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, pestianal, and supraelevator

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 above anatomic spaces, often associated with localized trauma.

Microbiology: most bacteria are polymicrobial, mixed enteric and skin flora

Predominant anaerobic bacteria:

• Bacteroides fragilis
• Peptostreptococcus spp.
• Prevotella spp.
• Fusobacterium spp.
• Porphyromonas spp.
• Clostridium spp.
Predominant aerobic bacteria:

• Staphylococcus aureus
• Streptococcus spp.
• Escherichia coli

Many patients will have predisposing underlying conditions including:
• Malignancy or leukemia
• Immune deficiency
• Diabetes mellitus
• Recent surgery
• Steroid therapy

• Neutropenic enterocolitis
• Crohn’s 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’s sarcoma
Lymphoma
CMV

WORKUP

• 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
IMAGING STUDIES
Usually not indicated unless extensive disease abscess

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

Outpatient—oral:
Amoxacillin clavulanic acid (Augmentin)
Ciprofloxacin plus metronidazole or clindamycin
Inpatient—intravenous:
Ampicillin/sulbactam (Unasyn)
Cefotetan
Piperacillin/tazobactam
Imipenem

Nelson RL et al: Prevalence of benign anorectal disease in a randomly selected population, Dis Colon Rectum 88:341, 1994.

Nomikos IN: Anorectal abscesses: need for accurate anatomical localization of the disease, Clin Anat 10:239, 1997.