Date Published: December 19, 2017
Publisher: Springer US
Author(s): Alexandra Medellin, Christina Merrill, Stephanie R. Wilson.
Contrast-enhanced ultrasound (CEUS) of the gastrointestinal tract provides vascular information helpful for characterizing masses and other pathologies in and around the bowel, similar to contrast applications in other solid organs. However, the use of microbubble contrast agents for the bowel provides additional unique contributions as it gives both subjective and objective information about mural and mesenteric blood flow, invaluable for the determination of disease activity in those many patients affected by inflammatory bowel disease (IBD). IBD is a lifelong chronic disease and has its peak age of onset in adolescence or young adult life. Today, we have moved away from treating patient’s symptoms and strive instead to alter the course of disease by obtaining mucosal healing. Expensive and aggressive biologic therapies and lack of agreement of patient’s symptoms with their disease activity and complications necessitate frequent imaging surveillance, which must be safe, readily available, inexpensive, and effective. Ultrasound with the benefit of contrast enhancement meets these requirements and is shown in meta-analysis to be equivalent to CT and MRI scans for these indications.
Sonographic evaluation of the bowel begins with identification of abnormal loops and determination of disease extent and location. US features of active disease include bowel wall thickening (> 3 mm for small bowel and > 5 mm for colon), hyperemia detected with CDI , the presence and amount of inflammatory fat and lymphadenopathy . These parameters allow for the selection of the most abnormal segment that can be studied with CEUS. Two important considerations when selecting the bowel segment for evaluation with CEUS include a well-visualized loop of bowel within the field of view with minimal or no peristalsis and bowel wall thickness of > 4 mm. This will ensure the best technical acquisition, especially for quantification. In our experience, loops in the lower quadrants, away from the influence of respiratory excursion, are optimal. In the majority of the cases, this is possible, as IBD most often affects the terminal ileum and the cecum. If an abnormal loop is identified with significant peristalsis, 20 mg IV of hyoscine butylbromide (Buscopan) over 1 min or glucagon 1 mg IV is used to minimize the bowel activity, if there are no contraindications. In our experience, antimotility medications are required in less than 10% of the cases of bowel CEUS.
CEUS may be utilized in evaluation of the bowel providing information about mural and mesenteric blood flow in a wide variety of situations. Similar to the use of intravascular contrast agents for CT and MR enterography, the addition of contrast agents to US will provide valuable information wherever blood flow knowledge would be helpful. However, it is in the evaluation of the population with IBD where the addition of CEUS has had its greatest clinical impact, substantially improving the role of ultrasound in the evaluation of the bowel. Although CDI is invaluable in bowel assessments, it has shortcomings which are easily overcome with CEUS. In addition, CEUS provides both subjective and objective quantification of mural blood flow. This is particularly important in the young population with IBD that requires frequent imaging surveillance and follow-up throughout the course of this chronic disease. Ultrasound and CEUS provide a non-invasive and accurate assessment of the classic features of CD and are highly sensitive for the detection and diagnosis of complication. In the future, CEUS of the bowel should be regarded as an essential component of standard care for imaging of the bowel in IBD.