Renal Dysplasia with Hydronephrosis and Congenital Ureteral Stricture in Two Holstein-Friesian Calves.

We investigated the pathological characteristics of renal dysplasia with hydronephrosis and congenital ureteral stricture in two calves. Macroscopically, the affected kidneys were enlarged and the renal calyces were dilated and associated with ureteral strictures. Histopathologically, multifocal regions of mesenchyme were observed in the renal medulla. This mesenchyme was weakly eosinophilic with haematoxylin and eosin, blue with Alcian blue and pale blue with Masson's trichrome, and was immunopositive for vimentin and smooth muscle actin, consistent with persistent mesenchyme. There was asynchronous differentiation of the renal cortex characterized by immature glomeruli, immature tubules and arteriolar proliferation. Similar persistent mesenchyme was observed in the ureteral walls with ureteral stricture, and the ureteral musculature or smooth muscle bundles had a disorganized arrangement. Congenital ureteral stricture appeared to have caused ureteral obstruction and hydronephrosis. The lesions may represent a new phenotype of renal dysplasia with concomitant congenital ureteral stricture in Holstein-Friesian calves.