Perianal abscesses and fistulae ✅

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

📌 Perianal Abscesses & Fistulae – NICE-Aligned Summary

Perianal abscesses and fistulae are common anorectal conditions arising from infection of the anal glands (cryptoglandular). A perianal abscess is an acute collection of pus, whereas a fistula-in-ano is a chronic tract between the anal canal and perianal skin. If untreated, abscesses may evolve into fistulae, causing recurrent sepsis and discharge. Early recognition and appropriate surgical intervention improve outcomes, particularly in high-risk groups such as patients with Crohn’s disease, diabetes, or immunosuppression.

💥 Perianal Abscess

A perianal abscess is a surgical emergency. Incision and drainage (I&D) is the first-line treatment. NICE recommends drainage under appropriate anaesthesia, with antibiotics reserved for patients who are immunocompromised, systemically unwell, or have extensive cellulitis.

Causes

• 🔹 Cryptoglandular infection – most common
• 🔹 Inflammatory bowel disease (Crohn’s disease) – predisposes to recurrent abscesses
• 🔹 Trauma or surgery – e.g., fissures, haemorrhoidectomy
• 🔹 Immunosuppression – diabetes, HIV, corticosteroids

🩺 Clinical Features

• ⚡ Severe perianal pain, worse on sitting
• 🔴 Red, tender, warm swelling near the anus
• 🌡️ Fever / systemic upset in advanced infection
• 💧 Spontaneous pus discharge if ruptured

Diagnosis

• 👀 Clinical examination and digital rectal exam (DRE) usually sufficient
• 🧲 MRI pelvis or endoanal ultrasound if deep or complex abscess suspected

💊 Management

• ✂️ Incision & drainage – gold standard
• 💊 Antibiotics only if immunocompromised, septic, or extensive cellulitis
• 💊 Analgesia: NSAIDs or opioids
• 🔎 Follow-up: monitor for fistula formation (30–50% risk)

🔄 Perianal Fistula

A perianal fistula is a chronic tract connecting the anal canal to perianal skin. It often follows a drained abscess, causing persistent discharge or recurrent infection. Management is usually surgical, with the approach tailored to fistula type and sphincter involvement.

Causes

• 🔹 Post-abscess formation – most common
• 🔹 Crohn’s disease – higher risk of complex, multiple fistulae
• 🔹 Trauma / surgery – including obstetric injury
• 🔹 Chronic infection – persistent cryptoglandular sepsis

🩺 Clinical Features

• ♻️ Recurrent abscesses with swelling
• 💧 Intermittent pus or faecal discharge from skin opening
• ⚡ Pain, especially if the tract becomes infected

Classification (Parks System)

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

Diagnosis

• 👀 Exam: external opening, induration, discharge
• 🧲 MRI pelvis: gold standard for complex fistula mapping
• 🔦 Endoanal ultrasound: alternative imaging
• 🪡 Probing under anaesthesia: defines tract course

💊 Management

• 🔧 Surgical options:
• ✂️ Fistulotomy – unroofing simple, low tracts
• 🧵 Seton placement – drains sepsis, preserves sphincter
• 🩹 Advancement flap – closes internal opening with tissue flap
• 🔗 LIFT procedure – sphincter-sparing ligation of intersphincteric tract
• 💊 Antibiotics: especially in Crohn’s disease or sepsis
• 💊 Analgesia & stool softeners: reduce discomfort and strain

📌 Conclusion

Perianal abscesses and fistulae are interlinked conditions of cryptoglandular infection. Early surgical drainage of abscesses and tailored fistula surgery minimise recurrence. Patients with Crohn’s disease may need combined medical–surgical management for optimal outcomes.

📚 NICE References

• NICE NG144: Anal Fistula: Diagnosis and Management (2019)
• NICE CG139: Crohn's Disease: Management (2012, updated 2019)
• NICE pathway: Anal abscess & fistula