Renal Hypoplasia and Dysplasia in Infants with Posterior Urethral Valves

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Abstract
The morphology of 22 kidneys and the urinary tracts in 12 children who died of severe but incomplete urethral obstruction owing to posterior urethral valves showed many variations in structure. The dilatation of the calices and the thinness of the parenchyma may be explained on the basis of atrophy from back pressure of obstruction and reflux, but the etiology of variants, such as asymmetrical kidney morphologies, the occurrence of near normal renal parenchyma in some kidneys exhibiting all the ureteral and caliceal stigmas of severe obstruction and the high incidence of renal dysplasia, was not clear. The position of the ureteral orifices was known and available for this study, and the structure of the kidneys, using suitable methods of quantifying glomerular populations and dysplasia, was assessed for comparison and correlates. The renal morphology in these cases correlated with the position of the ureteral orifice, which in turn relates to the site of origin of the ureteral bud from the wolffian duct and the location of the corresponding segment of the nephrogenic cord induced by the bud. When this bud theory was invoked it was noted that those features of renal morphology that could not be readily explained by back pressure effects were accounted for more readily by the bud theory of renal development. A near normally placed orifice signified a near normal renal structure in the newborn, whereas lateral and diverticular orifices were associated with hypoplasia and hypodysplasia of the kidneys, respectively. It was concluded that incomplete urethral obstruction with or without reflux was not the primary cause of the structural anomalies of the kidneys; abnormal ureteral orifice positions denoted primary developmental malformations in the nephrogenic and stromagenic mesenchyme of the nephrogenic cord; and partial urethral obstruction together with reflux did not impair the subsequent nephron development in the fetus to any marked extent.