Answer
With increased use of CT as a primary imaging modality for evaluating inflammatory bowel disease (IBD), radiologists must be able to recognize the features of ulcerative colitis on CT. Although barium studies remain the principal tool for diagnosing and evaluating suspected IBD, CT may aid in differentiating ulcerative colitis and Crohn disease when results of barium studies are equivocal. High-resolution thin-section imaging of both the intraluminal and extraluminal components enables radiologists to detect and stage colonic pathology. [17, 18, 19, 20, 21]
CT is valuable for the detection and characterization of ulcerative colitis. CT typically demonstrates circumferential, symmetrical wall thickening with fold enlargement. Thickening of the colon wall (mean, 7.8 mm; standard deviation, 1.9) may be present, with inhomogeneous attenuation, a target appearance of the rectum, and the proliferation of perirectal fat. The normal colonic wall has a maximal thickness of 3 mm with the lumen distended and 5 mm with the lumen collapsed. In comparison, Crohn colitis causes greater bowel wall thickening (mean, 11 mm; standard deviation, 5.1). Such thickening appears in association with homogeneous attenuation, fistula and abscess formation, and mesenteric abnormalities.
The target sign consists of an inner ring of soft tissue attenuation, representing mucosa, lamina propria, and enlarged muscularis mucosa; a middle ring of low attenuation, resulting from widening and fatty infiltration or edema of the submucosa; and an outer area of soft tissue attenuation, representing the muscularis propria. If the submucosa is infiltrated by fat, this is a sign of chronicity; it is more specific to IBD. This sign is best appreciated on the arterial phase of enhancement. It is a nonspecific sign that is also reported in cases of Crohn disease and pseudomembranous colitis.
Ulcerative colitis is typically left sided or diffuse; only rarely does it involve the right colon exclusively. In cases of ulcerative colitis, wall thickening may be diffuse and symmetrical; by contrast, in cases of Crohn disease, wall thickening is eccentric and segmental, and skip lesions are present. The proliferation of perirectal fat is a nonspecific sign that can be seen in any of the colitides. Submucosal fat deposition is present significantly more often in ulcerative colitis (61%) than in Crohn colitis (8%).
Mural thickening of the terminal ileum may be visualized in 10-25% of patients; such thickening is caused by backwash ileitis, which occurs as a result of the reflux of colonic contents into the distal ileum. Abscesses and pseudodiverticula are not features of ulcerative colitis; they occur almost exclusively in Crohn colitis.
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Double-contrast barium enema study shows changes of early disease. Note the granular mucosa.
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Double-contrast barium enema studies show changes of early disease. Note the granular mucosa.
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Double-contrast barium enema studies in a 44-year-old man known to have a long history of ulcerative colitis. Images show total colitis and extensive pseudopolyposis.
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Plain abdominal radiograph in a patient (same as in the previous image) who presented with an acute exacerbation of his symptoms. Image shows thumbprinting in the region of the splenic flexure of the colon.
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Plain abdominal radiograph obtained 2 days later in the same patient as in the previous image shows distention of the transverse colon associated with mucosal edema. The maximum transverse diameter of the transverse colon is 7.5 cm. The patient was treated for toxic megacolon.
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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 total colectomy and ileostomy.
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Plain abdominal radiograph in a patient with known ulcerative colitis who presented with abdominal pain, peritonism, and leukocytosis. At surgery, a perforated toxic megacolon superimposed on ulcerative colitis was confirmed.
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Increased postrectal space is a known feature of ulcerative colitis.
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Plain abdominal radiograph on a patient with known ulcerative colitis who presented with an acute exacerbation of his symptoms. Image shows thumbprinting in the region of the splenic flexure of the colon.
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Double-contrast barium enema study shows pseudopolyposis of the descending colon.
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Single-contrast enema study in a patient (same patient as in the previous image) with known ulcerative colitis in remission shows a benign stricture of the sigmoid colon.
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Plain abdominal radiograph in a 26-year-old with a 10-year history of ulcerative colitis shows a long stricture/spasm of the ascending colon/cecum. Note the pseudopolyposis in the descending colon.
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Single-contrast enema study in a patient with total colitis shows mucosal ulcers with a variety of shapes, including collar-button ulcers, in which undermining of the ulcers occurs, and double-tracking ulcers, in which the ulcers are longitudinally orientated.
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Double-contrast barium enema study shows total colitis. Note the granular mucosa in the cecum/ascending colon and multiple strictures in the transverse and descending colon in a patient with a more than a 20-year history of ulcerative colitis.
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Single-contrast barium enema study shows burnt-out ulcerative colitis.
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Scan obtained with technetium-99m hexamethylpropylamine oxime (HMPAO)–labeled WBCs in a patient with active colitis involving the transverse and descending colon.
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Intravenous urogram shows features of ankylosing spondylitis.
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Lateral radiograph of the lumbar spine shows a bamboo spine.
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Single-contrast barium enema study in a patient with Shigella colitis.
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Postevacuation image obtained after a single-contrast barium enema study shows extensive mucosal ulceration resulting from Shigella colitis.
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Double-contrast barium enema studies show granular mucosa associated with Campylobacter colitis.
