Nuclear techniques in the diagnosis and management of pediatric obstructive uropathy

1022 Obstructive uropathy is a common clinical problem in the pediatric population. The clinical presentation is often that of hydronephrosis which requires an evaluation for the presence of excretory obstruction. Common locations of excretory obstruction are at the ureteropelvic junction and at the ureterovesical junction. Diuretic urography is used for this evaluation. Tc-99m MAG3 is primarily excreted by tubular secretion and Tc-99m DTPA is excreted by glomerular filtration, but either agent can be used for the evaluation. When the renal pelvis is full with tracer the diuretic furosemide is given. If there is prompt clearance of tracer, obstructive uropathy is excluded, but if tracer does not clear then obstruction is diagnosed. Clearance of tracer starts 5 to 15 minute from the time of tracer injection. With normal renal function, a clearance half time of less than 10 minutes is normal. Factors other than excretory obstruction that may cause a delay in clearance are a large hydronephrosis or impaired renal function. These other factors therefore need to be taken into consideration in the evaluation of a prolonged clearance half time. Diuretic renography can be used not only to diagnose the presence of obstruction but also to reevaluate the patient after surgical intervention. Examples are provided of renographic evaluation of hydronephrosis with diagnosis of obstructive uropathy and reevaluation after surgical correction.