US vs. CT – Combined Approach for Pediatric Appendicitis Diagnosis
April 2010
US vs. CT – Combined Approach for Pediatric Appendicitis Diagnosis
Search Strategy: .Searches performed via the TRIP database (http://www.tripdatabase.com) entering the terms “pediatric appendicitis imaging” yielded 12 hits via green color coding (“Highest yield evidence” i.e. Evidence Bases Synopsis, Systematic Reviews, Guidelines). You select the Doria article. The MEDLINE summary with 7 hits for Reviews and 57 hits for Diagnosis leads you to choose the Ramajaran article. Then you performed PUBMED search with “pediatric appendicitis imaging” that lead to 102 citations. This search yielded the Kaiser and Garcia articles.
You are working in the Pediatric Emergency Department and you have just seen a 9 year old boy with a 2 day history of periumbilical abdominal pain that has now ominously localized to the right lower quadrant. He has a fever of 101.5°F, nausea and vomiting. Based upon your physical examination you believe that this child has appendicitis. You order labs, urine, IV and call the radiologist to order an abdominal CT with contrast. However, your attending states that the ultrasound tech leaves in an hour. She emphatically declares “Let’s get the kid to ultrasound ASAP!”
You have not been in the pediatric ED in a long time and did not know that they were now pushing ultrasound. You question the best imaging modality for pediatric appendicitis.
PICO Question
Population: Pediatric patients with suspected appendicitis
Intervention: Abdominal ultrasound
Control: Abdominal computed tomography
Outcome: Sensitivity, specificity, likelihood ratio, reliability, availability, time-to-diagnosis, adverse effects of one diagnostic strategy over another
Years
Extra
As you review your articles, you find that you are concerned about the radiation exposure in children and would like to know more about the risk to discuss with families. You find two articles that help you answer the question of radiation exposure in pediatrics from computed tomography.
Articles
Article 1: Suspected Appendicitis in Children: US and CT—A Prospective Randomized Study, Radiology 2002; 233:633-638
ANSWER KEY
Article 2: An Interdisciplinary Initiative to Reduce Radiation Exposure: Evaluation of Appendicitis in a Pediatric Emergency Department with Clinical Assessment Supported by a Staged Ultrasound and Computed Tomography Pathway Acad Emerg Med 2009; 16:1258-1265
ANSWER KEY
Article 3: Selective Imaging Strategies for the Diagnosis of Appendicitis in Children, Pediatrics 2004; 13:24-28
ANSWER KEY
Article 4: US or CT for Diagnosis of Appendicitis in Children and Adults? A Meta-Analysis Radiology 2006; 241:83-94
ANSWER KEY
Bottom Line
| Sen (95% CI) | Spec (95% CI) | |
|---|---|---|
| Pediatric (US & CT) | ||
| US | 88 (86 – 90) | 94 (92 – 95) |
| CT | 94 (92 – 97) | 95 (94 – 97) |
| Adult (US & CT) | ||
| US | 83 (78 – 87) | 93 (92 – 96) |
| CT | 94 (92 – 95) | 94 (94 – 96) |
Several of these trials were hybrid diagnostic therapeutic-trial, but unfortunately they did not reference or follow the STARD or CONSORT guidelines. The biggest issue with these Pediatric-hospital based investigations is their limited external validity for EP’s who may lack a pediatric-surgeon or pediatric radiologist-sonographer 24/7.
In a pediatric hospital children evaluated by a Pediatric-Surgeon with suspected appendicitis can have the diagnosis confirmed with either Radiologist-performed compression sonography or intravenous contrast CT, but only CT can sufficiently rule out the diagnosis. One reasonable strategy in this setting would be US as first-line imaging study followed by CT if sonography negative but clinical impression remains high for appendicitis. To ensure external validity (i.e. reproducibility) this technology and diagnostic algorithm would need to be tested prospectively in pediatric and non-pediatric EDs staffed by EM physicians performing the initial evaluation and perhaps US testing.
A meta-analysis exploring the diagnostic accuracy of US or CT for appendicitis in children and adults yielded the following results:
Assuming an appendicitis prevalence of 15% than the number of cases of missed appendicitis by using US rather than CT would be 10 cases per 1000 children imaged and 18 cases per 1000 adult imaged. Conversely, if the prevalence of appendicitis is 75% than the number of cases of missed appendicitis by using US either than CT would be 48 per 1000 children imaged and 83 per 1000 adult imaged. Assuming a hypothetical sample prevalence of 0.31 for diagnosis of appendicitis in children, for every 10,000 children 11 years of age scanned with US rather than with CT, 280 would have a missed diagnosis of appendicitis and 13 could be prevented from developing cancer in the future. On the other hand, if we considered 10 000 adults 35 years of age scanned with US rather than with CT in a center with a sample prevalence of 0.40, the diagnosis of appendicitis would be missed in 480 patients, but only two patients could be prevented from developing cancer in the future. Therefore, two general considerations should be part of this conversation. First, CT should be increasingly preferred with higher appendicitis prevalence (i.e. in those with a higher pre-test probability). Second, future cancer risks are much smaller in adults so the CT-test threshold probably ought to be set lower than in children. But how much lower and where should that threshold be set?
A diagnostic RCT evaluated three strategies:
Strategy 1
Strategy 2
Strategy 3
* These investigators found the following characteristics in evaluating these strategies (Strategy #2 and #3 were hypothetical – not actually tested).
| Missed or Guideline | Delayed Dx (%) | Correct: Neg Appy (%) | Correct: Dx (%) | Imaging to avoid one missed/delayed Dx | Imaging to avoid one negative appy |
|---|---|---|---|---|---|
| 1 (CT + 43.5 US) | 6 | 5.9 | 94.0 | 19.2 CT + 27.4 US | 30.6 |
| 2 (CT + 31.9 US) | 6.1 | 6.2 | 93.8 | 17.7 CT + 20.4 US | 27.7 |
| 3 (CT + 16.4 US) | 6.3 | 9.7 | 92.4 | 11.1 CT + 15.9 US | 11.4 |
We conclude that selective imaging guidelines for pediatric patients with suspected appendicitis may reduce the number of radiographic studies performed, but prospective validation of both the risk stratification algorithm and the proposed imaging protocols at less specialized institutions are needed before these results can be confidently applied.