AKT · Gastroenterology/Colon & rectum

Toxic megacolon

Acute non-obstructive colonic dilatation + systemic toxicity (severe colitis: UC, C. diff, ischaemic)

Overview

A life-threatening complication of severe colitis — acute non-obstructive dilatation of the colon (transverse colon >6 cm) with systemic toxicity. Causes: acute severe ulcerative colitis (and Crohn), C. difficile, ischaemic/infective colitis. Risks perforation and death. Managed with aggressive medical therapy and urgent surgery (colectomy) if no improvement; antimotility agents and colonoscopy are avoided.

Recognise

Severe colitis (bloody diarrhoea) with abdominal distension, pain, fever, tachycardia, dehydration and systemic toxicity
AXR: dilated TRANSVERSE colon (>6 cm) ± mucosal islands/thumbprinting; reduced bowel sounds
Often precipitated by antimotility/opioid drugs, hypokalaemia, or colonoscopy in acute severe colitis

Red flags

Perforation (sudden deterioration, free air, peritonitis) → emergency colectomy
No improvement on medical therapy within ~24–72 h → colectomy

Differentials & how to tell them apart

Large bowel obstructionmechanical cause (cancer/volvulus) with a transition point — toxic megacolon is non-obstructive with colitis

Pseudo-obstruction (Ogilvie)colonic dilatation without colitis/mechanical obstruction — often post-op/elderly

Sigmoid volvuluscoffee-bean loop, closed-loop obstruction

Toxic megacolon — dilated transverse colon (>6 cm) with mucosal oedema (AXR)
Hellerhoff / CC BY-SA 4.0 — Wikimedia Commons

Investigations

AXR (transverse colon >6 cm — diagnostic); FBC/U&Es (hypokalaemia)/CRP/lactate; blood cultures; C. diff testing. AVOID colonoscopy (perforation risk).

Management

Resuscitation + IV steroids/antibiotics; urgent colectomy if no improvement/perforation

1Resuscitate (fluids, correct potassium); treat the cause (IV corticosteroids for UC, treat C. diff); IV antibiotics; stop antimotility/opioid drugs; AVOID colonoscopy. Serial AXR and clinical review.Gate: If there is perforation, or NO improvement on maximal medical therapy within ~24–72 h, proceed to urgent COLECTOMY — don't persist with medical treatment; antimotility agents and colonoscopy can precipitate it
2Subtotal colectomy for failure/perforation; ongoing critical care; address the underlying colitis.

Aggressive resuscitation + IV corticosteroids (if IBD) — fluids, electrolytes (correct potassium), IV steroids for UC; treat C. diff

IV antibiotics; stop antimotility/opioid drugs — and avoid colonoscopy

Urgent colectomy — if perforation or no improvement on medical therapy

Key points

Severe colitis + distension + systemic toxicity + transverse colon >6 cm on AXR = toxic megacolon → resuscitate, treat the cause, and colectomy if not improving. No loperamide, no colonoscopy.

Monitor & prognosis

Serial AXR, observations, lactate; surgical threshold.

High mortality if perforation; good if treated promptly.

Source: NICE NG130 (UC); ACPGBI