URETERAL OPENING PRESSURE - A NOVEL PARAMETER FOR THE EVALUATION OF PEDIATRIC HYDRONEPHROSIS

Purpose: The antegrade nephrostogram is an important tool in the evalu ation of the upper urinary tract. However, the information currently p rovided by a nephrostogram is largely limited to anatomical details. T o establish a meaningful pressure-flow parameter that may be incorpora ted into a routine nephrostogram, we evaluated the ureteral opening pr essure (defined as the pressure at which contrast material is first se en beyond the suspected site of obstruction) and correlated these find ings with the results of pressure-flow studies performed with an exter nal 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 (Soc iety of Fetal Urology classification) and patient age range was 0.2 to 12 years (median 1.1). The suspected sites of obstruction were the ur eteropelvic and ureterovesical junctions in 42 and 10 renal units, res pectively. With the patient under general anesthesia 22 gauge percutan eous nephrostomy needles were inserted. Pressure-flow studies with an external infusion and/or furosemide induced diuresis were then perform ed. As the renal pelvic pressure progressively increased during the co urse of the pressure-flow studies, the renal pelvic pressure at which contrast material was first seen to appear distal to the suspected sit e of obstruction was recorded as the ureteral opening pressure. Ureter al opening pressures were compared to the results of the pressure-flow studies. Results: With a positive test defined as renal pelvic pressu re greater than 14 cm. water, positive ureteral opening pressures were associated with positive pressure-flow study results in 100% of the c ases, regardless of which form of pressure-flow study was used or wher e 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 s tudy and the suspected site of obstruction. Conclusions: An elevated u reteral opening pressure was 100% predictive of obstruction and may ob viate the need for more elaborate pressure-flow analyses. However, if the ureteral pelvic pressure remained low, the possibility of a potent ially significant obstruction could not be definitively eliminated and further evaluation was required.