Small bowel imaging changes Crohn's disease algorithms
Advances in small bowel imaging over the past decade have transformed the diagnosis and management of inflammatory bowel disease. New modalities such as CT and MR enterography, CT and MR enteroclysis, capsule endoscopy (CE), and balloon-assisted endoscopy (BAE) have become essential for evaluating the extent and severity of Crohn's disease (CD) and monitoring intestinal response to treatment.
At Mayo Clinic's campus in Rochester, Minnesota, ileocolonoscopy remains the initial diagnostic test of choice, but gastroenterologist David H. Bruining, M.D., says it is now routinely combined with MR or CT enterography.
"Cross-sectional imaging provides us with an objective way of assessing areas we're not otherwise able to interrogate. It doesn't replace endoscopy but rather complements it, giving us a full picture of the disease. Imaging studies outperform traditional barium techniques — and capsule endoscopy — because they have the ability to detect penetrating complications and extraluminal manifestations such as fistula, phlegmon and abscess," he points out.
CT versus MR enterography
CT and MR enterography both use high-volume, orally administered neutral enteric contrast and intravenous contrast to provide detailed visualization of the small bowel wall and lumen. Both also have roughly the same sensitivity for Crohn's-associated inflammation — about 80 to 90 percent. Despite the similarities, certain variables must be taken into account when selecting the most appropriate test for each patient, including availability, clinical effectiveness, safety and cost.
Of the two tests, CT enterography is usually the first test performed for suspected CD in adults. It is more readily available, has a shorter image acquisition time, provides slightly better image quality and costs less than MR enterography.
Although the radiation dose associated with CT enterography can be minimized with the use of automatic exposure control, MR enterography is preferred for younger patients who are likely to undergo multiple lifetime scans, as a follow-up for asymptomatic adults, and when there is the possibility of low-grade obstruction or contraindications for CT, including pregnancy and contrast allergy.
CT and MR enteroclysis
CT enteroclysis and MR enteroclysis use enteric contrast delivered via a nasojejunal tube, which provides superior bowel distention. But because the tests are longer, invasive and less well-tolerated by patients, they are usually reserved for cases of suspected low-grade small bowel obstruction not found by routine imaging.
Jonathan A. Leighton, M.D., a gastroenterologist at Mayo Clinic's campus in Phoenix, Arizona, agrees that many physicians prefer cross-sectional imaging but argues that a role exists for capsule endoscopy because "cross-sectional imaging isn't as exquisitely sensitive at picking up mucosal inflammation as CE. If you want to get a very good look at the bowel mucosa directly and aren't worried about capsule retention, then capsule endoscopy is a good way to do that."
He points to a multicenter study (abstract submitted to United European Gastroenterology Week 2014) comparing ileocolonoscopy with capsule endoscopy in a cohort of 66 CD patients presenting with signs and symptoms of active disease. Capsule endoscopy proved to be as effective as ileocolonoscopy at identifying active disease in the colon and terminal ileum and additionally identified 30 patients (46 percent) with active small bowel Crohn's disease.
Another study, in the April 2014 issue of Clinical Gastroenterology and Hepatology, found that CE had nearly twice the diagnostic yield of small bowel follow-through and was equivalent to ileocolonoscopy for detection of inflammatory lesions.
Dr. Leighton and colleagues are currently recruiting patients for a multi-center study comparing the accuracy of CE with validated scoring systems for assessing mucosal inflammation in patients with known ileal Crohn's disease. "I think capsule endoscopy will continue to be an exciting technology and one to look to for the future," he says.
Unlike conventional enteroscopy, which stretches and lengthens the bowel as the endoscope advances, BAE uses a push-and-pull method that shortens the intestine by pleating the small bowel onto an overtube. The procedure is used to evaluate negative findings of CE in cases of obscure gastrointestinal bleeding and, because it allows for therapeutic interventions, is sometimes used to obtain tissue confirmation before aggressive escalation of therapy. Limitations of the procedure include prolonged duration, the need for greater sedation, and complications such as pancreatitis and perforation.
"Although BAE is useful for evaluating for obscure gastrointestinal bleeding, capsule endoscopy and cross-sectional imaging are used more often because they're less invasive," Dr. Leighton says. "And enteroscopy can be particularly challenging in surgical patients with scarring because you need a mobile small bowel to advance the endoscope."
Several emerging technologies may eventually prove useful for assessing IBD, especially transabdominal ultrasound, which is already widely used in Europe
"Ultrasound is well-tolerated, noninvasive, low cost, and there is no exposure to ionizing radiation," Dr. Bruining says. "We have started our ultrasound program and are exploring how best to optimize the images. In Europe, it is a first line therapy in some centers, but we may use MR or CT enterography at baseline and turn to ultrasound for follow-up, especially in pediatric patients. We are still looking at how it can best be used."
Another imaging technology with limited potential for IBD evaluation is positron emission tomography (PET), which uses radioactively labeled glucose to highlight areas of active inflammation. "PET may be very sensitive, but the cost is currently prohibitive and it increases radiation exposure when performed as PET-CT," Dr. Bruining notes.
Despite these advances, established technologies such as CT and MR enterography are already changing Crohn's disease diagnostic and management algorithms.
"We have all the available options for state-of-the-art small bowel imaging," Dr. Bruining says. "Cross-sectional imaging can provide objective measures of disease activity and extraluminal complications. It can also be used to monitor response to therapy because it has become clear that the correlation between symptoms and disease activity is quite poor and that patients may need to be monitored on the basis of radiographic or endoscopic imaging instead of symptoms."
Dr. Leighton emphasizes that although the perfect timing for the use of various tests isn't always known, they all complement more traditional small bowel modalities.
For more information
Leighton JA, et al. Capsule endoscopy is superior to small-bowel follow-through and equivalent to ileocolonoscopy in suspected Crohn's disease. Clinical Gastroenterology and Hepatology. 2014;12:609.
Mayo Clinic. Monitoring Disease Activity Using Video Capsule Endoscopy (VCE) in Crohn's Disease (CD) Subjects Receiving an Immunomodulator (IMM) and\or a Biological Treatment. ClinicalTrials.gov