What are the causes and treatment options for left hydronephrosis in newborns?

Left Hydronephrosis in Newborns: Causes and Treatment

Ultrasound evaluation after 48-72 hours of life is the cornerstone of initial assessment for newborns with left hydronephrosis, followed by appropriate imaging studies based on severity to determine the underlying cause and guide management. 1

Causes of Left Hydronephrosis in Newborns

Left-sided hydronephrosis is more common than right-sided and occurs more frequently in males. The main causes include:

1. Ureteropelvic Junction Obstruction (UPJO) - Accounts for approximately 32.8% of cases 2

   • Characterized by narrowing at the junction between renal pelvis and ureter
   • More common on the left side

2. Vesicoureteral Reflux (VUR) - Accounts for about 40.2% of cases 2

   • Retrograde flow of urine from bladder to kidney
   • Occurs in approximately 16% of infants with antenatal hydronephrosis 1

3. Posterior Urethral Valves (PUV) - Accounts for 13.4% of cases 2

   • Obstructive membrane in the posterior urethra
   • More common in male infants
   • Presents with bilateral hydronephrosis, bladder wall thickening

4. Transient Hydronephrosis - Accounts for 13.4% of cases 2

   • Temporary dilation that resolves spontaneously
   • Most common in mild to moderate cases

5. Primary Megaureter - Accounts for 5-10% of cases 1

   • Persistent ureteral dilation (>7 mm)
   • May be obstructive, refluxing, or non-obstructive/non-refluxing

Diagnostic Approach

Initial Evaluation

• Renal Ultrasound (US): Should be performed 48-72 hours after birth (not earlier due to low urine production in newborns) 1
  • Exceptions: severe bilateral hydronephrosis, bladder abnormalities, oligohydramnios
  • Assesses severity using Society for Fetal Urology (SFU) grading or anteroposterior renal pelvic diameter (APRPD)

Follow-up Based on Severity

1. Mild Hydronephrosis (SFU grade 1-2):

   • Follow-up US in 1-6 months 1
   • Low risk of underlying anatomic abnormality

2. Moderate to Severe Hydronephrosis (SFU grade 3-4 or APRPD >15 mm):

   • Follow-up US in 1-6 months
   • Consider VCUG (voiding cystourethrography) to rule out VUR
   • Consider MAG3 renal scan (at 2+ months of age) to assess function and obstruction 1

3. Special Considerations:

   • Male infants with moderate/severe hydronephrosis: VCUG to exclude PUV 1
   • Suspected obstruction: MAG3 renal scan preferred over DTPA due to better extraction fraction (40-50% vs 20%) 1

Treatment Approach

Conservative Management

• Observation: Appropriate for most cases of mild to moderate hydronephrosis

  • 65-69% of severe unilateral hydronephrosis resolves spontaneously 3
  • Mean time to maximum improvement: 2.5 years 3
  • Regular ultrasound follow-up required

• Antibiotic Prophylaxis: Consider for:

  • Moderate to severe hydronephrosis
  • Diagnosed VUR
  • Although controversial, may reduce UTI risk 1

Surgical Intervention

• Indications for Surgery (approximately 22% of cases require intervention) 3:

  • Progressive hydronephrosis
  • Declining differential renal function (<40%)
  • Recurrent UTIs
  • Symptoms (pain, hematuria)

• Surgical Options:

  • Pyeloplasty: For UPJO
    • Most commonly needed before 18 months of age 3
    • Restores function to pre-deterioration levels when performed promptly
  • Valve Ablation: For PUV
  • Ureteral Reimplantation: For severe VUR or obstructive megaureter

Monitoring and Follow-up

• Close follow-up especially during first 2 years is essential 3
• Serial ultrasounds to monitor hydronephrosis
• Repeat functional studies (MAG3) if worsening hydronephrosis

Important Caveats

1. Prolonged half-time on renal scan or high-grade hydronephrosis alone is not an absolute indicator for surgery in infants 3

2. Left-sided hydronephrosis may be more difficult to assess accurately on ultrasound due to anatomical factors 4

3. Differential renal function may initially be normal even in obstructive cases, making early diagnosis challenging 5

4. Approximately 49.2% of patients with any degree of hydronephrosis may develop complications (UTI, renal insufficiency) or require surgery 2

5. Associated abnormalities occur in approximately 22.4% of patients with hydronephrosis 2