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Ultrasound Imaging for Appendicitis

Ilene Claudius, MD and Ann Dietrich, MD
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Ilene discusses the use of ultrasound in children with abdominal pain.

Pearls:

  • In appendicitis, ultrasound should not be seen as a test with a dichotomist result.  That is, it is either “positive or negative”.  It should be used in conjunction with the clinical exam and/or laboratory studies.

  • In patients with symptoms < 48 hours, ultrasound findings may not reveal appendicitis and inflammatory markers may not have had time to rise.

  • Ultrasound should be used to confirm but not definitively exclude appendicitis.  The sensitivity of ultrasound is between 78 and 99%.  

 

  • According to the 2010 ACEP guidelines, ultrasound (US) should be used as the initial imaging in children with suspected appendicitis. It should be noted that some children, in some centers, have no imaging before being taken to the operating room for suspected appendicitis.  This is usually in situations in which clinical characteristics and laboratory findings are significant.  

  • When do you not use ultrasound?  US  is not indicated in patients who are being taken to the OR emergently. Ultrasound is less accurate in patients with a BMI > 85th percentile, patients with “tip appendicitis” (ie inflammatory changes in the distal appendix), retrocecal appendicitis, those patients who have a shorter duration of symptoms (< 48 hours) and/or a < 50% pretest probability. US is also not good for determining perforation.

  • When is secondary imaging recommended? To answer this question, it is important to remember that what is defined as a positive, negative and/or equivocal US is not well defined in the literature. Generally, however, an accepted definition is that a positive US for an appendicitis is a tubular, non-compressible structure > 6 mm in diameter.  In a patient with these findings and a clinical exam consistent with appendicitis, no further imaging is indicated. One uses the US and pretest probability to decide on further imaging.

    • For example, if the US shows an appendicolith, hyperechoic para-appendiceal fat, loss of the echogenic submucosal layer, increased blood flow and/or appendiceal fluid collection, these are equivocal findings and the next step depends on your pre-test probability.  If your clinical exam suggests appendicitis and the US is equivocal, than further imaging would be indicated. If you are unsure of your clinical exam, watchful waiting may be appropriate with a 12 hour follow up.  Observation may occur at home or in the urgent care setting. Repeat US at that time might be indicated

      • Asking the patient to return in a couple of days is not appropriate.

Schuh S et al.  Properties of serial ultrasound clinical diagnostic pathway in suspected appendicitis and related computed tomography use.  Acad Emerg Med. 2015. Apr;22(4):406-14.  PMID: 25808065

  • If the appendix is not visualized, there is still a 6-12% chance of appendicitis.  

  • MRI sensitivity for appendicitis is 97%.  Some centers have MRI protocols which include an 8 minute focal MRI of the right lower quadrant.  If MRI is not available and/or feasible, second line imaging should be a CT with IV contrast.  CT has a great specificity early on in the course of appendicitis.    

Ramarajan, N. Clinical correlation needed: what do emergency physicians do after an equivocal ultrasound for pediatric acute appendicitis? J Clin Ultrasound. 2014. Sept;42(7):385-94. PMID: 24700515

  • How do you use labs and determine your pretest probability? A WBC > 10, is 83% sensitive and a CRP > 10 is 60-70% sensitive.  Remember CRP starts to rise at 8 hours and doesn’t peak until 24-48 hours of symptoms.  Neutrophils > 75% have between a 66 and 87% sensitivity. All of these should be used as data points in conjunction with your clinical exam and imaging findings. Labs can be helpful if there are many other diagnosis on your differential; specifically constipation, in which you would not expect elevated inflammatory markers.  

  • What about imaging in younger children? Not much literature exists on this topic. One study, referenced below, suggests that when children under 5 are taken to the OR based on US findings, there is a paradoxically higher negative appendectomy rate. The little literature that exists, suggests that US should be interpreted cautiously in children under 5, especially in children under 3.

    • This is concerning because the rupture rate in younger children is higher than in older children.  

Bachur, RG et al.  Diagnostic imaging and negative appendectomy rates in children: effects of age and gender. Pediatrics. 2012. May;129(5):877-84. PMID: 22508920

As always, it is important to maintain a broad differential in a child with abdominal pain. In males, even infants, testicular torsion should be considered and in girls, ovarian torsion must be considered.  

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