Is intervention recommended for patients with significant hydronephrosis and parenchymal thinning?

Management of Hydronephrosis with Parenchymal Thinning

Surgical intervention is indicated for patients with significant hydronephrosis and parenchymal thinning when there is evidence of decreased renal function (<40% differential renal function), deteriorating function (>5% change on consecutive renal scans), or worsening drainage on serial imaging. 1

Diagnostic Evaluation

• Initial assessment should include renal ultrasound to confirm hydronephrosis severity, evaluate renal parenchymal thickness, and assess for hydroureter or other urinary tract abnormalities 2
• MAG3 renal scan is preferred over DTPA scan for evaluating split renal function and degree of obstruction due to its higher extraction fraction (40-50%) and better image quality in patients with impaired renal function 1
• The Society for Fetal Urology (SFU) grading system (grades 1-4) or Anterior-posterior renal pelvic diameter (APRPD) measurement should be used to grade hydronephrosis severity 1, 2

Decision Criteria for Intervention

• Surgical intervention is warranted when any of these criteria are met:

  • T1/2 of time activity curve >20 minutes on diuretic renal scan 1
  • Decreased renal function (<40% differential renal function) 1
  • Deteriorating function (>5% change on consecutive renal scans) 1
  • Worsening drainage on serial imaging 1

• Parenchymal thinning pattern significantly impacts renal function:

  • Grade IVB hydronephrosis (diffuse cortical thinning) is associated with worse renal function (66% have <40% differential function) 3
  • Grade IVA hydronephrosis (segmental cortical thinning) has better function (only 24% have <40% differential function) 3

Special Considerations

• Even kidneys with severely impaired function (<10% split function) may show significant improvement after pyeloplasty, challenging the traditional recommendation for nephrectomy in these cases 4
• Children with severe hydronephrosis, increased kidney size, and parenchymal thinning require closer follow-up due to higher risk of urinary tract infections (30.6% vs 12.2% in mild hydronephrosis) 5
• The Hydronephrosis Severity Score (HSS), which combines ultrasonographic and renographic parameters, can help predict which patients will require surgery - those with HSS ≥9 typically need intervention 6

Post-Intervention Monitoring

• Follow-up should include ultrasound at 1-6 months post-procedure and MAG3 renal scan to evaluate improvement in drainage and function 2
• For complex cases with severe dilatation and parenchymal thinning, additional surgical techniques like renal folding (Y-plasty) may be necessary to create a dependent ureteropelvic junction and prevent secondary obstruction 7

Pitfalls and Caveats

• Relying solely on ultrasound findings without functional assessment can lead to inappropriate management decisions 1
• MRI urography may provide inaccurate estimation of split renal function compared to renal scan in kidneys with severely diminished function or severe hydronephrosis 1
• Waiting too long for intervention in cases with diffuse parenchymal thinning (Grade IVB) may lead to irreversible loss of renal function 3
• Younger infants (aged 2-5 months) with higher pre-operative differential renal function show better recovery after surgical intervention 6