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Renal ultrasound to evaluate for blunt renal trauma in children: a retrospective comparison to gold standard diagnostic test study
Angelena Edwards, M.D., Matthew Hammer, M.D., Maddy Artunduaga, M.D., Craig Peters, M.D., Micah Jacobs, M.D., Bruce Schlomer, M.D..
UT Southwestern, Dallas, TX, USA.

Title
Renal ultrasound to evaluate for blunt renal trauma in children: a retrospective comparison to gold standard diagnostic test study
Introduction
The standard imaging modality for hemodynamically stable blunt abdominal trauma patients is a contrast enhanced CT scan, which is reflected in the current AUA urotrauma guideline. This comes, however, at the price of increased radiation exposure and the potential sequalae of IV contrast administration in the pediatric patient. When the majority of pediatric hospitals have ultrasound readily available, the use of initial CT imaging for these patients can be seen as being in direct opposition of the ALARA principle. We hypothesized that ultrasound imaging would be able to identify clinically significant injuries when compared to CT scan in the setting of pediatric blunt abdominal trauma.
Methods
All children < 18 years of age who were evaluated for blunt abdominal trauma were identified. A clinically significant renal injury was defined as an AAST grade three or above or an injury that prompted a procedure. Significant hematuria was defined as episode of gross hematuria or >50 RBC/HPF. Those patients who had a CT and ultrasound imaging of the kidneys within three weeks of injury were included. Clinical information was obtained from the medical record including degree of hematuria and clinical outcomes. The ultrasound images were reviewed by four reviewers (two pediatric urologists, two pediatric radiologists) who were blinded to CT results and all clinical information other than the patient's history of blunt abdominal trauma. The ability of ultrasound with and without the combination of significant hematuria to diagnose and rule out renal injury was evaluated by sensitivity and negative predictive value (NPV).
Results
There were 76 patients identified, 24 of which had a renal injury diagnosed by CT scan. There were five grade I-II injuries, ten grade III, eight grade IV and one grade V. The sensitivity of the four blinded reviewers for ultrasound alone to detect the 19 children with grade III-V injuries ranged from 79-100% with NPV between 93-100%. When combined with significant hematuria, all reviewers identified the 19 patients with grade III-IV injuries with a NPV of 100%. Of note, all patients with grade III-V injury of the kidney had significant hematuria. Of the grade I-II renal injuries, all four reviewers identified 1/5 by ultrasound alone and 2/5 by ultrasound combined with significant hematuria.
Conclusions
When compared to a CT scan as gold standard, blinded review of kidney ultrasound images had a sensitivity of 79-100% to detect grade III-V injuries and NPV of 93-100%. An episode of gross hematuria or > 50 RBC/HPF had sensitivity and NPV of 100% for grade III-V injuries. Therefore, ultrasound did not identify any additional patients with a grade III-V injury. CT scans to rule out renal injury can potentially
be avoided in children with blunt abdominal trauma who do not have significant hematuria, especially if kidneys are normal on ultrasound.


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