Pros and cons of imaging modalities for pediatric IBD
Inflammatory bowel disease (IBD) is one of the most serious gastrointestinal diseases affecting children in the Western world. It has a complex and variable course, and diagnosis not only includes endoscopy but also small bowel imaging to assess mucosal alterations and transmural involvement as well as response to treatment. As a result, patients are likely to have multiple imaging studies over a lifetime.
No consensus exists about the best imaging modality for pediatric IBD. Providers must balance diagnostic accuracy against exposure to ionizing radiation and account for a child's age, maturity level and tolerance of a particular technique.
Jeanne Tung, M.D., a gastroenterologist specializing in the evaluation of children with IBD at Mayo Clinic's campus in Minnesota, recommends small bowel follow-through (SBFT) for children younger than 10.
"Most young children aren't capable of being in a room by themselves with a big, scary machine," she says. "With small bowel follow-through, they are in the presence of a provider and a reassuring parent for the duration of the study. There is some radiation exposure — in the pediatric population, the effective dose is about 1.2 to 1.5 millisieverts."
SBFT images show less mucosal detail than do other modalities and don't detect extraluminal complications, so cross-sectional imaging with CT or MRI is usually recommended for older children and teens. Both CT enterography (CTE) and MR enterography (MRE) have similarly high sensitivity and specificity. Both also show pathologic changes in the bowel wall and detailed information about the extent, severity and distribution of disease as well as provide extraintestinal information such as mesenteric fat stranding, primary sclerosing cholangitis of the liver, autoimmune pancreatitis and bone changes.
CT vs. MR enterography
Both modalities also have drawbacks. CTE exposes children to ionizing radiation — about 3.1 millisieverts for one abdominal scan. Although the dose can be individualized based on size, children with IBD, especially Crohn's disease, may experience significant cumulative radiation exposure from CT studies. Because of the potential increased risk of malignancy associated with radiation exposure, Mayo Clinic began offering MRE for pediatric patients in 2007.
In the September 2012 issue of the American Journal of Roentgenology, Mayo Clinic researchers published the largest North American study of MRE in pediatric patients with IBD. A retrospective analysis of 85 studies in 70 patients — more than half with Crohn's disease — confirmed that the procedure could be successfully completed in children age 9 and older. Most children were able to consume one bottle of contrast material and only three experienced self-limiting side effects — findings similar to those in adults.
The quality of both unenhanced and contrast-enhanced image was acceptable, and the sensitivity of MRE for active disease, as defined by reference colonoscopy, was 80 percent for the terminal ilium, 79 percent for the right colon and 90 percent for the left colon.
In patients who may have a perianal fistula, an MR pelvis is the preferred modality. Still, MRE has lower spatial resolution and longer acquisition time than CTE, is more expensive and is less readily available in some institutions. It also requires that young patients lie still in a confined space for up to 45 minutes.
"We try to encourage MRE if patients can tolerate it, but some children who have had a negative experience are reluctant to show up for repeat endoscopies and enterographies. I have a frank discussion with patients, asking whether they can tolerate being in a machine for 45 minutes versus 15 minutes," Dr. Tung says. "Anecdotally, we find that patients who experienced cramping and nausea during MRE usually had active disease and were able to tolerate the test better when they were in remission."
Some children can't tolerate either CTE or MRE because of the contrast. In that case, one option is to perform the small bowel follow-through. Another alternative is to consider switching to a more palatable contrast material.
Making the test experience as stress-free and child friendly as possible helps, too. "We like to involve a child life specialist, who can teach patients relaxation techniques and explain the procedure in a safe and nonthreatening way. We also have dedicated pediatric radiologists who know how to work with children. We recommend using technology, if possible — headphones with music and videos for kids to watch. We want to make the test as pleasant and nonthreatening as possible because we're going to have to repeat it sometime down the road," Dr. Tung says.
For more information
Absah I, et al. MR enterography in pediatric inflammatory bowel disease: Restrospective assessment of patient tolerance, image quality, and initial performance estimates. American Journal of Roentgenology. 2012;199:W367.