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MRI = CT for Appendicitis

September 24, 2018

Written by Clay Smith

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CT and MRI had similar diagnostic accuracy for acute appendicitis and may be used interchangeably.

Why does this matter?
CT is the gold standard test for acute appendicitis.  It has the disadvantage of ionizing radiation – not a trivial amount.  Would MRI be equally effective to diagnose appendicitis?

The magnet is an attractive option
This was a prospective study of 198 non-pregnant patients over age 12 who had CT ordered to rule out appendicitis.  All had both CT (with IV and PO contrast) and MRI (some with contrast, some without; with diffusion weighting) performed and read in random order by three radiologists who were blinded to final diagnosis or outcome.  The likelihood of appendicitis was rated from 1 to 5.  The gold standard for appendicitis was a composite of surgical, pathological, and clinical follow-up as determined by an expert panel.  Prevalence of appendicitis was 32.3%.  For a score of ≥3, the sensitivity of MRI was 96.9% vs 98.4% with CT; specificity for MRI was 81.3 vs 89.6% with CT.  When they used a rating cut point of ≥4, sensitivities were identical and specificities improved, and there was no statistical difference between CT and MRI.  Some patients had contrast for MRI and some did not. There was no difference in accuracy for non-contrast MRI, but the study wasn’t designed or powered for this outcome.  So, the two tests may be used interchangeably, but would this be feasible in practice? MRI takes much longer than CT to perform, which could increase length of ED stay.

Prospective Comparison of the Diagnostic Accuracy of MR Imaging versus CT for Acute Appendicitis.  Radiology. 2018 Aug;288(2):467-475. doi: 10.1148/radiol.2018171838. Epub 2018 Apr 24.
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Reviewed by Thomas Davis

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