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BACKGROUND:Vesicoureteral reflux (VUR) is a common pediatric urological condition that is diagnosed with invasive voiding cystourethrogram (VCUG). Renal and bladder ultrasonography (RBUS) has low specificity for VUR and renal scarring. We propose that RBUS derived renal parenchymal area (RPA) may be a quantitative parameter with which to evaluate VUR risk in children with UTIs as well as risk of renal scarring in children with VUR.
METHODS:With IRB approval, we retrospectively identified children less than 18 years who had a VCUG from 2000-2009 for evaluation of UTI and also had RBUS within 6 weeks of the VCUG. Children with prior diagnosis of VUR and systemic disease were excluded. RPA for left and right kidneys were obtained from supine ultrasonic images using NIG Scion imaging software. RPA for left, right and sum kidneys were analyzed by patient age and VUR status. RPAs from the initial ultrasound after UTI diagnosis were plotted against age adjusted RPA normal curves that were separately determined. Children who had at least three RBUS during follow up had RPAs plotted longitudinally to determine renal RPA variation over time. The RBUS results reported by pediatric radiologists were also evaluated.
RESULTS: A total of 5380 VCUGs were performed during the time period, of which 1273 VCUGs met inclusion criteria. Of these, 603 VCUGs (47%) were performed after first UTI. Of children undergoing VCUG for one or more UTIs, 455 (35.7%) had VUR. Of children undergoing VCUG after the first UTI, 189 (31.3%) had VUR. 245 (53.8%) of children with one or more UTIs had a VUR grade three or greater. Children without VUR fell along the normal distribution of the RPA growth curve. Children with bilateral grade four and greater VUR were had significantly different RPA from children with no VUR (p= 0.02). RBUS report identified 11% of VUR grade three and above whereas RPA falling one and two standard deviations below the normal predicted 15.4% and 38.5% of VUR grade three and above, respectively. When followed for an average of 43 months, children with bilateral high grade VUR (Gr 3-4 and above) did not show significant “catch up” in the RPA and two out of seven (28%) had a decline in RPA over time.
CONCLUSIONS:RPA is more likely to be abnormal in patients with high grade VUR compared to those without VUR. RPAs that fall one to two standard deviations below the normal curve can identify high grade VUR, and based on the number of standard deviations below the normal curve may be more sensitive than an ultrasonic report of “small or scarred” kidney. RPA may be useful for risk stratifying children who will benefit from VCUG following UTI as well as those children who should be followed for possible renal damage.