Renal parenchymal fibrosis and atrophy are not correlated with upper tract dilatation: long-term study of partial unilateral ureteral obstruction in neonatal mice.

Purpose: The mechanism underlying the evolution of congenital obstructive hydronephrosis is still unclear. In a previous study, we have shown that it is possible to create renal lesions in newborn mice specific to partial ureteral obstruction. We aimed to study the long-term results of such partial obstruction.

Methods: Mice were operated on the third day of life. We created 2 groups: partial unilateral obstruction and control. We studied antero-posterior pelvis diameter, kidney length and volume on magnetic resonance imaging at day 10 and 3 months. We assessed ureteric patency by injecting Patent Blue dye. Kidney weight and fibrosis were histologically assessed. Fibrosis was assessed using Sirius Red staining and morphometry.

Results: Imaging showed parenchymal atrophy in the partially obstructed kidney and compensatory hypertrophy of the contralateral kidney. Pelvis dilatation was detected at day 10 but remained stable without significant increase at 3 months. The patency test confirmed the absence of total obstruction in the long term. There was no correlation between the degree of dilatation and parenchymal atrophy or the contralateral hypertrophy. Pathological studies at 3 months revealed fibrosis in the parenchyma without significant correlation with pelvis dilatation.

Conclusions: Long-term results confirmed that partial ureteral obstruction in newborn mice produces fibrotic lesions of the renal parenchyma, which are not correlated with dilatation of the upper tract. These results could contribute to the clinical management of obstructive uropathy in children, emphasizing that follow up with simple evaluation of upper tract dilatation is insufficient to predict renal deterioration.