IMAGING

Imaging in pediatric urinary tract infection: a 9-year local experience
Luk WH, Woo YH, Au-Yeung AW, Chan JC
Department of Diagnostic Radiology and Organ Imaging, United Christian Hospital, Kowloon, Hong Kong
AJR Am J Roentgenol. 2009; 192: 1253-60

• Objective: Urinary tract infection (UTI) is a common disease entity in children, and a number of imaging options are offered for these patients. The purpose of our study was to retrospectively describe the (99m)Tc-labeled dimer captosuccinic acid (DMSA) renal scintigraphy, ultrasound, and micturating cystourethrography (MCU) findings over a 9-year period.
• Materials and Methods: All children younger than 10 years old who presented to a local hospital in Hong Kong between July 1, 1997, and June 30, 2006, with culture-confirmed UTI and who subsequently underwent DMSA scintigraphy, ultrasound, and MCU were identified. For the purpose of this study, patients with underlying major congenital urinary tract abnormalities were excluded. DMSA scintigraphy was regarded as the gold standard for the diagnosis of renal scarring. DMSA scintigraphy, ultrasound, and MCU findings and clinical outcomes were reviewed and analyzed.
• Results: A total of 583 children were included in the study. Of these, 432 children (74.1%) had normal findings on ultrasound and on MCU. Only 13 children (3%) of this group had renal scarring as shown on DMSA scintigraphy. The overall negative predictive value (NPV) for excluding renal scarring of combined ultrasound and MCU reached 97%. The NPV was 97.7% in the subgroup of patients 0 to 2 years old.
• Conclusion: For children younger than 2 years with UTI in the absence of underlying major congenital urinary tract abnormalities, we recommend that DMSA scintigraphy may be withheld if findings on both ultrasound and MCU examinations are normal.

• Editorial Comment
  The authors performed a retrospective study in order to evaluate the potential role of combined ultrasound (US) and MCU as first-line imaging tests in predicting renal scarring using DMSA scintigraphy as the gold standard. In their cohort, almost 600 children were included. The performances of US alone, MCU alone, and the techniques combined were systematically evaluated and compared with the performance of DMSA scintigraphy. If US alone was performed, the probability of missing renal scarring was as high as 7.2% compared to 3.1 % with MCU alone. If MCU and US were considered together, the probability of missing renal scarring could be further reduced to 3.0%. A normal US and normal MCU therefore would safely exclude renal scarring in most cases with a false-negative risk of 2.3% in children younger than 2 years. The authors concluded that DMSA scintigraphy may be withheld in children younger than 2 years in the absence of major congenital urinary tract abnormalities. For children with either positive US or positive MCU findings, further evaluation with DMSA scintigraphy should be performed to determine whether scarring is present.
  In this study, DMSA scintigraphy was generally performed a minimum of 3 months after the onset of UTI. As we know there is on going debate in order to establish the most adequate timing to perform DMSA scintigraphy since pyelonephritis and renal scarring looks similar on DMSA scans (1). In other words, it is difficult to determine at what time point a scintigraphic defect should be considered permanent scarring rather than potentially recovering pyelonephritis. Up to now there is no consensus regarding the length of time after the initial episode of UTI that this follow-up DMSA scanning for scarring should be performed. In the literature, this length of time varies from 3 months to 12 months. As we can see, we are still distant from following accurate strict guidelines in imaging protocol in these children.

Reference
1. Lim R: Vesicoureteral reflux and urinary tract infection: evolving practices and current controversies in pediatric imaging. AJR Am J Roentgenol. 2009; 192: 1197-208.

Dr. Adilson Prando
Chief, Department of Radiology and
Diagnostic Imaging, Vera Cruz Hospital
Campinas, São Paulo, Brazil
E-mail: adilson.prando@gmail.com