Congenitally small kidneys with reflux as a common cause of nephropathy in boys.

Congenital maldevelopment is sometimes found in small kidneys with ureteral reflux. However, the incidence of congenitally small kidneys and the frequency of its association with ureteral reflux remains unknown. Ultrasound scanning, performed in 4,000 apparently healthy neonates or young infants (males 2,129, females 1,871), detected 51 children suspected of having small kidneys. A careful ultrasound re-examination performed one month later in 45 of the 51 children confirmed small kidneys in eight children, one bilateral and seven unilateral. Dimercaptosuccinate (DMSA) renoscintigraphy revealed small kidneys with generally diminished uptake in six infants and no uptake unilaterally in the other two infants. One of the 12 children, who had normal findings on the initial scanning and subsequently developed urinary infection, was later diagnosed having unilateral small kidney with generally reduced DMSA uptake. All seven infants having small kidneys with reduced tracer uptake were male (incidence, 1:300 boys). All eight small kidneys in the seven boys and four of the six contralateral non-small kidneys were associated with ureteral reflux, while neither of the two infants with a non-functioning kidney had ureteral reflux. Serial ultrasounds documented the poor growth of all small kidneys. Thus, congenitally small kidneys with generally diminished DMSA uptake were highly associated with ureteral reflux and especially observed in boys.