Renal histology in ureteropelvic junction obstruction:: Are histological changes a consequence of hyperfiltration?

Purpose: There are few reports of pathological kidney findings in ureteropelvic junction obstruction in pediatric patients. The role of hyperfiltration in the genesis and progression of these changes has been a matter of debate. We determine whether segmental sclerosis is evidence of hyperfiltration and renal damage in children who underwent surgery for ureteropelvic junction obstruction. Materials and Methods: We retrospectively analyzed the clinical records of 38 children with a mean age of 4.4 years with ureteropelvic junction obstruction. Histological changes in biopsies (39 renal units) and nephrectomy specimens (2 renal units) were compared with clinical history, imaging studies and urinary protein excretion. Results: Renal histology was essentially normal in 75% of the biopsies. Focal dilatation of Bowman's space and occasionally of the collecting tubules was noted in a third of this group. Abnormal changes consistent with renal damage were present in 25% of the biopsies, including variable degrees of interstitial chronic inflammation, eosinophilic acellular material within Bowman's space and focal concentric glomerulosclerosis. Severe changes, chronic interstitial fibrosis and inflammation, and diffuse glomerulosclerosis were only found in nephrectomy specimens, while eosinophilic acellular material and glomerulosclerosis were observed in 7 biopsies; In all of these renal units there was evidence of hyperfiltration with bilateral or unilateral ureteropelvic junction obstruction with a contralateral multicystic dysplastic kidney. Urinary protein excretion in 19 patients was increased in obstructed compared with normal contralateral kidneys (p <0.05). Conclusions: Hyperfiltration should be considered a mechanism involved in the progression of histological changes in kidneys with ureteropelvic junction obstruction. We suggest that early surgical correction be considered in obstructed kidneys at risk for hyperfiltration.