MR enterography feasible for imaging in pediatric IBD
Inflammatory bowel disease (IBD) is a complex disorder with a variable course that may require frequent cross-sectional imaging to assess mucosal alterations, transmural involvement, and abscess and fistula formation as well as response to treatment.
Young IBD patients are especially likely to have multiple imaging studies — not only over a lifetime but also in the short term because of the possibility of extensive silent progression of disease, explains William A. Faubion, M.D., of Mayo Clinic in Minnesota. In children, IBD can profoundly affect growth, weight gain, bone mineralization and onset of puberty.
Until recently, CT enterography was the preferred method for diagnosing and monitoring Crohn's disease in both adults and children. It allows rapid visualization of the bowel wall, shows extraenteric involvement, has a high sensitivity for bowel strictures, and provides detailed information about the extent, distribution and severity of disease.
But recent research shows children with IBD, and particularly Crohn's disease, experience significant cumulative radiation exposure from serial CT studies. Because of the potential increased risk of malignancy associated with radiation exposure and because young IBD patients may already be at higher risk of malignancy from medications and chronic inflammation, Mayo Clinic began using MR enterography for pediatric patients in 2007. "We are deeply concerned about the amount of radiation children and adolescents with Crohn's disease receive, especially since the youngest patients are the most radiosensitive. We don't worry so much about people over 45 — they're relatively radioresistant," Dr. Faubion says.
In general, the one approach at Mayo Clinic is to use MR enterography for patients age 35 and younger who need or have a history of multiple CTs, explains David H. Bruining, M.D., also of Mayo Clinic in Minnesota. He notes, "The advantage for children, teens and young adults is the lack of radiation exposure. For older adults, the advantages are a little less clear, and we perform either CT or MR enterography based on the clinical scenario. CT requires less time in the scanner and there is less interobserver variability."
The advantages of MR enterography for children younger than age 9 are also not clear, both doctors say. Challenges for these patients include poor tolerance for oral contrast as well as the inability to comply with breath-holding directions and remain still throughout the procedure. "We really haven't been able to use the technology in children under 9 because the procedure takes so long, the MRI scanner is confining, the large volume of oral contrast often causes nausea and vomiting, and the whole process can be scary and intimidating," Dr. Faubion explains.
Pediatric MR enterography study
In the September 2012 issue of the American Journal of Roentgenology, Mayo Clinic researchers published the largest North American study of MR enterography in pediatric IBD patients. A retrospective analysis of 85 studies in 70 patients — more than half with Crohn's disease — occurring over 30 months confirmed that the procedure can be successfully completed without sedation in children age 9 and older. Most patients were able to consume one bottle of contrast material and only three experienced self-limiting side effects — findings similar to those in the adult IBD population.
Image quality of both unenhanced and IV contrast-enhanced images was acceptable, and the sensitivity of MR enterography for active disease, as defined by reference colonoscopy, was 80 percent for the terminal ileum, 79.1 percent for the right colon, and 90.3 percent for the left colon. MR enterography also detected 10 cases of small bowel involvement beyond the reach of endoscopy.
Cross-sectional imaging options for children younger than 9 remain more limited. "In a child who is 5, 6 or 7 years old, we might do CT — it's fast, uses an open tube, and children don't have to hold their breath or follow directions," Dr. Faubion says. "We also do small bowel X-rays in young people if they can drink barium. Prior to CT, we did barium studies, and in some patients, that's a reasonable option."
Dr. Bruining points out that MR enterography is not used in other subsets of patients, including those who have cognitive impairments or are extremely ill. "In patients under 35 with multiple CTs, we use MR enterography," he says. "If patients need to get one test, and I need to be confident, I use CT enterography, knowing it's the highest image quality and I can get images quickly."
Because no single imaging technique is the gold standard for all patients or disease manifestations, the search for a fast, inexpensive, well-tolerated, radiation-sparing method for detecting and monitoring bowel disease is ongoing. Transabdominal ultrasound, available in specialized centers in Europe and Canada, is one possibility.
In this procedure, which requires high-frequency, linear-array probes, oral or IV contrast agents may be used to enhance ultrasonography, and clinicians look for some of the same findings they would look for using enterography, such as bowel wall thickening and increased vascularization.
Mayo Clinic has started a transabdominal ultrasound program, scheduled to get underway next year. Dr. Bruining explains, "It's an exciting possibility for pediatric patients and perhaps for adults, but some issues still need to be resolved, such as the need for contrast, accuracy in higher BMI patients and whether the test can pick up disease outside the bowel. Mainly, we want to validate that it's equivalent to other imaging studies. Ultimately, it's about finding the right test for the right patient."
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.