Perianal abscesses and fistulae

Related Subjects: |Rectal Prolapse |Anal Cancer |Anal Fissure |Perianal abscesses and fistulae |Pilonidal Abscess (sinus) |Haemorrhoids (Piles)

Perianal abscesses and fistulae are common anorectal conditions, both arising from infection of anal glands within the crypts of Morgagni. A perianal abscess is an acute collection of pus, while a fistula represents a chronic abnormal tract between the anal canal and perianal skin. If untreated, an abscess may evolve into a fistula, creating a cycle of recurrent sepsis and discharge.

💥 Perianal Abscess

A perianal abscess is a painful, pus-filled cavity around the anus due to infected anal glands. It is a surgical emergency: incision and drainage is the mainstay of treatment.

Causes

• 🔹 Cryptoglandular infection – most common mechanism.
• 🔹 IBD (Crohn’s disease) – predisposes to recurrent abscesses.
• 🔹 Trauma or surgery – anal fissures, haemorrhoidectomy.
• 🔹 Immunosuppression – diabetes, HIV, steroids increase risk.

🩺 Clinical Features

• ⚡ Severe, constant, throbbing perianal pain, worse on sitting.
• 🔴 Red, warm swelling near the anus.
• 🌡️ Fever and systemic upset in advanced infection.
• 💧 Possible spontaneous pus discharge if ruptured.

Diagnosis

• 👀 Clinical exam and DRE: tender, fluctuant swelling.
• 🧲 MRI pelvis or ultrasound if a deeper abscess suspected.

💊 Management

• ✂️ Incision & Drainage (I&D): gold-standard treatment.
• 💊 Antibiotics: only if immunocompromised or septic.
• 💊 Analgesia: NSAIDs or opioids for pain control.
• 🔎 Follow-up: watch for fistula formation (30–50% risk).

🔄 Perianal Fistula

A perianal fistula is a chronic abnormal tract between the anorectal canal and perianal skin. It often follows a drained abscess, and may cause persistent discharge or recurrent infection.

Causes

• 🔹 Post-abscess: most common cause after drainage.
• 🔹 Crohn’s disease: high risk of multiple, complex fistulae.
• 🔹 Trauma / Surgery: including obstetric trauma.
• 🔹 Chronic infection: persistent cryptoglandular sepsis.

🩺 Clinical Features

• ♻️ Recurrent abscesses with swelling and pus.
• 💧 Discharge: intermittent pus or fecal matter from a skin opening.
• ⚡ Pain: especially if the tract becomes infected.

Classification (Parks System)

• ➡️ Intersphincteric: tract runs between internal & external sphincters (most common).
• ➡️ Transsphincteric: passes through both sphincters.
• ➡️ Suprasphincteric: arches above external sphincter.
• ➡️ Extrasphincteric: rare, tract bypasses sphincters entirely.

Diagnosis

• 👀 Exam: external opening, induration, discharge.
• 🧲 MRI pelvis: gold standard to delineate complex tracts.
• 🔦 Endoanal ultrasound – alternative imaging modality.
• 🪡 Probing under anaesthesia to map tract course.

💊 Management

• 🔧 Surgery is definitive:
  • ✂️ Fistulotomy: unroofing simple, low tracts.
  • 🧵 Seton placement: drains sepsis, preserves sphincter.
  • 🩹 Advancement flap: closes internal opening with tissue flap.
  • 🔗 LIFT procedure: (Ligation of Intersphincteric Fistula Tract) – sphincter-sparing.
• 💊 Antibiotics: especially in Crohn’s disease.
• 💊 Analgesia & stool softeners: reduce strain and discomfort.

📌 Conclusion

Perianal abscesses and fistulae are interlinked conditions of cryptoglandular infection. Abscesses demand urgent surgical drainage, while fistulae usually require definitive surgery tailored to their course. Early recognition, imaging, and appropriate surgical choice improve outcomes and minimise recurrence, while Crohn’s-associated fistulae often need combined medical–surgical management.