Toxic Megacolon Workup

Updated: Mar 01, 2018
  • Author: Brian Lin; Chief Editor: Burt Cagir, MD, FACS  more...
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Approach Considerations

Complete blood count (CBC)

Patients with toxic megacolon (toxic colitis), or TM (TC), may develop leukocytosis with a left shift. Patients can also present with leukemoid reaction. Additionally, bloody diarrhea results in anemia.

Although the presence of an increased white blood cell count contributes to the diagnosis of TM (TC)—and most investigators believe that the absence of a high white blood cell count makes defining a disease as toxic megacolon difficult—an abnormally low count, or even a white blood cell count that is within normal limits, does not rule out toxic megacolon. This is because in immunosuppressed or extremely toxic patients, the white blood cell count actually may be normal or low.

Chemistry panel

Electrolyte disturbances are very common in TM (TC) secondary to inflammatory diarrhea, steroid use, and ongoing gastrointestinal losses. The inflamed colon is unable to reabsorb salt and water.

Nutrition and coagulation panel

A coagulation panel should be ordered in the event that surgery is required. A nutrition panel, in accordance with the physician's practice, is helpful in determining treatment (eg, albumin vs prealbumin) and in assessing nutritional status.


Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels are usually elevated. Although these findings may support the diagnosis of TM (TC), they are not specific.


Pathology in cases of TM (TC) demonstrates acute inflammation involving all layers of the colon. Variable amounts of necrosis and degeneration are present. Infiltration by inflammatory cells (neutrophils, macrophages, and lymphocytes) is noted. The myenteric and submucosal plexuses are usually preserved.



Plain abdominal radiographs are essential for the diagnosis and management of toxic megacolon (toxic colitis), or TM (TC). Repeated abdominal plain films are necessary to evaluate the efficacy and progress of treatment.

Radiographic findings include the following:

  • Dilated (>6 cm) transverse colon (see the image below)

    A 22-year-old man presented with abdominal pain, p A 22-year-old man presented with abdominal pain, passage of blood and mucus per rectum, abdominal distention, fever, and disorientation. Findings from sigmoidoscopy confirmed ulcerative colitis. Abdominal radiographs obtained 2 days apart show mucosal edema and worsening of the distention in the transverse colon. The patient's clinical condition deteriorated over the next 36 hours despite steroid and antibiotic therapy, and the patient had to undergo a total colectomy and ileostomy.
  • Loss of colonic haustrations, possible "thumbprinting" (see the image below)

    Plain abdominal radiograph from a patient with kno Plain abdominal radiograph from a patient with known ulcerative colitis who presented with an acute exacerbation of his symptoms. This image shows thumbprinting in the region of the splenic flexure of the colon.
  • Presence of intraluminal soft-tissue masses (ie, pseudopolyps)

  • Free intraperitoneal air - Possible finding, best seen on upright chest radiograph or left lateral decubitus abdominal film

  • Segmental parietal thinning as pathognomic for toxic megacolon [4]

Comparison with old baseline films, if these are available, is helpful. Avoid barium studies in a patient who is severely toxic; the potential for perforation is considerable.



Maconi et al found intestinal ultrasonography potentially to be a diagnostic test for toxic megacolon. [29] The investigators demonstrated similar findings in 4 cases. The findings, including the following, need further evaluation by more studies:

  • Complete loss of haustra coli of the colon

  • Hypoechoic and thickened bowel walls with irregular internal margins in the sigmoid and descending colon

  • Marked dilation of the transverse colon (>6 cm), a finding that correlated well with the plain radiograph of the abdomen

  • Hypoechoic and thin (< 2 mm) bowel walls without haustra coli in the dilated colon; in patients who underwent surgery, the postoperative pathohistologic findings of the bowel walls correlated with the ultrasonographic features observed before surgery

  • Slight dilation of ileal bowel loops (diameter >18 mm) with increased intraluminal gas and fluid


CT Scanning

A computed tomography (CT) scan should probably be obtained in patients for whom the diagnosis of toxic megacolon (toxic colitis), or TM (TC), is being considered. A CT scan may identify a local or contained perforation.

If the diagnosis remains unclear or the cause of toxicity is thought to be an abscess, a CT scan may be helpful. There is little literature on the role of CT scanning in TM (TC), but additional studies may help to further define the role of this imaging modality in diagnosing and deriving a prognosis for TM (TC). (See the image below.)

Computed tomography scan from a patient with pseud Computed tomography scan from a patient with pseudomembranous colitis demonstrating the classic accordion sign.


If the diagnosis of toxic megacolon (toxic colitis), or TM (TC), is in doubt and the patient's condition is not toxic or unstable, endoscopy may be attempted by appropriately trained personnel.

Endoscopy may take the form of flexible sigmoidoscopy or colonoscopy. If clinical concern of TM (TC) exists, the examination should not progress beyond sigmoidoscopy, if at all. The scope should be advanced only as far as is needed for diagnosis. Air insufflation should be a minimal.

According to some experts, colonoscopy is generally justified only if the patient has no or minimal inflammation of the sigmoid or rectum. Perforation is an obvious potential complication of this approach.