Can't See the Appendix on Ultrasound - Now What?

Written by Clay Smith

Spoon Feed
Don’t be falsely reassured if the appendix is not visualized on ultrasound in children - especially in boys, those with an elevated total WBC count, or elevated absolute neutrophil count.

Why does this matter?
A non-diagnostic appendix ultrasound is common, occurring in over half of pediatric studies. Prior studies suggested it was safe to send home kids with an incompletely visualized appendix if clinical exam was reassuring or the WBC count was low.

If the appendix ain’t appy, ain’t nobody appy.
This was a retrospective study of 3,245 children with abdominal pain and abdominal ultrasound to rule out appendicitis. In 54%, the appendix could not be visualized. Of these 1,764 children, they pulled out a random sample of 500 for chart review and found 11.9% were ultimately diagnosed with appendicitis. Of those who had additional imaging on the same visit, 21.2% were diagnosed with appendicitis. Of those who were discharged home, 1.5% had an ultimate diagnosis of appendicitis. Risk factors for having appendicitis after non-visualized appendix were, “male sex, leukocytosis, and an elevated absolute neutrophil count.” A major weakness of the study is that all patients were not reviewed. A random sample of 500 patients out of 1,764 means a margin of error of ~4%. Also, they were unable to contact 61% of discharged patients by phone. So, those discharged home who ultimately had appendicitis could be much higher than 1.5%. The real take home point is that if you can’t see the appendix on ultrasound and you clinically suspect appendicitis, you should either get additional imaging or consult surgery.

Another Spoonful
ALiEM has a really helpful post on combining pretest probability with ultrasound.

Source
Outcomes for Children With a Nonvisualized Appendix on Ultrasound. Pediatr Emerg Care. 2018 Nov 12. doi: 10.1097/PEC.0000000000001672. [Epub ahead of print]

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