Published in UAB Insight, Summer 2008
Noninvasive Imaging of the Small Bowel
Computed tomographic enterography (CTE) is fast becoming the preferred technique for assessment of many small bowel diseases. It is an accurate, noninvasive means to diagnose and assess activity and extent of disease. CTE combines the exquisite spatial and temporal resolution of multidetector-row computed tomography with an ingested low-density contrast agent for visualization of the small bowel. "Conventional small bowel follow-through [SBFT] and endoscopy have limitations," says UAB radiologist Cheri L. Canon, MD. The small bowel is difficult to reach endoscopically because of its length and complex to evaluate fluoroscopically because of the overlapping loops.
CTE is well suited for the evaluation of Crohn disease, small bowel tumors, and occult gastrointestinal (GI) bleeding. CTE findings of Crohn disease include mural hyperenhancement and stratification, bowel wall thickening, adjacent mesenteric inflammation, and fibrofatty proliferation. Hyperenhancement is considered the most sensitive finding, indicating active disease. CTE also allows examination of deep ileal loops and reveals fistula formation, obstruction, and engorged vasa recta (comb sign). A further advantage is that it provides a global evaluation of the entire abdomen and pelvis.
"We use a water-density enteric contrast agent called VoLumen that promotes luminal distention for visualization of mural enhancement and thickening," says Canon. The addition of an intravenous contrast material maximizes the conspicuity of hypervascular abnormalities such as inflamed bowel loops or masses. "In most cases we scan twice - during an early arterial phase and in a later portal venous phase after intravenous contrast injection," Canon says. In several studies, CTE has depicted Crohn disease more accurately than SBFT (Radiology. 2006;238[1]:128-134) and (RadioGraphics. 2006;26[3]:641-662).
Small bowel tumors represent a relatively rare subset of small bowel disease, but CTE accurately identifies carcinoid tumors, adenocarcinoma, lymphoma, GI stromal tumor, and Meckel's diverticulum.
GI Bleeding
Multiphase CTE helps define the etiology of GI bleeding and most common vascular ectasias such as arteriovenous malformations. Traditionally, when upper GI endoscopy and colonoscopy are negative, radiologists use barium fluoroscopy to visualize the small bowel, but that has a very low yield. "When we find no tumor, we presume the bleeding is secondary to vascular malformations in the bowel wall - a diagnosis of exclusion," Canon says. "However, with multiphase CTE we can diagnose vascular malformations in addition to tumors."
"CTE should supersede SBFT in most cases," says radiologist Lincoln L. Berland, MD, chief of CT. "With CTE, we can identify subtleties specific to small bowel diseases and be confident that we have not missed anything."
CTE is not appropriate in some clinical settings. SBFT provides higher-resolution images for mucosal abnormalities in early Crohn disease. Vague abdominal pain and bloating do not warrant a shift from traditional approaches, Canon says. "These are low yield clinical indications, and patients do incur increased radiation dose with CTE when compared to conventional CT."
FOR MORE INFORMATION:
Dr. Cheri Canon
Dr. Lincoln Berland
1.800.UAB.MIST
mist@uabmc.edu