Initial pathological events in renal dysplasia with urinary tract obstruction in utero.

Multicystic dysplastic kidneys (MCDK) and obstructive renal dysplasia (ORD) are two different phenotypes of dysplasia commonly associated with urinary tract obstruction. However, the mechanisms whereby obstruction in the developing kidney leads to each dysplasia are unknown. In the present study, 16 fetal MCDKs and 3 fetal ORDs (18-35 weeks of gestation) were analyzed with light microscopy, point-counting morphometry, immunohistochemistry with a podocyte marker, and scanning electron microscopy. Additionally, reconstructions of dysplastic nephrons were done via serial section analysis. Early stages of MCDK and ORD similarly revealed numerous cyst formations, predominantly in the subcapsular nephrogenic zone. Occasionally, glomerular tuft remnants with mature podocyte phenotypes were observed in cysts, suggesting the acquisition of filtration. Three dimensionally, basic nephron structures were installed in the cystic nephrons, namely the macula densa with a primary loop structure. Cysts developed in the once-induced nephrons due to fluid retention in both MCDK and ORD. In utero urinary tract obstruction may cause urine retention in functioning nephrons and lead to glomerular cysts in the nephrogenic zone. These findings were common to MCDK and ORD, albeit at different sites of obstruction. Expansion of glomerular cysts with tubular dilatation (cysts) disturbs the subsequent nephrogenesis and may contribute to the misdevelopment of fetal kidneys.