Since the introduction of prenatal and postnatal examination of the kidneys there háve been increasing numbers of children with the diagnosis of renal pelvic dilatation. There is still no simple test, which would differentiate non-obstruction hydronephrosis, where a conservative proceduře is possible, from obstruction, which requires a surgical solution. The dynamic scintigraphy of the kidneys is ušed for the demonstration of obstruction. A decrease of relative function of the affected kidney below 40% is considered to pro ve the obstruction as well as an obstruction shape of nephrographic curve. The aim of this work was to compare histological findings in children operated on hydronephrosis with preoperation examinations. Fifty children, who háve been operated on hydronephrosis at the Urological Clinic of Faculty Hospital in Olomouc in the years 2000 - 2003, entered the study. Children with associated anomalies (vesicoureteral reflux, megaurether) were excluded. A wedge-shaped biopsy of the kidney was performed during the operation and the sampled obtained was examined by histology. The findings were categorised into four histological groups according to Zhang. A normál histological finding was found in four out of 50 surgically treated children, mild histological findings were in 15 of them, medium severe changes were in 24 subjects and severe morphological findings were in seven patients. In the 24 patients with medium severe changes, only five subjects suffered from decreased relative function of the kidney. The examination in the other subjects revealed function within physiological values. The obstruction type of the curve was in about the samé frequency in children with mild histological changes and in those with severe defect. A repeated ultrasonography proved to be a relatively sensitive examination as well as progressed reduction of parenchyma. Conclusion: A relative decrease of kidney function during scintigraphic examination occurs almost exclusively in patients with a severe defect of the kidney. This kind of examination does not reveal patients, whose relative function is still normál, but a histologically demonstrable irreversible defect of kidney parenchyma is already present.

        Key words: hydronephrosis, dynamic scintigraphy, tubulointerstitial fibrosis, glomerulosclerosis