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August 25, 2014

Why I Use Oral Contrast for Abdominopelvic CT Imaging

Many articles have been written in the past several years that have evaluated the elimination of routine oral contrast administration prior to CT imaging for emergency department patients presenting with non-traumatic abdominal pain. 

While the studies vary in protocol and results; the overall consensus finding is that in selected patients the performance of abdominopelvic CT with IV contrast, but without oral contrast, significantly reduces patient length of stay without resulting in a significant increase in missed diagnosis or repeat examinations.

In these studies, certain subsets of patients continued to receive oral contrast, including those patients with inflammatory bowel disease, lean body habitus, recent abdominal surgery, a history of prior gastrointestinal tract-altering surgery, and those unable to receive IV contrast. 

In speaking with my colleagues working at other facilities, I have learned that a few centers have extrapolated these results to the point that they have eliminated the use of oral contrast for virtually all patients undergoing CT, including inpatients and scheduled outpatients, except for certain indications that are similar to those previously listed.  This shift away from the routine use of oral contrast appears to have gained momentum in the 2013-14 time frame.

Personally, I am a strong believer in the benefits of properly administered oral contrast for CT imaging.  I believe that oral contrast both accentuates bowel pathology if it exists and helps to exclude pathology if it doesn’t exist.  Non-distended, non-opacified loops of bowel may hide pathology that is present or may suggest a pathology that is not present. 

The most convincing analogy I can think of is the benefits we receive from the use of IV contrast.  We have a growing number of patients who receive abdominopelvic CT without IV contrast, either because of renal insufficiency or because of the indication for the examination (e.g., renal colic CT).  We can still find plenty of pathology in these patients, such as liver masses and renal masses, but we must make the extra effort to look carefully and adjust our window/level settings. 

The administration of IV contrast in these same patients would make the detection of such pathology much easier because the pathologic process is accentuated against the background of the normal contrast-enhanced organ/structure.  Some of my colleagues place a caveat into the report of each of their non-IV contrast examinations that goes something like this: “The examination is limited by the lack of IV contrast, especially for evaluation of the solid organs.”  

Admittedly, there are some lesions that cannot be detected at all, or if detected,cannot be further characterized without the use of IV contrast.  But many lesions can be seen without IV contrast; it is simply that they are harder to see.  I believe the same holds true for oral contrast. 

With oral contrast present I can see bowel pathology, or pathology adjacent to bowel loops, more easily and I feel more confident in stating that a normal-appearing, well-opacified, well-distended bowel loop is truly normal than if the same loop was non-opacified and non-distended.

When I first started reading abdominopelvic CT examinations in 1990 it was not that difficult to keep up with patients as they were scanned.  Each patient had a series of 10 mm axial slices filmed in soft tissue “windows” with an additional subset of images in lung “windows”.  Scanners were slow and images had to be processed and filmed. 

Fast forward to today and I find myself faced with 5 mm slices in axial, coronal, and sagittal planes.  Each plane can be viewed in multiple window/level settings.  A CT scan can be performed, processed and sent for viewing in less time than it takes me to read the scan. 

Multiply this by multiple CT scanners per facility, some of them in service around the clock, and you can easily see why many of my friends confide in me that they are reading CT scans so quickly, in order to keep up, that they are in constant concern that they will miss something of significance. 

I have the same concerns in my own practice.  Anything that helps me to see pathology or exclude pathology more easily is a definite “must have” for me and I believe oral contrast fits that description. 

Some of the current oral contrast mixing agents are quite palatable, have few side effects, and require only 70-75 minutes of administration time to provide opacification of the bowel from the stomach to the mid ascending colon, which are the areas I believe most benefit from oral contrast. 

I can understand that for emergency departments under significant pressure to move patients through the system quickly, the time savings from avoiding oral contrast may outweigh any perceived benefits in image interpretation, especially when studies suggest that very few patients will return to their facility for treatment of missed pathology. However, I believe that oral contrast administration should still routinely be performed. 

Otherwise, one day I may have to start adding the caveat: “The examination is limited by the lack of oral contrast, especially for evaluation of the GI tract.”

 

Peter Quagliano, M.D.
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