Toxic Megacolon

Published on 09/08/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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 Transverse colonic folds may be thickened (edema or hemorrhage), or lost (sloughed mucosa and submucosa)

TOP DIFFERENTIAL DIAGNOSES

• Colonic obstruction or Ileus

image Preservation of mucosal and transverse fold pattern

PATHOLOGY

• Clostridium difficile and other infectious colitis

image Now the most common etiology
image Ulcerative colitis was more common in past

CLINICAL ISSUES

• Most severe, life-threatening complication of colitis
• Most common signs/symptoms

image Patients appear “toxic,” very ill
image Fever, pain, abdominal distension, bloody diarrhea
image Complications: Perforation, peritonitis, death
• Other signs/symptoms

image Lab data: Increased WBC and ESR; positive fecal occult blood test
• Treatment: Colectomy and treatment of complications
• Prognosis: Good following colectomy without perforation

image Poor if colonic perforation and sepsis precede colectomy
• Seen in ∼ 5% of infectious or ulcerative colitis patients

DIAGNOSTIC CHECKLIST

• Consider prior history of infectious or ulcerative colitis
• Dilated colon with air-fluid levels; thickened or absent transverse folds in a very sick patient
image
(Left) Supine radiograph in a 58-year-old woman, who presented with severe abdominal pain and bloody diarrhea, illustrates the typical appearance of toxic megacolon on plain film. The transverse colon is dilated with marked thickening of the transverse folds image.

image
(Right) This 35-year-old man with a history of ulcerative colitis presents with acute severe abdominal pain and distention. This supine radiograph shows a dilated, ahaustral transverse colon with a “shaggy” surface contour.
image
(Left) This woman developed Clostridium difficile colitis while hospitalized for other reasons. CT shows ascites image, marked dilation of the colon with loss of transverse folds, and intraluminal high-density material image representing hemorrhage and sloughed mucosa.

image
(Right) Axial CECT in the same case shows a generalized ileus image. The colon image is massively distended with blood and debris and its wall is relatively thin. Soon after this scan, the colon perforated and a total colectomy was required.

TERMINOLOGY

Definitions

• Acute transmural fulminant colitis with neuromuscular degeneration and colonic dilation

IMAGING

General Features

• Best diagnostic clue

image Dilated ahaustral colon with pseudopolyps and air-fluid levels
• Location

image Transverse colon > other segments

Radiographic Findings

• Radiography

image Hallmark: Marked colonic dilatation with abnormal or absent fold pattern

– Transverse colon most common ± other segments
– Increased colon caliber on serial radiographs

image > 5 cm on CT, often > 8 cm (as measured on supine radiograph)
– Transverse colonic folds may be thickened (edema or hemorrhage), or lost (sloughed mucosa and submucosa)
– Mucosal islands or pseudopolyps cause irregular surface contour
– Pneumatosis coli ± pneumoperitoneum

CT Findings

• Colon distended with gas, fluid ± blood
• Distorted or absent transverse fold pattern
• Irregular nodular contour of colonic wall (mucosal pseudopolyps)
• ± intramural gas ± blood
• ± free intraperitoneal gas and fluid

Imaging Recommendations

• Best imaging tool

image CECT with multiplanar reformations

DIFFERENTIAL DIAGNOSIS

Colonic Obstruction

• Gas- and stool-filled colon to point of obstruction
• Retained transverse fold and mucosal patterns excludes toxic megacolon

Adynamic or Paralytic Ileus

• Dilated small and large bowel without transition point
• Normal transverse fold pattern excludes toxic megacolon

PATHOLOGY

General Features

• Etiology

image Clostridium difficile and other infectious colitis

– Now the most common etiology
– Ulcerative (and granulomatous) colitis had been more common in past
image Amebiasis, strongyloidiasis, bacillary dysentery
image Typhoid fever, cholera, Behçet syndrome

Gross Pathologic & Surgical Features

• Colon is grossly dilated with fluid and gas
• Wall may appear thinned or thick
• Hemorrhagic necrosis of colonic mucosa and submucosa

image May extend into or through serosa

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Patients appear “toxic,” very ill
image Fever, pain, tenderness, abdominal distension, bloody diarrhea
image Hypotension, sepsis, shock
• Other signs/symptoms

image Lab data: Increased WBC and ESR

Demographics

• Age

image Any age for infectious colitis patients

– 20-35 years for ulcerative colitis patients
• Gender

image M = F
• Epidemiology

image Seen in ∼ 5% of patients with infectious or ulcerative colitis

– Medical and surgical mortality: > 20%
– Most severe, life-threatening complication of colitis

