Toxic megacolon
Toxic megacolon is acute non-obstructive colonic dilatation accompanied by systemic toxicity, usually complicating acute severe ulcerative colitis or severe infection such as C. difficile; it is a time-critical colorectal emergency because the inflamed colon can perforate.
Definition
Toxic megacolon is acute non-obstructive dilatation of the colon accompanied by systemic toxicity, usually in severe colitis. A transverse-colon diameter above about 6 cm is the established radiographic teaching threshold, but the clinical syndrome is defined by dilatation plus systemic illness and carries a risk of perforation.
First principles
Dilatation and systemic toxicity must occur together
A large colon on imaging alone is not toxic megacolon. The syndrome requires acute non-obstructive colonic dilatation together with systemic toxicity such as fever, tachycardia, leucocytosis, anaemia, hypotension, dehydration or confusion. A transverse-colon diameter above about 6 cm is the established radiographic teaching threshold, but the diameter must be interpreted with the whole clinical picture and should never delay surgical escalation.
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