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Renal maldevelopment: a pediatric renal biopsy study.

We reviewed 18 pediatric open renal biopsies performed because of renal insufficiency in patients with renal or renal and lower urinary tract (LUT) anomalies. Nine patients had LUT anomalies, 6 had small kidneys, and 3 had normal-sized, enlarged polycystic, and ectopic kidneys, respectively. Patients with LUT anomalies underwent biopsy at an earlier age and had a higher incidence of extrarenal anomalies. Seventeen biopsy specimens were abnormal: 15 showed focal forms of renal dysplasia, and 1 biopsy each showed glomerulocystic kidney disease and dominant polycystic kidney disease. The specimens with dysplasia also contained normal-looking nephrons, whose numbers were particularly striking in patients with a normal LUT. The biopsy specimen from the ectopic kidney was normal. Progressive renal disease developed in 12 of 17 patients with follow-up. All of them had either bilateral uncorrectable LUT abnormalities or bilateral small kidneys. This study demonstrates that renal biopsies in patients with renal insufficiency and gross abnormalities in kidneys or the LUT will often show evidence of parenchymal maldevelopment, principally focal forms of renal dysplasia Although normal nephrons are also present, and might even predominate, progressive disease should be anticipated in the presence of bilateral involvement because of the underlying developmental abnormality coupled with complications related to LUT disease and deficiency in renal mass.