Natural History & Prognosis

• For infectious colitis

image Delayed diagnosis or failed antibiotic therapy may result in toxic megacolon
• For ulcerative colitis, predisposing factors

image Endoscopy; use of opiates and anticholinergic drugs
• Complications: Perforation, peritonitis, death
• Prognosis: Good following colectomy without perforation

image Poor if colonic perforation and sepsis precede colectomy

Treatment

• Colectomy; treat complications

DIAGNOSTIC CHECKLIST

Consider

• Prior history of infectious or ulcerative colitis

Image Interpretation Pearls

• Dilated colon with air-fluid levels; thickened or absent transverse folds in a very sick patient

image
(Left) This 68-year-old woman has longstanding Crohn (granulomatous) colitis with acute exacerbation. This supine film shows marked dilation of the transverse colon with a featureless ahaustral appearance. There is some irregularity of the luminal surface image, suggesting mucosal sloughing or pseudopolyps.
image
(Right) Axial CECT in the same patient shows the colonic dilation and ahaustral appearance with marked thinning of the wall, which suggests a risk of perforation.
image
(Left) A magnified view of the same CT section shows tags of inflamed mucosa or pseudopolyps image within the dilated, thin-walled transverse colon.

image
(Right) Another CT section in the same patient shows fluid image, distention and thinning of the walls of the colon, as well as more mucosal pseudopolyps image.
image
(Left) Axial CECT in the same patient shows similar involvement of the rectosigmoid colon image. Because of symptoms that were refractory to medical management, as well as these CT findings, the patient had a total colectomy.

image
(Right) Gross pathology photograph from a similar patient who underwent colectomy illustrates hemorrhagic necrosis of the colonic mucosa and pseudopolyps image in a case of toxic megacolon.

image
(Left) This 61-year-old man was hospitalized for unrelated reasons and developed acute pain, diarrhea, hypotension, and tachycardia. This supine film shows bulging flanks image due to ascites. The colon is diffusely dilated with a loss of the normal transverse fold pattern. The folds that are seen are grossly thickened and have a “thumbprint” appearance image.
image
(Right) Axial CECT in the same patient shows ascites image and colonic distension image.
image
(Left) Another CT section in the same patient shows that the colon is distended with gas and fluid to a diameter of 7 cm. The mucosa is hyperenhancing and the wall is thickened by submucosal edema image. No normal transverse folds are evident. Ascites fills the paracolic gutters image, accounting for the bulging flanks seen on plain films.

image
(Right) Pelvic CT section in the same patient shows marked fluid distention and wall thickening of the rectosigmoid colon image.
image
(Left) Coronal reformatted CT section in the same patient shows the markedly distended sigmoid colon image with a complete loss of its normal transverse fold pattern.

image
(Right) Another CT section in the same patient confirms the pancolitis image and ascites image. These CT and clinical features are classic for toxic megacolon due to infectious colitis (C. difficile), confirmed at urgent colectomy. The colonic mucosa showed extensive necrosis and sloughing, but no frank perforation was found.
image
Anteroposterior radiograph shows the typical appearance of toxic megacolon with diffuse colonic distention, especially transverse and descending, and the suggestion of wall thickening image due to subserosal and omental edema.

image
Anteroposterior radiograph shows severe and classic toxic megacolon. Note the colonic distention, especially transverse, and the suggestion of pseudopolyps image.
image
Anteroposterior CECT demonstrates the typical appearance of toxic megacolon on plain film. Note the diffuse colonic dilatation with marked thumbprinting image.
image
Anteroposterior radiograph of supine abdomen demonstrates marked dilatation of transverse colon with a scalloped contour image indicating edematous mucosa.
image
Anteroposterior radiograph of transverse colon in a patient with ulcerative colitis shows a variant appearance of toxic megacolon. The colon is ahaustral but without pseudopolyps typically seen in toxic megacolon.
image
Supine radiograph shows diffusely dilated bowel in an acutely ill patient with ulcerative colitis. The transverse colon is dilated and ahaustral with an irregular mucosal surface.

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