Disease Description (Causes and Symptoms)
- Definition: Congenital hydronephrosis is a condition in which the renal pelvis and calyces (pelvis and calyces) become abnormally dilated due to obstruction of the urinary outflow tract or vesicoureteral reflux. It is the most commonly detected urinary tract abnormality on prenatal ultrasound.
- Main causes: Ureteropelvic junction (UPJ) obstruction, vesicoureteral reflux (VUR), ureteral stenosis (including megaureter), posterior urethral valves (POV), duplicated ureters, polycystic or dysplastic kidneys (polycystic kidney disease, cystic dysplasia, etc.), non-obstructive megaureter, and others.
- Pathophysiology summary: When urinary outflow is obstructed, pressure within the renal pelvis rises, causing dilation of the renal pelvis and calyces. If this persists, the renal parenchyma may be compressed, leading to atrophy and impaired function. Fetuses produce more urine than after birth and have more elastic urinary tracts, so transient (physiologic) dilation must be distinguished from pathological dilation.
- Clinical symptoms: Most cases are asymptomatic (especially unilateral). Bilateral or severe obstruction may cause uremia (symptoms of renal failure), and if infection is present, pyonephrosis (fever, weakness, etc.) may occur. It is often discovered on prenatal ultrasound.
Treatment
- General principles: Observation is appropriate in many cases (most resolve spontaneously within the first year of life). If pathological obstruction or impaired function is confirmed, appropriate intervention (medication, procedures, or surgery) should be considered.
- Diagnostic and follow-up tests and timing (standard approach)
- When prenatal hydronephrosis is identified: Perform a renal ultrasound after 72 hours of age (to assess neonatal kidney size and the degree of dilation).
- If dilation of the renal pelvis or ureter persists, or ureteral dilation is seen: Perform a voiding cystourethrogram (VCUG) at approximately 2–6 weeks of age to evaluate for vesicoureteral reflux and posterior urethral valves.
- If there is no reflux and evaluation of obstruction and differential renal function is needed: Perform a diuretic renal scan (MAG3, etc.) at approximately 4–8 weeks to assess function and drainage.
- Conservative treatment
- Periodic ultrasound follow-up (changes in size and renal parenchymal thickness) and infection prevention (low-dose prophylactic antibiotics when necessary).
- Appropriate antibiotic treatment and culture-based treatment when infection occurs.
- Surgical treatment (indications)
- When severe bilateral obstruction is present and renal function needs to be preserved (risk of renal failure).
- When renal parenchymal atrophy due to hydronephrosis (decreased renal function) is present, or when function of one kidney has decreased to 40% or less.
- Recurrent or uncontrolled urinary tract infections (not controlled with prophylactic antibiotics).
- Examples of surgery: Pyeloplasty for UPJ obstruction; ureteral reimplantation for VUR (or combined treatment depending on severity); and endoscopic posterior urethral valve resection (ablation) for posterior urethral valves.
- Fetal (prenatal) treatment
- Procedures such as shunting (connecting the amniotic cavity and the renal pelvis) may be performed in very limited indications to preserve renal function, but they are used selectively because of the high risk of complications and failure.
- Long-term follow-up: Even after surgery, decreased renal function, hypertension, and proteinuria may develop during growth, so long-term follow-up from childhood through adulthood is recommended.
- Lifestyle management and precautions
- Prevent urinary tract infections (maintain cleanliness, establish appropriate urination habits, and use prophylactic antibiotics when necessary), and be cautious of worsening renal function during dehydration or high fever. Consult the treating physician when using nephrotoxic medications (e.g., high-dose nonsteroidal anti-inflammatory drugs, aminoglycosides, etc.).
Outpatient Visit Checklist (Including Items to Bring / Example Questions)
- Items to bring (helpful for consultation and assessment)
- Prenatal ultrasound findings and delivery records (condition at birth, Apgar score, etc.).
- Previous renal ultrasound results (images or reports if possible), and the results and dates of all imaging tests, including VCUG and renal scans (MAG3).
- Previous urine culture results (history of UTI and medications used for treatment), and records of recent temperature and symptom changes (fever, decreased feeding, abnormal urination, etc.).
- List of currently used medications and allergies, and family history (kidney disease, urinary tract abnormalities, etc.).
- Information to tell the doctor in advance during the outpatient visit
- It is useful to have records of the renal pelvic dilation (antero-posterior diameter) measurement or the ultrasound assessment (mild, moderate, or severe).
- Any recent changes in urine volume, urination frequency or pattern, fever, vomiting, or other symptoms.
Examples of General Questions to Ask the Doctor
- "How is the severity of my child's hydronephrosis (mild/moderate/severe) assessed?"
- "What is the schedule for follow-up tests, and which tests are needed?"
- "Is surgery necessary, and if so, when should it be performed?"
- "What is the prognosis, and what can parents do to help protect renal function?"
- "Is prophylactic antibiotic therapy needed? What are the side effects of taking antibiotics long term?"
Examples of Disease-Specific Questions
- "The renal pelvic AP diameter on the ultrasound is X mm (enter the value from the report). Based on this measurement, is observation alone safe, or are VCUG or a renal scan needed right away?"
- "The differential renal function on the MAG3 (or DMSA) scan was Y%. How do you recommend assessing the surgical indication (e.g., less than 40%) and treatment options?"
(Summary) Congenital hydronephrosis is commonly detected on prenatal and neonatal ultrasound, and most cases improve spontaneously. However, some cases require active diagnosis and treatment (VCUG, renal scan, or surgery) because of impaired function or infection. Refer to the schedule for early postnatal testing (ultrasound at 72 hours → VCUG at 2–6 weeks if needed → renal scan at 4–8 weeks), and remember that long-term monitoring of renal function and infection prevention are important.