Low-dose computerized tomography does not compromise clinical outcomes in pediatric nephrolithiasis
Julie W. Cheng, MD, MAE1, Dima Raskolnikov, MD2, Nicolas Fernandez, MD, PhD1, Jonathan D. Harper, MD2, Grace S. Phillips, MD1, Paul A. Merguerian, MD, MS1.
1Seattle Children's Hospital, Seattle, WA, USA, 2University of Washington, Seattle, WA, USA.
BACKGROUND: Medical imaging and surgical treatment for pediatric nephrolithiasis can expose patients to ionizing radiation. Although ultrasound is recommended as an initial imaging modality to screen for nephrolithiasis, there are instances in which computed tomography (CT) imaging may be necessary if ultrasound is equivocal. The efficacy of low-dose CT imaging has been demonstrated in adults, but reports are limited in pediatric patients. The purpose of this study was to evaluate radiation exposure and clinical outcomes related to the implementation of a low-dose CT protocol for pediatric patients with suspected nephrolithiasis.
METHODS: This study was approved by our institutional review board. A low-dose CT protocol was implemented October 2019 and applied if ultrasound was non-diagnostic for nephrolithiasis. Patients <21 years that presented to the emergency department (ED) and underwent CT for suspected nephrolithiasis from October 2017 through September 2021 were included. Patients were divided into two groups. The pre-protocol group included patients that underwent imaging in the 2 years prior to protocol implementation. The post-protocol group included patients that underwent imaging in the 2 years following protocol implementation. Retrospective chart review was completed for demographic information, clinical presentation, imaging characteristics, and clinical outcomes. Primary outcomes included radiation exposure measured by effective dose and dose-length product (DLP). Secondary outcomes included missed stone diagnosis, hospital admission, return to the ED, and stone management.
RESULTS: 54 patients underwent CT imaging for nephrolithiasis in the ED with 15 (27.8%) patients in the pre-protocol group and 39 (72.2%) patients in the post-protocol group. Patient demographics and clinical presentation did not differ between the two groups. 28 (51.9%) patients had stones identified on CT imaging. Median effective dose (Figure 1) was significantly lower in the post-protocol group with 2.27 mSv compared to 4.68 mSv in the pre-protocol group (p=0.024). DLP was also significantly lower in the post-protocol group (p=0.025). This difference remained significant after adjusting for weight (p=0.002) and anterior-posterior diameter (p=0.005). There were no statistically significant differences between the two groups with regard to nephrolithiasis (p=0.437) or hydronephrosis (p=0.224) on CT imaging. Amongst patients that underwent imaging after CT, no undiagnosed stones were detected on repeat imaging in either group. Clinical outcomes did not differ between the two groups with regard to hospital admission (p=0.671), length of stay (p=0.421), return ED visits (p=0.331), or stone management (p=0.144). There were 21 patients with stones that underwent trial of passage and 7 that underwent semi-urgent decompression with stent placement followed by subsequent ureteroscopy.
CONCLUSIONS: Low-dose CT KUB protocols can effectively reduce radiation exposure for pediatric patients that require cross-sectional imaging to evaluate renal colic without affecting clinical outcomes. If an initial ultrasound is limited in evaluating pediatric nephrolithiasis, low-dose CT should be the standard of care in place of conventional CT. 
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