Surgical intervention is decided based on evidence of obstruction based on 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 [55,73]. 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. 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 that there are systematic differences in estimation of split renal function compared with renal scan in kidneys with severely diminished renal function and kidneys with severe hydronephrosis [76]. Supporting Documents The evidence table, literature search, and appendix for this topic are available at https://acsearch. acr.org/list. The appendix includes the strength of evidence assessment and the final rating round tabulations for each recommendation. For additional information on the Appropriateness Criteria methodology and other supporting documents go to www. acr.org/ac. Appropriateness Category Names and Definitions Relative Radiation Level Information Potential adverse health effects associated with radiation exposure are an important factor to consider when selecting the appropriate imaging procedure.
Antenatal Hydronephrosis Infant. Surgical intervention is decided based on evidence of obstruction based on 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 [55,73]. 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. 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 that there are systematic differences in estimation of split renal function compared with renal scan in kidneys with severely diminished renal function and kidneys with severe hydronephrosis [76]. Supporting Documents The evidence table, literature search, and appendix for this topic are available at https://acsearch. acr.org/list. The appendix includes the strength of evidence assessment and the final rating round tabulations for each recommendation. For additional information on the Appropriateness Criteria methodology and other supporting documents go to www. acr.org/ac. Appropriateness Category Names and Definitions Relative Radiation Level Information Potential adverse health effects associated with radiation exposure are an important factor to consider when selecting the appropriate imaging procedure.