Colonic Distension in Toxic Megacolon is Most Prominent in the Transverse Colon
In toxic megacolon, colonic distension is most prominent in the transverse colon (answer c). 1
Pathophysiology and Anatomical Distribution of Distension
- Unlike colonic obstruction where cecal dilation and perforation are primary concerns, in toxic megacolon the transverse colon is the area of greatest concern for dilation and potential perforation 1
- Toxic megacolon is characterized by radiographic evidence of total or segmental colonic distention of > 6 cm, presence of systemic toxicity, and inflammatory (or infectious) etiology 1
Diagnostic Features of Toxic Megacolon
- Radiographic findings typically show transverse colon dilation and loss of haustrations, with mean diameter measurements of approximately 9-10 cm 2
- Plain abdominal radiographs are an acceptable first study to detect toxic megacolon, defined by a mid-transverse colonic dilation > 5.5 cm 1
- CT scanning can provide additional information and is particularly useful for detecting complications such as perforation, abscess formation, or thrombosis 1, 3
Clinical Significance of Transverse Colon Involvement
- Perforation in the transverse colon of patients with toxic megacolon is associated with a high mortality rate (27-57%), regardless of whether the perforation is contained or free 1
- The predilection for transverse colon involvement necessitates close monitoring of colonic diameter progression, as increasing dilation is an indication for urgent surgical intervention 1
Management Implications
- Management requires coordination between medical and surgical services with aggressive medical therapy and early surgical intervention if there's no improvement or if complications develop 1
- Persistent fever after 48-72 hours of steroid therapy should raise suspicion for local perforation or abscess formation 1
- Indications for urgent surgery include free perforation, massive hemorrhage, increasing transfusion requirements, increasing signs of toxicity, and progression of colonic dilatation 1
- Medical decompression techniques, including positioning patients in prone position ("rolling technique"), have been reported to help redistribute colonic gas and promote decompression 4
Etiology and Risk Factors
- Most commonly associated with inflammatory bowel disease (ulcerative colitis or ileocolonic Crohn's disease) but can also occur with infectious causes like Clostridium difficile colitis 1, 5
- Predisposing factors include antibiotics, immunosuppressants, chemotherapy, and antidiarrheal medications 2
- The condition requires prompt recognition as it carries significant morbidity and mortality if not managed appropriately 3, 6