THE ASSESSMENT OF OBSTRUCTION IN THE NEWBORN WITH UNILATERAL HYDRONEPHROSIS BY MEASURING THE SIZE OF THE OPPOSITE KIDNEY

We measured the size of the normal kidney opposite a unilateral hydron ephrotic kidney in infants to determine if compensatory changes occurr ed and could be used as a diagnostic test for defining or excluding ob struction. Comparison of subgroups of neonates with unilateral hydrone phrosis or multicystic renal dysplasia to normal controls demonstrated that compensatory changes do occur in the normal kidney. Normal kidne ys opposite obstructed hydronephrotic kidneys requiring surgery became larger than normal for age. Normal kidneys opposite nonobstructed poo rly functioning hydronephrotic kidneys whose function rapidly improved were smaller than normal for age. These changes in renal growth by th e normal newborn kidney reflect renal counterbalance, which is exagger ated in this age group and which may be used to corroborate rapid chan ges in renal function caused by the presence or absence of obstruction . By plotting serial measurements of normal renal length on a renal gr owth chart, the diagnosis of obstruction in newborn hydronephrosis can be facilitated and the clinical management of the patient improved.