Functional characteristics of idiopathic hydronephrosis.

The functional characteristics of idiopathic hydronephrosis were studied in 171 patients. Conventional renography and measurement of the glomerular filtration rate were performed in all subjects, 137 (79%) of whom had normal parenchymal function despite severely reduced drainage function. Proximal tubular function, measured by determination of beta 2-microglobulin excretion was not reduced. Distal tubular function, evaluated as the maximum concentration ability, was not reduced in 35 of the 89 patients studied. During urography and diuresis renography were both useful tools for verifying the presence of obstruction in doubtful cases. Intrapelvic pressure was measured during constant perfusion at a rate of 7.5 ml/min and during furosemide-induced diuresis. The basal intrapelvic pressure varied from 6 to 10 cm H2O and was not increased in any kidney regardless of the degree of duration of obstruction. During perfusion, the pressure increased and varied from 28 to 52 cm H2O. During diuresis, an increase in pressure above 20 cm H2O was registered only in obstructed kidneys with a normal urinary concentrating ability. The pressure rise never exceeded 20 cm H2O during diuresis in obstructed kidneys with complications such as calculi of previous episodes of upper urinary tract infection. From these studies it is concluded that, besides cases with complications such as urinary tract infection and renal calculi, surgery should be offered to patients with idiopathic hydronephrosis with reduced urinary concentrating ability. In doubtful cases with wide pelves, renography and urography during increased diuresis can be used provided kidney function is not reduced. When kidney function is reduced, a pressure increase above 20 cm H2O during constant perfusion at a rate of 7.5 ml/min indicates obstruction.