eMedicine Specialties > Radiology > Gastrointestinal

Colitis, Pseudomembranous: Imaging

Author: Vinay K Gheyi, MD, MBBS, Chief of Radiology, Department of Radiology, McGuire VA Medical Center, Richmond, Virginia
Coauthor(s): John S Wills, MD, Associate Professor of Radiology, Thomas Jefferson University; Chair, Department of Radiology, Pennsylvania Hospital; Raul N Uppot, MD, Instructor in Radiology, Harvard Medical School;, Assistant Radiologist, Department of Radiology, Section of Abdominal Imaging and Interventional Radiology, Massachusetts General Hospital
Contributor Information and Disclosures

Updated: Sep 19, 2007

Radiography

Findings

Plain films of the abdomen are notoriously insensitive for diagnosis of PMC. The findings may range from normal to nonspecific, but as plain films are often the first studies to be ordered, it is important to be aware of these findings. Classic findings consist of the following:

1. Colonic dilatation — Findings range from colonic ileus to toxic megacolon and even perforation with pneumoperitoneum. Toxic megacolon is suggested by acute dilatation of transverse colon to a diameter greater than 6 cm associated with systemic toxicity and the absence of mechanical obstruction.
2. Nodular haustral thickening (see Image 3) — This is considered to be fairly specific for PMC but is observed only in severe cases.¹ Any part of the colon may be involved. In a study by Boland et al, the transverse colon was most commonly involved, followed by the left colon and then the right colon.⁵  
3. Thumb printing — This is nonspecific, since it can be observed with either inflammatory or ischemic colitis.

Barium enema

Contrast enemas should be avoided in patients with possible PMC because of potential risk for perforation. Barium enemas are rarely indicated, especially with the advent of cross-sectional imaging.

Barium enema findings may vary, depending on the severity of the disease. In the milder forms, nodular filling defects involving the mucosa may be observed that coalesce as the disease progresses, giving an irregular appearance to the bowel wall (see Image 4). The serrated outline of the colon does not result from mucosal ulceration but, rather, is a consequence of trapped barium between the plaquelike membranes.

Degree of Confidence

Plain radiographic abnormalities may be observed in only 32% of cases of PMC.⁵

False Positives/Negatives

Plain film findings may suggest a diagnosis of PMC but usually are insensitive. Even if the radiographs demonstrate abnormalities, they tend to underestimate the extent and severity of the disease.⁴

Computed Tomography

Findings

With increased use of CT as a primary imaging modality in the evaluation of patients with diffuse abdominal pain or fever, it is critical for radiologists to recognize CT features of PMC.¹ CT findings, although not specific, may be highly suggestive of PMC, and CT is excellent for evaluation of the extent of PMC (Ros, 1996).¹

The following are CT findings in PMC:

1. Marked colonic wall thickening (see Image 5). Colonic wall thickening is the most common CT finding in patients with PMC and ranges from 3-32 mm.⁴ Most cases reveal total colonic involvement; however, focal and segmental involvement has been well documented. Mural thickening can be smooth or irregular and eccentric or concentric. PMC more often causes irregular and shaggy wall thickening rather than the smooth and homogeneous thickening observed with Crohn disease.⁴
2. Target sign — On contrast-enhanced CT, mucosal hyperemia leads to enhancement with relatively hypodense submucosa secondary to edematous changes. This gives the appearance of a bull's eye or target sign. The sign is better appreciated on the arterial phase of enhancement. It is a nonspecific sign and has been reported with other forms of colitis such as Crohn disease and ulcerative colitis.
3. Accordion sign — This is highly suggestive of PMC but is only observed in advanced disease. The cause of this sign is entrapment of orally administered barium in between thick and edematous haustral folds, giving alternating low- and high-density bands (see Image 6).
4. Pericolonic stranding — If observed, this is usually mild, reflecting mucosal rather than serosal involvement. The typical CT appearance of PMC is mild pericolonic stranding disproportionate to marked colonic wall thickening.
5. Ascites — This is a nonspecific finding and tends to occur in severe cases of PMC. Ascites is observed on CT in an average of 35% of patients.¹
6. Other findings — Pneumatosis, toxic megacolon, and portal venous gas may be observed. These features are nonspecific and may be observed with severe colitis of any cause.

Degree of Confidence

The sensitivity of detection of PMC on CT is approximately 85%. Specificity of CT is low (approximately 48%), since other types of colitis can cause a similar appearance.⁶

Ultrasonography

Findings

Ultrasound is not commonly used for evaluation of possible PMC; however, it may be helpful in evaluation of postoperative patients in surgical intensive care units who are on antibiotics and develop nonspecific abdominal symptoms.¹ Thickened colon may be discovered incidentally during ultrasound examination of the abdomen.

Ultrasound findings rely on wall thickening of the colon, as well as the target sign, demonstrated by hyperechoic mucosa in the background of hypoechoic edematous submucosa. Ascites may be an associated finding and has been observed in as many as 77% of cases.⁷

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