The functional pattern of the hypoplastic kidney.

Abstract

From a series of cases of unilateral small kidney those interpreted as renal hypoplasia and submitted to a split renal function study were selected for the present investigation. The results were compared with those obtained in a group of patients with unilateral renal artery stenosis as well as in cases of chronic pyelonephritis studied in the same fashion.In cases of hypoplasia the concentrating capacity of the smaller kidney sometimes approximated that of its fellow even when the difference in kidney size and filtration rate was very marked. On the whole, the concentrating capacity of both the smaller and larger kidney was better preserved in renal hypoplasia than in chronic pyelonephritis. The highest urinary osmolality and concentration index were observed in cases of renal artery stenosis and usually on the stenotic side.In the renal hypoplasia cases the efficiency of the smaller kidney in reabsorbing sodium under conditions of osmotic diuresis was nearly as good as that of the larger one—except in two cases. The two patients in whom a marked tendency to sodium loss was noted were the only normotensives in the hypoplasia group, in which hypertension was a predominant clinical feature.The side difference in filtration rate was considerably smaller in the renal artery stenosis and chronic pyelonephritis groups than in the hypoplasia cases, where the criteria for selection included a roentgenographic difference in kidney length of 2 cm or more.A split renal function study designed to give information on the filtration rate and the concentrating capacity as well as the excretion of ions under osmotic diuresis is of diagnostic aid when faced with the difficult problem of unilateral small kidney.