Diagnosis

Anorectal abscess

Infection arising in the cryptoglandular epithelium lining the anal canal. The infection may extend to the:

  • Intersphincteric space: Perianal abscess (superficial, 60%) [cqi][4c7]

  • Ischiorectal space: Ischiorectal abscess (deeper, 20%) [4c7]

  • Supralevator space (5%) [4c7]

Also known as: Anal abscess, Ischiorectal abscess, Perianal abscess, Perirectal abscess, Rectal abscess

Etiology

Etiology [kh4][cqi]

  1. Anaerobes: Bacteroides fragilis, Peptostreptococcus, Prevotella, Fusobacterium, Porphyromonas, and Clostridium,

  2. Aerobes: Staphylococcus aureus, Streptococcus, and Escherichia coli

  3. Other underlying conditions - 10%: inflammatory bowel disease, trauma, HIV, malignancy, tuberculosis, hidradenitis suppurativa, sexually transmitted diseases, radiation therapy, foreign bodies, perforated diverticular disease

Pathophysiology [kh4]

  1. Abscess formation due to obstruction of anal crypts (90%) [cqi]

  2. Other underlying causes (10%)

  3. The abscess forms initially in the intersphincteric space and then spreads along adjacent spaces

Risk factors

Complications [4c7]

Epidemiology

Incidence per 100.000 [swq][w1f]

Epidemiology chart for Incidence

Symptoms & findings

Symptoms

Chills, Dyschezia, Fever, Malaise

Clinical findings

Elevated CRP, Elevated Sedimentation Rate, Leukocytosis

Anamneses

None listed.

Localized findings

Pain
Radiates
Anus
Onset
Subacute (hours)Gradual (days)
Pattern
Constant
Provoked by
Defecation
Severity
Moderate (4-7)Severe (8-10)
Rash
Radiates
Anus
Distribution
Localized
Lesion type
AbscessErythemaPlaque
Color
Red
Associated symptom
BleedingDischargePainSwelling
Palpation
BlanchingFluctantPainWarmth

Approach

Treatment

  1. Incision and surgical drainage [kh4]

  2. Antibiotics if immunosuppression, diabetic, sepsis

  3. Antibiotics alone is inadequate and inappropriate

Differential diagnoses

Anal cancer, Anal fissure, Anorectal fistula, Bartholins abscess, Cellulitis, Colorectal cancer, Constipation, Crohn disease, Diarrhea, Hemorrhoids, Hidradenitis suppurativa, HIV, Immunodeficiency, Necrotizing fasciitis, Periurethral abscess, Pilonidal disease, Proctitis, Prostatic abscess, Rectal prolapse, Ulcerative colitis

References

[1] Sigmon DF, Emmanuel B, Tuma F. Perianal Abscess. [Updated 2023 Jun 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK459167/

[2] Turner SV, Singh J. Perirectal Abscess. [Updated 2023 Aug 7]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507895/

[3] https://emedicine.medscape.com/article/191975

[4] Hsieh et al. Epidemiology and outcomes of anal abscess in patients on chronic dialysis: a 14-year retrospective study. Clinics (Sao Paulo). 2019 Mar 21;74:e638.

[5] Abcarian H. Anorectal infection: abscess-fistula. Clin Colon Rectal Surg. 2011 Mar;24(1):14-21. doi: 10.1055/s-0031-1272819.

[6] Sainio P. Fistula-in-ano in a defined population. Incidence and epidemiological aspects. Ann Chir Gynaecol. 1984;73(4):219-24.

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