Fetal Hydronephrosis

Key Concepts

• Most common prenatally diagnosed urologic abnormality
• Affects 1-5% of all pregnancies
• Defined as dilation of renal collecting system
• Can be unilateral or bilateral
• May represent physiologic or pathologic process

Etiology

• Physiologic (50-70%):
  • Transient hydronephrosis
  • Normal variant
• Pathologic (30-50%):
  • Ureteropelvic junction obstruction (UPJO)
  • Vesicoureteral reflux (VUR)
  • Ureterovesical junction obstruction
  • Posterior urethral valves (PUV)
  • Ureterocele
  • Primary megaureter

Prenatal Diagnosis

Ultrasound Parameters

• Anterior-Posterior Renal Pelvic Diameter (APRPD):
  • Second trimester: >4mm
  • Third trimester: >7mm
• Society for Fetal Urology (SFU) Grading:
  • Grade 0: No dilation
  • Grade 1: Only renal pelvis visible
  • Grade 2: Few calices visible
  • Grade 3: All calices visible
  • Grade 4: Parenchymal thinning

Additional Imaging Findings

• Calyceal dilation
• Parenchymal thickness
• Ureteral dilation
• Bladder abnormalities
• Amniotic fluid volume
• Contralateral kidney status

Postnatal Assessment

Initial Evaluation

• Timing:
  • Severe cases: 24-48 hours of life
  • Mild-moderate cases: 1-2 weeks of life
• Physical Examination:
  • Abdominal masses
  • Bladder distension
  • External genitalia abnormalities
  • Associated anomalies

Imaging Studies

• Renal Ultrasound:
  • First-line imaging
  • Bilateral kidney assessment
  • Bladder evaluation
  • Ureteral status
• Voiding Cystourethrogram (VCUG):
  • Indicated for:
    • Bilateral hydronephrosis
    • Ureter dilation
    • Bladder abnormalities
    • Male infants with severe hydronephrosis
• Nuclear Renal Scan:
  • MAG3 or DTPA
  • Assesses:
    • Differential renal function
    • Drainage patterns
    • Obstruction

Laboratory Studies

• Serum:
  • Creatinine
  • Electrolytes
  • BUN
• Urinalysis and culture
• Genetic testing if indicated

Treatment Approaches

Conservative Management

• Indications:
  • Mild-moderate hydronephrosis
  • Normal differential function
  • No obstruction
• Monitoring:
  • Serial ultrasounds
  • Growth assessment
  • UTI surveillance

Antibiotic Prophylaxis

• Indications:
  • High-grade hydronephrosis
  • Suspected VUR
  • Ureterocele
  • PUV
• Options:
  • Amoxicillin
  • Trimethoprim-sulfamethoxazole (>2 months)

Surgical Intervention

• Indications:
  • Worsening hydronephrosis
  • Decreased function
  • Recurrent infections
  • Specific anatomic abnormalities
• Procedures:
  • Pyeloplasty for UPJO
  • Ureteral reimplantation for VUR
  • Valve ablation for PUV
  • Ureterocele incision

Prognosis and Follow-up

Monitoring Schedule

• Mild Cases:
  • Ultrasound every 3-6 months
  • Resolution often by age 2
• Moderate-Severe Cases:
  • More frequent imaging
  • Regular renal function assessment
  • Growth monitoring

Long-term Outcomes

• Resolution Rates:
  • Mild: 80-90%
  • Moderate: 50-70%
  • Severe: Variable based on etiology
• Complications:
  • Chronic kidney disease
  • Recurrent UTIs
  • Hypertension
  • Growth issues

Quality of Life Considerations

• Regular medical follow-up
• Impact on family dynamics
• Need for surgical interventions
• Long-term renal health monitoring