Morphogenesis of nephropathy with partial ureteral obstruction and vesicoureteral reflux.

Hydronephrotic kidneys associated with partial ureteral obstruction and vesicoureteral reflux are similar and should exhibit similar morphology if the hydronephrosis was caused by abnormal urodynamic effects or back pressure. Kidneys with partial obstruction were compared quantitatively and statistically to kidneys with reflux to identify the macroscopic and microscopic structures that would indicate similar or dissimilar etiologies of the hydronephrosis. With partial ureteral obstruction the kidneys exhibited a generalized paucity of parenchyma, occurring in the cortex and medulla, and increasing with the degrees of hydronephrosis. Kidneys with reflux, and mild and similar grades of hydronephrosis compared to those of the obstructive forms were indistinguishable microscopically. Kidneys with reflux and more severe grades of hydronephrosis were different in that the cortex and medulla exhibited hypoplasia combined with dysplasia and, although the cortex was approximately equal in thickness, the glomerular counts were smaller. These features in kidneys with reflux were proportional to the degree of lateral ectopia of the corresponding ureteral orifice. Obstructive atrophy of renal parenchyma explains the morphology of the obstructive hydronephrosis, whereas the hypoplasia and dysplasia corresponding with orifice position in the kidneys with reflux are explained more readily by the bud theory, in which the ureteral bud, metanephric mesenchyme and induction capabilities of each are all at fault. In the absence of infection the kidneys may undergo progressive atrophy with partial obstruction of the ureter, whereas the kidneys with reflux exhibit performed grades of hydronephropathy, which are determined embryologically.