Is a 13 mm anteroposterior diameter (APD) in the left kidney of a 10-year-old boy problematic?

Assessment of 13 mm APD in Left Kidney of a 10-Year-Old Boy

A 13 mm anteroposterior diameter (APD) in the left kidney of a 10-year-old boy is not typically problematic and likely represents mild hydronephrosis that warrants follow-up ultrasound in 3-6 months but does not require immediate intervention. 1

Classification and Significance

The finding of a 13 mm APD falls into the category of mild to moderate hydronephrosis according to current classification systems:

• According to the Urinary Tract Dilation (UTD) classification system, this measurement likely represents UTD P1 (mild postnatal dilation) 1
• In the Society for Fetal Urology (SFU) system, this would be approximately grade 2-3 1

Clinical Implications

Risk Assessment

• Isolated APD of 13 mm without other abnormal findings has a favorable prognosis
• Most cases of mild to moderate hydronephrosis (UTD P1) resolve spontaneously by 24-48 months of age 1
• Resolution occurs in approximately 90% of UTD P1 patients by 48 months 1

Recommended Follow-up

1. Imaging follow-up:

   • Repeat renal ultrasound in 3-6 months to assess for stability or resolution 1
   • A minimum of 2 postnatal ultrasounds should be obtained prior to discontinuation of surveillance 1
   • If initial follow-up shows improvement, continue monitoring until complete resolution

2. No immediate need for:

   • Voiding cystourethrogram (VCUG)
   • Renal functional imaging (MAG3 scan)
   • Antibiotic prophylaxis

Key Considerations

When to Consider Additional Evaluation

Additional evaluation should be considered if:

• APD increases on follow-up imaging
• Other abnormal findings develop:
  • Parenchymal thinning
  • Calyceal dilation
  • Ureteral dilation
  • Bladder abnormalities
• Development of symptoms:
  • Urinary tract infection
  • Flank pain
  • Hematuria

Important Distinctions

It's important to differentiate isolated hydronephrosis from other conditions:

• Isolated hematuria: If the child has hematuria without pain or trauma, this finding would require a different approach. In such cases, ultrasound would be appropriate to evaluate for structural abnormalities 1

• Autosomal dominant polycystic kidney disease (ADPKD): This finding is not consistent with ADPKD, which typically presents with multiple cysts rather than hydronephrosis 1

Conclusion

A 13 mm APD in the left kidney of a 10-year-old boy represents mild to moderate hydronephrosis that should be monitored with follow-up ultrasound in 3-6 months. The prognosis is generally excellent, with most cases resolving spontaneously. No immediate intervention is required unless there are additional concerning findings or symptoms develop.