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 deve loping 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, reconstruc tions of dysplastic nephrons were done via serial section analysis. Early s tages of MCDK and ORD similarly revealed numerous cyst formations, predomin antly in the subcapsular nephrogenic zone. Occasionally, glomerular tuft re mnants with mature podocyte phenotypes were observed in cysts, suggesting t he acquisition of filtration. Three dimensionally, basic nephron structures were installed in the cystic nephrons, namely the macula densa with a prim ary loop structure. Cysts developed in the once-induced nephrons due to flu id retention in both MCDK and ORD. In utero urinary tract obstruction may c ause urine retention in functioning nephrons and lead to glomerular cysts i n the nephrogenic zone. These findings were common to MCDK and ORD, albeit at different sites of obstruction. Expansion of glomerular cysts with tubul ar dilatation (cysts) disturbs the subsequent nephrogenesis and may contrib ute to the misdevelopment of fetal kidneys.