The antegrade nephrostogram is an important tool in the evaluation of the upper urinary tract. However, the information currently provided by a nephrostogram is largely limited to anatomical details. To establish a meaningful pressure-flow parameter that may be incorporated into a routine nephrostogram, we evaluated the ureteral opening pressure (defined as the pressure at which contrast material is first seen beyond the suspected site of obstruction) and correlated these findings with the results of pressure-flow studies performed with an external infusion and/or furosemide induced diuresis.Materials and Methods
A total of 52 renal units were studied under a prospective pressure-flow study protocol. All patients had grade 3 or 4 hydronephrosis (Society of Fetal Urology classification) and patient age range was 0.2 to 12 years (median 1.1). The suspected sites of obstruction were the ureteropelvic and ureterovesical junctions in 42 and 10 renal units, respectively. With the patient under general anesthesia 22 gauge percutaneous nephrostomy needles were inserted. Pressure-flow studies with an external infusion and/or furosemide induced diuresis were then performed. As the renal pelvic pressure progressively increased during the course of the pressure-flow studies, the renal pelvic pressure at which contrast material was first seen to appear distal to the suspected site of obstruction was recorded as the ureteral opening pressure. Ureteral opening pressures were compared to the results of the pressure-flow studies.Results
With a positive test defined as renal pelvic pressure greater than 14 cm. water, positive ureteral opening pressures were associated with positive pressure-flow study results in 100% of the cases, regardless of which form of pressure-flow study was used or where the suspected site of obstruction was located. In contrast, negative ureteral opening pressures had specificities and negative predictive values of only 19 to 57%, depending on the form of the pressure-flow study and the suspected site of obstruction.Conclusions
An elevated ureteral opening pressure was 100% predictive of obstruction and may obviate the need for more elaborate pressure-flow analyses. However, if the ureteral pelvic pressure remained low, the possibility of a potentially significant obstruction could not be definitively eliminated and further evaluation was required.