The abdominal radiograph is most useful in the setting of acute illness and has little role in the routine evaluation of IBD. The acute abdominal series should include a supine or prone view, an upright or left lateral decubitus view, and an upright chest radiograph whenever possible. In CD, small bowel obstruction (SBO) due to stricture can be identified on abdominal radiographs. SBO is indicated by small bowel dilatation (generally >3 cm), multiple air-fluid levels, and often a decompressed colon (due to the evacuation of luminal contents downstream from the obstruction). In UC, the abdominal radiograph is most useful when toxic megacolon is suspected. This is characterized by dilatation of the colon (averaging 8 to 9 cm), wall thickening/nodularity (reflecting edema), and absence of colonic haustra (2). The previously reported affinity of toxic megacolon for the transverse colon likely reflects the visibility of the air-filled transverse colon on supine radiographs rather than a true predilection for this site (3).

In the past, SBFT was the mainstay for evaluation of small bowel involvement in IBD. This is changing with the advent of advanced CT and MRI techniques. However, SBFT will remain a useful technique, as it provides the greatest spatial resolution and the ability to manipulate the bowel using a combination of compression and patient positioning. A combined upper gastrointestinal (UGI) examination of the esophagus and stomach with the SBFT (UGI/SBFT) is generally not necessary unless the patient has symptoms localizable to the upper tract; upper GI involvement by CD is much less common than small bowel involvement, and the combined exam involves more radiation to the patient. A dedicated SBFT is often better suited for patients where small bowel disease is the major focus.

For the SBFT exam, the patient is administered barium sulfate suspension by mouth, after which the progress of the “contrast column” through the small bowel is monitored using serial abdominal radiographs. After the contrast column has reached the cecum (or earlier if abnormal bowel is detected on the serial abdominal images), real-time fluoroscopy is performed with specific emphasis on the terminal ileum. If the terminal ileum cannot be adequately imaged using the singlecontrast (barium only) technique, pneumocolon can be performed to provide double contrast (air and barium). This technique, which involves air-insufflation through a flexible tube placed in the rectum, provides the most detailed view of the terminal ileum mucosa and therefore has the greatest sensitivity in early or mild IBD involvement (4).

Conventional enteroclysis allows a more detailed evaluation of the entire small bowel, but has the drawbacks of requiring preprocedural cathartic colon cleansing, nasojejunal intubation, and increased radiation to both the patient and the radiologist performing the exam. An enteric tube is placed from the nose to the proximal jejunum using fluoroscopic guidance. An occlusion balloon at the end of the tube is inflated and barium suspension is administered using a pump mechanism. The leading edge of the contrast column is followed using intermittent fluoroscopy, with real-time abdominal compression and spot images acquired when an abnormality is detected (5).

Early active inflammatory CD on barium fluoroscopic examination is characterized by thickening or mild nodularity of the mucosa resulting from edema or lymphoid proliferation (3). Shallow erosions surrounded by a circle of edema can also result, representing aphthous ulcers (Fig. 3.1). With intermediate active inflammatory CD, the edema and nodularity of the mucosa progresses, causing fold distortion or obliteration. The aphthous ulcers may increase in depth and width, often fusing to produce crescentic or linear tracks in the mucosa. The increased inflammation can result in thickening and sclerosis of the involved mesentery, producing retraction on the mesenteric border of the affected small bowel. The redundancy created on the antimesenteric border often results in sacculations that are probably the most striking radiologic manifestation of the “asymmetric” bowel involvement in CD (Fig. 3.2). Advanced active inflammatory disease involves the full thickness of the bowel wall, and the imaging characteristics reflect this feature. Deep linear fissures, often in a crosswise pattern of axial and transverse clefts, leave islands of preserved yet edematous mucosa. This results in the so-called ulceronodular or “cobblestone” appearance (Fig 3.3A). The lumen of the bowel is narrowed and the diseased bowel loops appear separated from adjacent loops. This bowel separation is secondary evidence of the bowel wall thickening and perienteric fibrofatty proliferation seen in advanced CD. When the lumen of the bowel is sufficiently narrowed, threadlike contrast filling of the remaining lumen produces the so-called “string sign” of CD.

The fibrostenotic subtype of CD results when collagen deposition in the small bowel produces strictures. These strictures are a common cause of SBO in CD
patients and often necessitate surgery. On barium fluoroscopic exams, strictures will appear as fixed and aperistaltic narrowing in the bowel lumen. When strictures are severe or longstanding, the small bowel just proximal to the stricture will often dilate. Strictures can be multifocal and noncontiguous, reflecting the “skip lesions” of CD, often with dilatation of the intervening small bowel segments. The differentiation of fibrotic from inflammatory stenosis is clinically important, as the former often requires surgery and the latter is generally treated with medication. This diagnostic separation can be quite difficult on fluoroscopic examination, often necessitating follow-up examination after medical therapy to evaluate for lesion response.