With the increasing use of sonography, dilatation of the pelvicalyceal system (hydronephrosis, HN) or ureter (hydroureteronephrosis, HUN) is the most common abnormality of the urinary tract detected in utero or after birth. Common causes of congenital HN and HUN include vesicoureteric reflux (VUR), ureteropelvic junction (UPJ) stenosis, ureterovesical junction (UVJ) stenosis, posterior urethral valve (PUV), ectopic ureter with or without duplication, ectopic ureterocele, and primary nonobstructive dilatation. Some of the affected children present with urinary tract infection or an abdominal mass, but most of them remain asymptomatic for a long time. The natural course of HN/HUN in infants and children is variable. In some patients, HN/HUNimproves or resolves completely, butin others, it remains stable or gradually gets worse and, depending on the underlying cause and withouttimely surgicalintervention, may resultin silent loss of renal function or recurrent episodes of abdominal/flank pain. Therefore, the aim for imaging evaluation of these infants and children should be to identify the kidneys that are at risk for loss of function and prevent loss of function by timely surgical intervention.
Conventional dynamic renal scintigraphy provides information about the function of the affected kidney and supplements the ultrasound findings. Diuresis renography is a safe and widely available provocative test that, in addition to evaluating the renal function, allows evaluation of the extent and pattern of clearance of the radiopharmaceutical from the dilated urinary tract under high diuresis (1,2). The results of diuresis renography are dependent on several physiologic, anatomic, mechanical, and technical factors, including function of the affected kidney, capacity and compliance of the dilated system, the patient’s hydration status, fullness of the bladder, dose of furosemide, time of injection of furosemide relative to injection of the radiopharmaceutical, and selection of regions of interest for generation of time–activity curves. Understanding the principles of the test, its limitations, and the sources of error is essential in the interpretation of the results and effective use of the test.