Surgical intervention is decided based on evidence of obstruction and depends upon T1/2 of time activity curve (T1/2 >20 minutes), decreased renal function (<40% differential renal function), deteriorating function (>5% change on consecutive renal scans), or worsening drainage on serial imaging. Tc-99m MAG3 renal scan can be used to monitor function over time, with a decrease in differential renal function on the affected side often serving as an indicator of a need for intervention [55,73]. MRI Abdomen and Pelvis There is no consensus on the role of MRU, performed without and with IV contrast, in patients with moderate to severe postnatal hydronephrosis especially before VCUG is performed. Although MRU is not routinely recommended in the initial workup of antenatal hydronephrosis, some authors have argued that it can add value through improved anatomical imaging, for example, in the evaluation of hydronephrosis in the setting of atypical urinary tract anatomy, such as certain duplicated collecting systems or renal dysgenesis [74]. MRU can also adequately assess degree of obstruction [75]. One potential limitation of MRU is inaccurate estimation of split renal function compared with renal scan in kidneys with severely diminished renal function [75] and kidneys with severe hydronephrosis [76]. should be considered [6,29,53,77]. Of the causes of hydronephrosis, UPJO accounts for approximately 10% to 65% of cases and in 90% of cases the obstruction is unilateral [2,4,22,48]. As the severity of hydronephrosis increases, the risk of UPJO also increases, and as much as 35% of significant hydronephrosis (>10 mm APRPD postnatally) was attributable to UPJO in one study. Lee et al [51] showed a 54% risk of UPJO in severe (>15 mm APRPD postnatally) urinary tract dilation. Even in the setting of abnormal findings on initial neonatal US, further follow- up US between 1 and 6 months may be useful to re-evaluate a dilated urinary tract after bladder catheterization [1,21,23,53-55].
Antenatal Hydronephrosis Infant. Surgical intervention is decided based on evidence of obstruction and depends upon T1/2 of time activity curve (T1/2 >20 minutes), decreased renal function (<40% differential renal function), deteriorating function (>5% change on consecutive renal scans), or worsening drainage on serial imaging. Tc-99m MAG3 renal scan can be used to monitor function over time, with a decrease in differential renal function on the affected side often serving as an indicator of a need for intervention [55,73]. MRI Abdomen and Pelvis There is no consensus on the role of MRU, performed without and with IV contrast, in patients with moderate to severe postnatal hydronephrosis especially before VCUG is performed. Although MRU is not routinely recommended in the initial workup of antenatal hydronephrosis, some authors have argued that it can add value through improved anatomical imaging, for example, in the evaluation of hydronephrosis in the setting of atypical urinary tract anatomy, such as certain duplicated collecting systems or renal dysgenesis [74]. MRU can also adequately assess degree of obstruction [75]. One potential limitation of MRU is inaccurate estimation of split renal function compared with renal scan in kidneys with severely diminished renal function [75] and kidneys with severe hydronephrosis [76]. should be considered [6,29,53,77]. Of the causes of hydronephrosis, UPJO accounts for approximately 10% to 65% of cases and in 90% of cases the obstruction is unilateral [2,4,22,48]. As the severity of hydronephrosis increases, the risk of UPJO also increases, and as much as 35% of significant hydronephrosis (>10 mm APRPD postnatally) was attributable to UPJO in one study. Lee et al [51] showed a 54% risk of UPJO in severe (>15 mm APRPD postnatally) urinary tract dilation. Even in the setting of abnormal findings on initial neonatal US, further follow- up US between 1 and 6 months may be useful to re-evaluate a dilated urinary tract after bladder catheterization [1,21,23,53-55].