Radiologic testing in Crohn's disease

Answer: The diagnosis of CD is usually the result of a constellation of clinical, endoscopic, radiological, and histological findings. CD, a systemic, segmental chronic granulomatous disease affects the terminal ileum and proximal colon in 70% of cases, small bowel alone in 30%–40%, and isolated colonic disease in 20%.1 Radiological studies are important in making the diagnosis of CD, assessing the extent and severity of disease, and defining the response to medical and surgical therapy. The ideal imaging technique should be one that is cheap, readily available, and highly accurate. Traditionally, small bowel follow-through (SBFT) and small bowel enteroclysis have met this criteria and have been the diagnostic tools of choice for small bowel CD.2,3 Although there is controversy as to which technique is superior, local expertise usually determines which of these modalities is preferred. The SBFT requires ingestion of a barium meal, whereas an enteroclysis requires placement of a nasoduodenal tube through which barium and air are passed. The earliest CD lesions detectable on a barium x-ray are aphthous ulcers. In more advanced CD, the ulcers enlarge and coalesce to form stellate, serpiginous, or deep linear ulcers that appear as cobblestoning on barium x-rays. In penetrating CD the deep ulcers form fissures, sinus tracks, and fistulas; these are readily identified by pooling or tracking of barium transmurally. Chronic inflammatory CD results in intramural fibrosis and scarring that is depicted by circumferential thickening of the bowel wall and significant luminal narrowing. Patients with obstructive symptoms often develop bowel dilation proximal to the stricture that connotes a degree of chronicity and “fixed” fibrostenosis. Often luminal narrowing from inflammatory stenosis and fibrostenotic stricture may be difficult to delineate on barium studies. The treatment implications are important, as patients with obstructing fibrotic strictures require surgery, whereas patients with inflammatory stenosis may respond to medications and have return of normal caliber lumen after treatment.2,4–6 Computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US) are the preferred modalities for evaluating extraluminal CD, e.g., abscesses or phlegmon. The most common finding on CT in CD patients is mural thickening, often associated with perienteric inflammatory stranding.6,7 CT scan is the modality of choice for diagnosing and treating intraabdominal abscesses. Many abscesses detected on CT are amenable to percutaneous drainage. This allows for elective definitive medical or surgical therapy and often avoids the need for emergent surgery and ileostomy. Endoscopic ultrasound (EUS) and pelvic MRI have been particularly useful in diagnosing perirectal and perianal fistula and guiding therapy.8,9 EUS is over 90% accurate in identifying perianal fistula and abscesses. Combined with MRI and surgical exam under anesthesia the diagnostic accuracy rates approach 100%. EUS and MRI may delineate which fistula are simple and complex, and which fistula require surgical intervention alone or in combination with medical therapy. Likewise, EUS and MRI may guide infliximab therapy by determining which fistula are completely healed and which persist despite the external skin portion closing. Video capsule endoscopy (CE) is a useful tool in assessing small bowel CD.10 The role of CE in CD has yet to be firmly established. The CE is more sensitive than barium studies at detecting small mucosal defects that may be of little clinical significance.11 It has been our experience that CE may be a useful study in patients with a known diagnosis of CD and persistent symptoms despite normal SBFT. For example, we have detected significant small bowel CD, i.e., inflammatory stenosis, deep ulcers, stricture, in patients with normal SBFT. This finding has led to alteration in treatment and in a few cases surgery. Also, CE may play a role in patients with indeterminant colitis (IC) scheduled for surgery. Patients with IC and small bowel disease on CE should have a permanent ileostomy rather than ileal pouch anal anastomosis. A combination of CT scan with SBFT affords simultaneous evaluation for intraand extraluminal CD while assessing the abdominal viscera. The recent advent of CT enterography and CT enteroclysis has married these modalities in 1 exam.12,13 The patient is administered oral and IV contrast dye simultaneously. The downside to this combined modality From the Inflammatory Bowel Disease Center, Division of Gastroenterology, Hepatology, & Nutrition, University of Pittsburg School of Medicine, Pennsylvania, USA. Copyright © 2008 Crohn’s & Colitis Foundation of America, Inc. DOI 10.1002/ibd.20614 Published online in Wiley InterScience (www.interscience.wiley.com).