Pushing the boundaries of cross-sectional imaging

Over the last decade, many centers adopted enterography as the standard of care for monitoring the extent and severity of inflammatory bowel disease (IBD). David H. Bruining, M.D., of Mayo Clinic in Minnesota, notes that in 2002, almost all small bowel imaging for IBD at Mayo was barium based. Today, less than 20 percent is.

He attributes enterography's rapid adoption at Mayo to a 2008 prospective comparison of CT enterography (CTE), capsule endoscopy, ileocolonoscopy and small bowel follow-through for the diagnosis of Crohn's disease. The study showed CT enterography was superior to small bowel follow-through and as sensitive as capsule endoscopy. But Dr. Bruining stresses that enterography would not have been as accepted without a collaborative partnership between radiologists and gastroenterologists.

"Endoscopy and enterography are complementary; I don't see one replacing the other," he says. "It's important to have modalities that assess the small bowel beyond the reach of the endoscope. Enterography provides a transmural view of the entire bowel wall, including mural thickness, enhancement and stratification, as well as perienteric inflammatory changes. It's also a valuable modality for detecting penetrating complications and extraintestinal disease manifestation."

He points to a retrospective study of 357 Mayo patients with previously diagnosed Crohn's disease who underwent CTE between 2004 and 2005. Twenty percent had penetrating complications — a new finding in 58.1 percent of those patients. Eighteen percent had extraintestinal disease, a new finding in 67.2 percent.

MR enterography (MRE), which has been studied extensively at Mayo Clinic since 2009, is preferred for perianal imaging, where it can detect abscesses and fistulas.

Planning and assessing therapy

CT or MR enterography is also increasingly used to assess response to therapy, especially when patients don't seem to improve.

One recent study looked at people with Crohn's disease who had serial enterography while undergoing treatment with infliximab (Remicade). Imaging demonstrated intestinal remodeling in two-thirds of patients, even though symptoms did not correlate with the radiologic response.

"It's becoming 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. Bruining explains.

Enterography can also significantly influence therapeutic decision making for patients with IBD. In a recently published study, Dr. Bruining and colleagues prospectively assessed nearly 300 patients with known or suspected Crohn's disease undergoing CT enterography. Providers were asked to complete pre- and post-imaging questionnaires regarding potential management plans along with physician level of confidence for the presence or absence of small bowel disease and complications.

After CT enterography, management plans changed for more than half of patients — 48 percent with established disease and 54 percent with suspected disease, with 24 percent of previously diagnosed patients receiving additional medication. Seventy-eight percent of providers expressed improved level of confidence.

CTE vs. MRE

Despite reduced-dose CT imaging, questions remain about the safety of cumulative exposure to CT radiation, especially for young patients. Dr. Bruining points out that CTscanning is a faster and easier way to acquire images for patients who can't tolerate a longer procedure. "It currently takes a few minutes to perform a CT. The same scan might take 30 to 45 minutes using MRE," he says.

And although some studies have shown that MR and CT images are roughly equivalent — contesting the long-held belief that CTE provides better resolution — cost and availability are still barriers to the use of MRE.

Even so, Mayo physicians try to minimize exposure for all patients, and MRE is the imaging method of choice for children.

Dr. Bruining says the advances in both technologies result from Mayo's interdisciplinary approach to small bowel imaging. "We have a small bowel interest group that meets on a weekly basis," he says, "and we wouldn't have gotten as far as we have without a phenomenal partnership between gastroenterologists and radiologists. Mayo is a unique place that fosters this kind of collaboration; it's what led us to reduced-dose CT imaging and to further develop MR enterography. It keeps us pushing the field forward."

Key members of the small bowel interest group include radiologists Joel G. Fletcher, M.D., Jeff L. Fidler, M.D., James E. Huprich, M.D., and John M. Barlow, M.D..