Let’s move on to the next in the series of top ten articles presented at the 2014 AAP NCE in San Diego. Again, I’ll review the article and briefly and highlight how you can use the results in the ED.

By now, most of us have acknowledged that ultrasound is a fantastic imaging modality for the diagnosis of acute appendicitis. It is not, however the most sensitive and specific imaging test. That honor has gone to CT for many years running. MRI is here to challenge CT’s dynastic reign. MRI? But aren’t those expensive and impossible to get? A study published last April in PEDIATRICS would beg to differ.

Ultrasonography/MRI versus CT for diagnosing appendicitis

Aspelund G, Fingeret A, Gross E, Kessler D, Keung C, Thirumoorthi A, Oh PS, Behr G, Chen S, Lampl B, Middlesworth W, Kandel J, Ruzal-Shapiro C. PEDIATRICS, 2014
Links PubMed PEDIATRICS

The bottom line

In children with suspected acute appendicitis and an inconclusive ultrasound MRI is comparable to CT as follow up imaging

What they did

The authors retrospectively reviewed 662 patients that were evaluated for appy between 2008 and 2012. CT was used before 2010 (265 patients – 136 [51%] with positive appy), with ultrasound then MRI for confirmation thereafter (397 patients – 161 [41%] with positive appy). Data collected included time from triage to imaging and treatment and results of imaging and pathology. Ultimately they noted the following:

  • No difference in complicated appendicitis (perforation)by operative findings CT 32 (27.1%) vs US/MRI 33 (22.4%), p=0.4 or in pathology CT 17 (14.4%) vs US/MRI 18 (12.2%), p=0.7
  • No difference in negative appendectomy rate (on pathology) CT 3 (2.5%) vs US/MRI 2 (1.4%), p=0.7
  • Time to antibiotics did not differ CT 4.4 hours vs US/MRI 5.5 hours, p=0.07
  • Time to antibiotics did not differ CT 8.7 hours vs US/MRI 8.2 hours, p=0.14
  • Time to OR did not differ CT 13.2 hours vs US/MRI 13.9 hours, p=0.41
  • Hospital length of stay was similar between groups,  52.2 hours vs US/MRI 43.4 hours, p=0.18

In this study, the test characteristics of the imaging studies were as follows:

CT

  • Sensitivity 100% (95% CI, 97-100)
  • Specificity 98% (95% CI, 93-99)
  • PPV 98% (95% CI, 93-99)
  • NPV 100% (95% CI, 96-100)

Ultrasound/MRI

  • Sensitivity 100% (95% CI, 97-100)
  • Specificity 99% (95% CI, 97-100)
  • PPV 99% (95% CI, 95-100)
  • NPV 100% (95% CI, 98-100)

What you can do

  • You can consider ordering an MRI with contrast instead of a CT if you get an equivocal ultrasound for appendicitis as your diagnostic accuracy and time to important interventions may not differ
    • Obviously this is dependent on MRI availability, surgeon and radiologist availability and many more factors
  • Features considered diagnostic for ultrasound in appy include:
    • Noncompressible lumen
    • Diameter greater than 6-7 mm (98% sensitive)
    • Absence of gas in the lumen
    • Appendicolith
    • Thickened wall
    • Inflammatory changes surrounding the appendix may also be supportive
  • An equivocal ultrasound fails to show the appendix
  • Though not in the paper, know that MRI can actually be cheaper than CT
  • MRI also doesn’t expose patients to ionizing radiation