Renal biopsy in congenital ureteropelvic junction obstruction: evidence for parenchymal maldevelopment.

The renal histologic changes associated with congenital ureteropelvic junction obstruction (UPJO) and the relationship to clinical imaging have not been well studied. In order to better understand the histologic alterations of congenital UPJO and their relationship with clinical imaging and outcomes, we examined renal biopsies from 61 patients undergoing pyeloplasty for congenital UPJO. Glomeruli were analyzed for various injury patterns and the tubulointerstitium was examined for tubular atrophy/simplification and fibrosis. Two methods were used to evaluate tubular mass: glomerular density and morphometric measurement of tubular size and density. Control specimens were obtained from age-matched autopsy specimens without renal pathology. Glomerular changes were identified in 73% of all biopsies and were present in a range from 1.7 to 91% of glomeruli in each patient. Overt tubulointerstitial changes were present in 26% of all biopsies. Fibrosis was noted to occur with tubulointerstitial changes in a significantly greater fraction of children over the age of 1 year (P=0.026). Increased glomerular density was associated with severe hydronephrosis (P<0.02). Normal glomerular density was inversely correlated with age (P<0.001), but this relationship was more variable in UPJO (P<0.01). Among patients with intact differential function preoperatively (>45%), postoperative functional decline was predicted only by increased glomerular density. 20 biopsies without overt tubulointerstitial changes were analyzed morphometrically and showed a significant reduction in proximal tubular (PT) size, but unchanged density. Distal tubular (DT) size was unchanged in UPJO, but density was increased. The PT/DT ratio was therefore markedly decreased in UPJO (P<0.0001). Both PT and DT sizes were significantly larger in children with a diuretic renogram washout time less than 20 min than those with greater than 20 min, a common threshold for functionally significant obstruction (P<0.05). Capsular thickness was significantly increased in UPJO. In all, 36% of biopsies had a thickness >0.5 mm and this was associated with greater degrees of tubulointerstitial changes and glomerular alterations. Congenital UPJO produces a variety of renal parenchymal changes, which may in part reflect abnormal development. Some of these alternations are seen in clinical imaging and may help predict outcomes, but there is significant discordance between conventional imaging and histological findings.