Reduced kidney size in patients with simple renal cysts

Background. Renal cysts frequently occur in the absence of genetic diseases but their significance is unknown. Since multiple cysts develop in many patients with advanced renal disease, we tested the hypothesis that isolated cysts are associated with early nephron loss. Methods. All inpatient and outpatient sonograms performed by the Renal Division since 1995 were reviewed and, after exclusion of duplicate studies, patients with genetic cystic disorders, complex cysts, hydronephrosis, peripelvic cysts, end-stage renal disease and transplanted kidneys, 2526 were selected for this study, of which 385 had one or more cysts. Maximum renal length was used as an indication of size, and renal function was estimated by serum creatinine concentration. Results. Both right and left kidney length were significantly less in patients with cysts (P < 0.0001), independent of which kidney contained the cyst(s). Renal lengths were less in patients with multiple cysts as opposed to single cysts but not in patients with bilateral cysts as compared to unilateral cysts. Cysts were twice as frequent in solitary kidneys than in dual kidneys (P = 0.01). In outpatients matched for age and gender, those with cysts had a higher serum creatinine concentration but with borderline significance (P = 0.06). Multivariate analysis revealed that age, gender, and renal length were each independent variables and together accounted for one third of the incidence of cysts. Conclusion. Kidney size is reduced in patients with simple renal cysts noted on renal sonography, and cysts may be associated with reduced renal function. This suggests that isolated cysts are an indication of nephron loss in patients with renal abnormalities.