgical intervention for Hirschsprung disease or imperforate anus.

Antibiotics play a limited role in the primary therapy of perianal abscesses.

Indications

The usual treatment of perianal abscess is incision and drainage. In infants, this procedure can be performed with local, topical anesthetic. General anesthesia may be required for older children.

Without intervention, as many as 85% of children with perianal abscess present with a recurrent abscess or progression to fistula.

Patients with perianal abscesses that recur after adequate incision and drainage require an examination under anesthesia to identify the fistula. Recurrent, nonhealing, complex, or multiple abscess and fistulas may indicate Crohn disease. Appropriate investigations should be initiated to rule out this possibility.

Relevant Anatomy

Most abscesses and fistulas are lateral to the anus. The infection generally begins in the anal crypts, where it penetrates the intersphincteric space. The infection may then extend to the perianal skin or superiorly within the intersphincteric space.

Patients with complex abscesses involving the ischiorectal space or the contralateral side of the anus (horseshoe abscess) need to be thoroughly evaluated for Crohn disease. This is especially true for patients with abscesses extending above the levator ani (supralevator). Patients with nonhealing and recurrent abscesses and/or fistulas should undergo further evaluation as well.

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