A 27-year-old man presented to the emergency department with lower abdominal pain that had started six hours earlier. He reported nausea and several episodes where he almost vomited. He had vague tenderness in the right lower quadrant of the abdomen, but there was no definitive guarding. You suspect early appendicitis, and are now obligated to obtain imaging before the on-call surgeon will see him.
Abdominal pain is currently the most common presenting complaint to emergency departments in the United States, according to the Centers for Disease Control and Prevention. (Dec. 12, 2017; http://bit.ly/2DpyGrv.) Given that myriad causes of this pain can range from benign to life-threatening, emergency physicians must occasionally order imaging studies to discover the diagnosis.
Oral contrast is routinely used for abdominal CT scans because its presence in the bowel lumen is thought to increase diagnostic accuracy. But recent studies show that requiring a patient to ingest oral contrast can increase his emergency department length of stay anywhere from 30 minutes to two hours. (Emerg Radiol 2010;17:267 and 2012;19:513; West J Emerg Med 2012;13:383; Am J Emerg Med 2012;30:1765.) The first thing we should ask is if administering oral contrast adds anything to our emergency department workup.
Newer-generation multidetector CT scanners significantly reduce scanning time, leading to reduced motion artifact and presumably improved image quality and calling into question the utility of oral contrast. (AJR Am J Roentgenol 2009;193:1282.) A systematic review of 23 articles on appendicitis demonstrated that forgoing oral contrast had no effect on the accuracy of a diagnosis. (Am J Surg 2005;190:474.)
One author examining CT scans ordered for possible appendicitis found that oral contrast reached the terminal ileum in only 72 percent of patients, missing the target organ in more than a quarter of the subjects. (J Surg Res 2011;170:100.) Even then, CT scans ordered with oral contrast proved no more accurate than CT scans without in this single-center study. If oral contrast does not aid in diagnosing infectious or inflammatory conditions, then we should ask if the contrast assists in detecting lumenal injury.
Oral contrast has been advocated as a way to specifically diagnose bowel wall or mesenteric injury for patients presenting with abdominal trauma. This belief has also been challenged, however. A systematic review of 32 articles on the subject of blunt abdominal trauma found that oral contrast administration did not improve diagnostic accuracy compared with no contrast or even PO water intake. (Eur Radiol 2013;23:2513.)
The results are not as clear in penetrating trauma, however, because IV-only contrast CTs have not been compared directly against IV and oral contrast CTs. When IV-only studies are compared with laparotomy, their positive and negative predictive values are 93 percent and 92 percent, respectively. (J Trauma 2009;67:583.) Oral contrast may add only marginal benefit when evaluating trauma patients, so we must finally ask if a radiologist needs it when intra-abdominal fat is lacking.
Some hospitals have eliminated the need for routine use of oral contrast when ordering abdominal CT scans, but certain exceptions apply. A facility might enforce arbitrary cutoffs of body mass index with the theoretical idea that lack of visceral fat impedes diagnosis of inflammatory conditions. This conclusion is not supported by the literature. Regardless of body habitus, radiologists are able to diagnose conditions regardless of intra-abdominal fat content. (Emerg Radiol 2010;17:445, Am J Emerg Med 2006;24:144.) Of note, none of these addresses pediatric patients. Oral contrast may be required by your institution for children regardless of BMI.
Oral contrast is also sometimes required for diagnosing small bowel obstruction, specifically in locating the transition point. Contrast has been shown to help predict the need for surgery (Am J Surg 2016;211:1114), but diagnosis alone can be made on an unenhanced study. (Eur J Radiol 2009;71:135.) The only times in which oral contrast can be routinely recommended are when patients have undergone bowel-altering surgery (e.g., gastric bypass) or when scans are ordered with a specific indication for bowel obstruction. Otherwise, skipping oral contrast in most instances of abdominal CT scan appears prudent.
The diagnostic workup for the patient at the beginning of this article would be aided by CT imaging. Oral contrast would not add further information in diagnosing inflammatory causes of abdominal pain such as appendicitis. The right decision is to order a CT scan with intravenous contrast only so that you can quickly and appropriately disposition the patient.
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