Morphological and functional analyses of two infants with obstructive renal dysplasia.

Renal dysplasia associated with urinary tract obstruction comprises two distinct phenotypes, i.e., multicystic dysplastic kidney (MCDK) and obstructive renal dysplasia (ORD). MCDK is a common manifestation in infants with renal dysplasia, which is characterized by multiloculated thin-walled cysts with no functional parenchyma and an atretic ureter owing to pyelocalyceal occlusion early in fetal life. In contrast, ORD is an extremely rare condition which is caused by severe obstruction of the distal ureter or urethra. Here, we report two infants with ORD. Both patients manifested unilateral kidney enlargement with multiple cortical cysts, mild hydronephrosis, and marked dilatation of the ipsilateral ureter. Contralateral kidneys and urinary tracts revealed no apparent radiological abnormalities. Serial ultrasonographic studies of fetal and neonatal kidneys in both cases revealed that ureteral dilatation was evident at gestational week 16 and 27, respectively, and most of the cortical cysts disappeared within 1-3 months after birth. The functions of the affected kidneys were severely impaired but evident at the time of birth. These manifestations were consistent with a diagnosis of ORD, and were distinct from the features of MCDK. Our observation of fetal and infantile kidneys in these two cases provides us with a better understanding of the pathogenesis of ORD.