Normal renal ultrasound only rules out high grade vesicoureteral reflux in infants

1. Among infants in the first 2 months of life with febrile urinary tract infections (UTIs), the sensitivity and negative predictive value of renal ultrasound for diagnosing vesicoureteral reflux (VUR) increased as the graded severity of vesicoureteral reflux symptoms increased.

2. Patients without obstructive uropathies on voiding cystourethrogram (VCUG) all had normal findings on renal ultrasound. A normal renal ultrasound made the presence of grade IV-V VUR extremely unlikely but could not rule out grade I-III VUR.

Evidence Rating Level: 2 (Good)

Study Rundown: The most common manifestation of VUR in infants is a UTI, which may occasionally develop without noticeable symptoms. Systemic infection may occur when the direction of urine flow is reversed, causing reflux of urine from the bladder back into the ureters. This results in stagnant fluid accumulation in the ureters or renal collecting system creating an ideal environment for bacterial overgrowth. VUR is an anatomic abnormality most common in male infants secondary to posterior urethral valves but also may occur due to an abnormal angle of insertion of the ureter into the bladder. While there is little risk of long-term morbidity from isolated lower tract infections, cumulative injury from previously undiagnosed UTIs in the context of VUR in infancy may lead to renal scarring and long-term renal damage.  VUR is graded on a 5-point international grading system, from mild reflux (Grade I), when urine backs up just a short distance into the ureters, to severe reflux (Grade V), which can result in severe pyelonephritis and loss of renal function. Despite lack of consensus and robust evidence in this age group, diagnostic evaluation for VUR, obstructive uropathies, and urethral abnormalities following UTIs consists of ultrasound and the more invasive yet specific VCUG. The present study focused on the performance of ultrasound studies in infants less than 2 months old who presented with a first febrile UTI. The researchers reviewed medical records in which both VCUG and renal ultrasounds were performed. Abnormal findings on renal ultrasound were graded on the 5-point international VUR grading system and findings were cross-referenced to VCUG findings as the gold-standard. Their results indicate that the sensitivity and negative predictive value (NPV) of renal ultrasound in VUR detection increased proportionally to VUR severity on the 5-point scale. Thus, a negative renal ultrasound in an infant less than 2 months of age effectively rules out high grade VUR, but cannot preclude mild VUR. Study limitations included possible misdiagnoses secondary to the retrospective design, in addition to small sample size; further studies are needed to identify infant outcomes following febrile UTI and determine if renal ultrasound can prevent performance of unnecessary VCUGs.

Click here to read the study in the American Journal of Roentgenology

Relevant Reading: Relationships among vesicoureteric reflux, urinary tract infection and renal injury in children with non-neurogenic lower urinary tract dysfunction

In-Depth [retrospective cohort]: Medical records from 197 infants (67.5% male) aged less than 2 months with culture-confirmed, febrile UTIs were included in the study. Between July 2008 and December 2011, all subjects (age: 33 ± 15 days) received renal ultrasound and VCUG within 30 days of UTI diagnosis. Imaging findings were independently reviewed by two pediatric radiologists and selected for presence of dilation of the renal collecting system, renal size asymmetry, collecting system duplication, urothelial thickening, ureteral dilation, or bladder anomalies. In all, 25% (n = 49) had VUR grades I–V, with 16% (n = 31) having VUR grades III–V and 8% (n = 15) having VUR grades IV–V. Using VCUG as the reference standard, the sensitivity, specificity, PPV, and NPV of renal ultrasounds were calculated and it was determined that sensitivity and NPV of renal ultrasound in detection of VUR increased as VUR grade increased. Renal ultrasound had 32.7% sensitivity (CI₉₅: 20.0–47.5%) and 75.7% NPV (CI₉₅: 67.6–82.7%) for detecting low-grade VUR, 51.6% sensitivity (CI₉₅: 33.1–69.9%) and 89% NPV (CI₉₅: 82.5–93.7%) for detecting grades III–V VUR, and 86.7% sensitivity (CI₉₅: 59.5–98.3%) and 98.5% NPV (CI₉₅: 94.8–99.8%)for detecting grades IV–V VUR. Additionally, patients without obstructive uropathies on VCUG all had normal findings on renal ultrasound.

Image: PD

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