Anorectal Abscess

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Anorectal abscess is a localised collection of pus in the perianal or rectal area, resulting from infection of the anal glands. It is a painful and potentially serious condition that may lead to complications such as a fistula formation.

Aetiology

The condition arises due to obstruction and subsequent infection of the anal crypt glands, leading to abscess formation. Common causes include:

  • Bacterial infections: most commonly caused by Escherichia coli, Staphylococcus aureus, Bacteroides, and Enterococcus species.
  • Cryptoglandular theory: obstruction of anal glands leading to bacterial overgrowth and abscess formation.
  • Underlying conditions: such as Crohn’s disease, diabetes mellitus, or immunosuppression.
  • Trauma: including anal fissures or surgery.

Pathophysiology

  • Bacteria enter the anal glands, leading to localised inflammation and pus formation.
  • If untreated, the infection spreads to deeper perianal tissues, forming larger abscesses.
  • In some cases, the abscess drains spontaneously or progresses to an anal fistula.

Risk factors

  • Inflammatory bowel disease (Crohn’s disease, ulcerative colitis).
  • Diabetes mellitus (increased risk of infections).
  • Immunosuppression (HIV, chemotherapy, steroid use).
  • Obesity.
  • Anal trauma or previous anorectal surgery.
  • Chronic diarrhoea or constipation.

Signs and symptoms

  • Perianal pain: constant, throbbing pain that worsens with movement or sitting.
  • Perianal swelling: red, tender, warm lump near the anus.
  • Pus discharge: if the abscess ruptures spontaneously.
  • Fever and malaise: suggests systemic infection.
  • Fluctuant mass on examination: sign of pus collection.

Investigations

  • Clinical diagnosis: based on history and examination.
  • Ultrasound or MRI pelvis: used for deep abscesses or suspected fistulas.
  • Blood tests: raised white cell count and CRP if systemic infection is present.
  • Swab for culture: in immunocompromised patients or recurrent infections.

Management

1. Incision and Drainage (definitive Treatment):

  • Surgical drainage: performed under local or general anaesthesia.
  • Wide drainage: to prevent recurrence.
  • Packing of the cavity: sometimes needed to aid healing.

2. Antibiotics:

  • Not routinely required unless there is cellulitis, systemic infection, or immunosuppression.
  • If indicated, broad-spectrum antibiotics such as co-amoxiclav or metronidazole are used.

3. Pain Management:

  • Simple analgesia (paracetamol, ibuprofen).
  • Warm sitz baths for pain relief.

4. Prevention of Recurrence:

  • Treat underlying conditions (e.g., Crohn’s disease).
  • Good perianal hygiene.
  • High-fibre diet to prevent constipation.
  • Monitor for fistula formation.
GastroenterologymypanotesAnorectal Abscess