Hydronephrosis with diffuse or segmental cortical thinning: Impact on renal function

Purpose: Management of hydronephrosis has changed considerably with the routine use of prenatal ultrasonography. Increased dependence is now placed on nuclear renographic differential renal function, and many urologists consider surgical intervention for ureteropelvic junction obstruction with significant decrease in renal function (less than 40%). Correlation between differential renal function and the degree of dilatation diagnosed by ultrasound has not been reported. In addition, no difference between hydronephrosis associated with either diffuse or segmental cortical thinning has been made, as both are classified as grade IV according to the Society of Fetal Urology classification. Based on clinical observation we hypothesized that hydronephrotic grade TV kidneys with diffuse parenchymal thinning are associated with worse renal function and are distinct from those with segmental cortical thinning. Materials and Methods: We performed a retrospective study of patients who underwent pyeloplasty between January 1996 and December 1998. Hydronephrosis was graded according to Society for Fetal Urology classification and all diuretic renograms were performed in a standardized fashion. Grade TV kidneys were divided into IVA (segmental cortical thinning) and IVB (diffuse cortical thinning). Statistical correlation of grade and differential renal function was performed using a chi-square test. Results: Images were available for review in 77 patients. Average patient age at intervention was 20.4 months and 7.6 years of the prenatally and postnatally detected hydronephrosis groups, respectively. Of the 77 cases 25 had grade IVA and 18 had grade IVB hydronephrosis. Of the grade IVB hydronephrosis cases 66% had less than 40% differential renal function compared to 24% in group IVA (p <0.05). Conclusions: Patients with grade IVB hydronephrosis secondary to ureteropelvic junction obstruction have a higher risk of significant decrease in renal function. Group IVA has significantly better function than group IVB and characteristics similar to grade III hydronephrosis cases. Grade IVB hydronephrosis should monitorized closely as earlier intervention may be warranted to avoid progressive deterioration of renal function.