A perirectal abscess is a localized inflammatory process that can be associated with infections of soft tissue and anal glands based on anatomic location. Perianal and perirectal abscesses may be simple or complex, causing suppuration. Infections in these spaces may be classified as superficial perianal or perirectal with involvement in the following anatomic spaces: Ischiorectal, intersphincteric, perianal, and supralevator. The Parks classification of anorectal abscess is subdivided into intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric abscess (Fig. 1).

Rectal abscess

Perianal abscess

Anorectal abscess

• Localized perirectal or anal pain-often worsened with movement or straining
• Perirectal erythema or cellulitis
• Perirectal mass by inspection or palpation
• Fever and signs of sepsis with deep abscess
• Urinary retention

• Polymicrobial aerobic and anaerobic bacteria involving one of the anatomic spaces (see “Definition”), often associated with localized trauma
• Microbiology: Most infections are polymicrobial, mixed enteric, and skin flora
• Predominant anaerobic bacteria:
  1. Bacteroides fragilis
  2. Peptostreptococcus spp.
  3. Prevotella spp.
  4. Porphyromonas spp.
  5. Clostridioides spp.
  6. Fusobacterium spp.
• Predominant aerobic bacteria:
  1. Staphylococcus aureus
  2. Streptococcus spp.
  3. Escherichia coli
  4. Enterococcus spp.

• Neutropenic enterocolitis
• Crohn disease (inflammatory bowel disease)
• Pilonidal disease
• Hidradenitis suppurativa
• Tuberculosis or actinomycosis; Chagas disease
• Cancerous lesions
• Chronic anal fistula
• Rectovaginal fistula
• Proctitis-often STD-associated, including syphilis, gonococcal, chlamydia, chancroid, condylomata acuminata
• AIDS-associated: Kaposi sarcoma, lymphoma, cytomegalovirus

• Examination of rectal, perirectal/perineal areas
• Rule out necrotic process and crepitance suggesting deep tissue involvement
• Local aerobic and anaerobic culture
• Blood cultures if toxic, febrile, or compromised
• Possible sigmoidoscopy

Usually not indicated unless extensive disease is suspected. CT has a sensitivity of 77% and is relatively poor in detecting a perirectal abscess in immunocompromised patients.

• Incision and drainage of abscess
• Debridement of necrotic tissue
• Rule out need for fistulectomy
• Local wound care-packing
• Sitz baths
• Antibiotic treatment: Directed toward coverage for mixed skin and enteric flora

Follow-up with a general surgeon or infectious disease physician is often warranted.

• General surgeon or colorectal surgeon for drainage.
• AIDS specialist may be needed for perirectal complications of HIV infection.
• Gastroenterologist follow-up may be warranted in Crohn disease with perirectal fistula and other complications.
• Endoscopic ultrasound-guided perirectal abscess drainage is a recently described promising alternative treatment.

Perirectal Abscess (Patient Information)