Epithelial abnormalities in the renal pelvis in experimental hydronephrosis and pyelonephritis

Unilateral hydronephrosis was induced by temporary ligature of the left ureter in 29 rabbits. In 21 animals so treated, chronic pyelonephritis was simultaneously induced by intravenous application of a suspension of E. coli. Histologic examination of renal pelvic epithelia in animals killed four weeks after the surgical intervention, revealed the following features: 1. Simple hyperplasia of urothelium in 12 cases, 2. atypical hyperplasia - (dysplasia) of urothelium in 10 cases, 3. v. Brunn's nests in 20 renal pelvises; 11 cases of cystic pyelitis, all combined with Brunn's nests, 4. metaplastic transformation of visceral mono- or bilayered epithelium into multi-layered urothelium-like structures in 19 renal pelvises. These changes are observed almost exclusively in the left renal pelvis of animals subjected to temporary ureteral ligature. Atypical urothelial hyperplasia is found only together with chronic pyelonephritis. Hyperplastic and dysplastic epithelial changes in the renal pelvis, the formation of Brunn's nests, and cystic pyelitis are interpreted as sequelae of postrenal obstruction or concomitant chronic inflammation.