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Jan 10, 2015

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Enteral contrast for CT diagnosis of appendicitis

Sanjay Arora MD and Michael Menchine MD

Written summary courtesty of EMRAP. Author: Marlowe Majoewski

Drake FT et al. Enteral Contrast in the Computed Tomography Diagno- sis of Appendicitis: Comparative Effectiveness in a Prospective Surgical Cohort. Ann Surg. 2013 Oct 10PMID: 24598250.

Bottom line: This study confirms that the addition of oral and/or rectal contrast does not increase the accuracy of CT scanning in patients with suspected appendicitis.

The Review: Appendicitis is very common with a lifetime risk estimated at 8.6% for men and 6.7% for females. The clinical imperative has been to miss zero cases. The traditional approach has led to acceptance of a high rate of negative appendectomies. CT imaging can reduce the rate of negative appendecto- mies without increasing the rate of perforation. Previously, patients were given oral, rectal, and IV contrast prior to CT scanning. Contrast agents add time, discomfort, and the potential for contrast-related complications. CT technology has advanced.

There have been three trials of IV and oral contrast versus IV contrast alone, which have found similar diagnostic accuracy. Some centers are adopting IV-only protocols.

The Study: The authors looked at a large database of CT scans performed in Washington. The registry captures about 85% of non-elective appendectomies. They collect all imaging and lab data. The data is abstracted and includes 56 hospitals in Washington, which represents nearly all of them.

The outcome of interest in this study was the concordance of radiology imaging and final radiology interpretation. The results were analyzed by the type of contrast used: no contrast, IV contrast, IV and enteral contrast, or enteral contrast only.

9,047 patients underwent appendectomy in the two years included in the study. 8,089 underwent CT scan first. 55% had IV only, 25% had IV and enteral contrast, and 12% had no contrast. The patients were evenly distributed across the groups. There did not appear to be a selection bias. This may have been a location-specific protocol.

The addition of enteral contrast added another hour to the patient’s emergency department stay.

What did they find? Concordance was 90% between the CT to the OR findings in the IV-only group. This was not changed with the addition of enteral contrast. Scans without contrast had 85.7% agreement. Scans with enteral contrast only also had a high agreement.

The authors found that the negative appendectomy rate was higher in the patients with enteral plus IV contrast than the group with IV contrast alone (3.5% versus 2.7%). They theorized that this was because one of the soft signs of appendicitis on CT scan is an appendix that doesn’t fill with enteral contrast, and there are other reasons the appendix may not fill with contrast.

Conclusion: There is no added value of enteral contrast even in a big wide vari- ety of cases, urban versus rural. There is no difference in diagnostic accuracy between IV and oral contrast versus IV contrast alone.