Perianal and Perirectal Abscess

Perianal and perirectal abscesses are collections of pus in the enclosed space near the perirectal tissues. These infections originate from obstruction of anal crypt glands. Patients present with severe pain in the anal or rectal area. Finding a tender, fluctuant mass on physical exam can provide the diagnosis. Management requires prompt surgical incision and drainage, which may be followed by a course of antibiotics in some cases. Untreated, these abscesses can lead to the formation of fistulas.

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Epidemiology and Etiology

Epidemiology

  • Approximately 100,000 new cases per year in the United States
  • Age:
    • Usually presents between 20 and 60 years of age
    • Mean: 40 years
  • Twice as common in men as in women
  • 30% of patients report a prior history of anorectal abscess.

Etiology

Infection of an obstructed glandular crypt may occur due to:

  • Nonspecific obstruction (approximately 90% of cases)
  • Inflammatory bowel disease (especially Crohn disease)
  • Trauma
  • Malignancy 
  • Extension of another infection:
    • Diverticulitis
    • Pelvic inflammatory disease

Common bacteria:

  • Escherichia coli
  • Staphylococcus aureus
  • Streptococcus
  • Enterococcus
  • Proteus
  • Prevotella
  • Peptostreptococcus
  • Porphyromonas
  • Fusobacteria
  • Bacteroides
  • Clostridium

Risk factors

  • Immunosuppression:
    • Diabetes
    • Chemotherapy
    • HIV
  • Smoking
  • Rectal prolapse

Classification and Pathophysiology

Classification

The classification of anorectal abscesses is based on their location.

  • Perianal abscess (most common)
  • Ischiorectal
  • Intersphincteric
  • Supralevator

Locations of perianal, ischiorectal, intersphincteric, and supralevator abscesses

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Pathophysiology

  • Obstruction of an anal crypt gland allows bacterial growth → abscess
  • The abscess can spread along planes to:
    • Intersphincteric, ischiorectal, or supralevator spaces → perirectal abscess
    • Perianal skin → perianal abscess

Clinical Presentation and Diagnosis

Symptoms

The symptoms of a perirectal or perianal abscess can vary based on its location, but may include:

  • Anal or rectal symptoms:
    • Pain:
      • Severe
      • Constant  
      • Dull, sharp, aching, or throbbing
      • May be exacerbated by bowel movements or sitting
    • Constipation or diarrhea
    • Purulent drainage
    • Rectal bleeding
  • Constitutional symptoms:
    • Fever (21%)
    • Chills
    • Malaise
    • Fatigue

Physical exam

  • Perianal swelling and erythema may be seen.
  • Depending on the location, external or digital rectal exam may reveal:
    • Swelling
    • Tenderness
    • Fluctuance
  • Spontaneous drainage may be bloody or purulent.

Diagnosis

The diagnosis of a perirectal or perianal abscess is made clinically. However, CT, MRI, or ultrasonography may be useful for identifying:

  • A deep abscess
  • A potential intra-abdominal source of infection

Management and Complications

Management

Surgical drainage: 

  • Standard of care
  • All anorectal abscesses should be drained promptly.
  • A simple, perianal abscess can be drained in an office or ED.
  • Complex perirectal abscesses require drainage in an OR.

Antibiotic therapy:

  • Options:
    • Amoxicillin–clavulanate
    • Ciprofloxacin plus metronidazole
  • Indications:
    • Extensive cellulitis
    • Signs of sepsis
    • Valvular heart disease
    • Immunosuppression
    • Diabetes 

Postoperative care: 

  • Keep incision site clean.
  • Analgesics
  • Stool softeners
  • Sitz baths

Complications

  • Sepsis
  • Recurrent abscess
  • Fistula formation
  • Urinary retention
  • Constipation or incontinence
  • Fournier gangrene: 
    • Necrotizing fasciitis of the external genitalia, perineal, or perianal area
    • Associated with a high rate of mortality

Differential Diagnosis

  • Anal fissure: a superficial tear in the anoderm associated with constipation, trauma or inflammatory bowel disease: Patients present with rectal pain during bowel movements, passage of bright red blood, and anal spasm. The diagnosis is clinical. Management is usually conservative and includes increasing fluid and fiber intake, warm sitz baths, and stool softeners. Topical nifedipine helps with anal spasms, and local anesthetics provide pain control.  
  • Anal fistula: abnormal communications between the anorectal lumen and another body structure, often to the skin: Anal fistula can occur because of extension of an anal abscess. Symptoms include pain and abnormal discharge. The diagnosis is clinical. Management is primarily surgical (fistulotomy) but can include antibiotics if infection is present.
  • Hemorrhoids: dilated vessels of the hemorrhoidal plexus in the anal canal, commonly caused by constipation: Depending on the location of the veins, hemorrhoids can be internal or external. External hemorrhoids are painful, whereas internal hemorrhoids are painless. Both types can bleed and appear as a soft rectal mass on exam. The diagnosis is clinical. Management includes stool softeners, topical hydrocortisone, and sitz baths. Additional treatment options are rubber band ligation or surgical removal.  
  • Pilonidal cyst: can present as an abscess: Like perianal abscesses, pilonidal cysts present with erythema, tenderness, and swelling. However, pilonidal abscesses occur in the intergluteal area superior and dorsal to the anus. These cysts are diagnosed by physical examination and are treated by surgical incision and drainage.  
  • Anal carcinoma: neoplastic disease in which cancer cells form and grow in the anus: Risk factors include older age, infections such as HPV, multiple sexual partners, and anal sex. Symptoms include bleeding from the anus, anal pain, anal mass, or itching. Anal carcinoma is diagnosed by biopsy. Management can include surgery, radiation, or chemotherapy.

References

  1. Bleday R (2020). Perianal and perirectal abscesses. UpToDate. Retrieved March 14, 2020, from https://www.uptodate.com/contents/perianal-and-perirectal-abscess
  2. Kumar V, Abbas AK, Aster JC. (2015). Robbins & Cotran Pathologic Basis of Disease. Philadelphia: Elsevier Saunders.
  3. Sigmon DF, Emmanuel B, Tuma F. (2020). Perianal abscess. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK459167/
  4. Turner SV, Singh J. (2020). Perirectal abscess. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK507895/
  5. Whiteford MH (2007). Perianal abscess/fistula disease. Clinics in Colon and Rectal Surgery 20(2):102–109. https://doi.org/10.1055/s-2007-977488
  6. Ansari P (2021). Anorectal abscess. MSD Manual Professional Version. Retrieved April 1, 2021, from https://www.msdmanuals.com/professional/gastrointestinal-disorders/anorectal-disorders/anorectal-abscess

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