Obstructive uropathies and antenatal hydro­nephrosis

Objectives

After this topic you will be able to

• Classify antenatal and postnatal urinary tract dilation using the UTD system.
• Choose the right timing for the first postnatal ultrasound.
• Know the indications for VCUG, MAG3/DTPA and antibiotic prophylaxis.
• Recognize suspected posterior urethral valves and know the urgent measures.
• Explain the indications for surgery in UPJ obstruction, megaureter and ureterocele.
• Know the screening timing in fetal urology, the multidisciplinary approach and the narrow indications for fetal intervention.

Basics

Antenatal hydronephrosis in numbers

• 1–4.5%of pregnancies
• ~50% or moretransient, physiological dilation
• 10–30%UPJ obstruction
• 10–20%vesicoureteral reflux

Other causes: megaureter (5–10%), multicystic dysplastic kidney, duplex collecting system, ureterocele, ectopic ureter, and the rare but most severe cause, posterior urethral valves (1–2%).

There is a direct relationship between the degree of dilation and the likelihood of pathology: as the grade increases, the likelihood of persistent pathology and surgery rises.

Basics

UTD classification: antenatal

APD: anteroposterior diameter of the renal pelvis. Regardless of the measurement, the finding is classified as A2–3 if there is peripheral calyceal dilation, ureteral dilation, parenchymal abnormality, a bladder abnormality or unexplained oligohydramnios.

Basics

UTD classification: postnatal

This site uses UTD as a unified language. According to EAU 2026, no single grading system (UTD, SFU, APD) is superior, so besides the APD value the report should describe the calyces, ureter, parenchyma and bladder, and the findings should be integrated.

Basics

Posterior urethral valves (PUV)

A congenital membrane in the posterior urethra in boys. It occurs in about one in 5,000–8,000 boys and is the main obstructive cause of chronic kidney disease in children.

• Antenatal signs: bilateral hydroureteronephrosis, a large thick-walled bladder, the "keyhole" sign, oligohydramnios.
• Postnatal signs: weak or dribbling stream, straining, palpable bladder, urinary tract infection, sepsis, renal failure.

Basics

Fetal urology (EAU 2026, new chapter)

• Screening: ultrasound in the first (11–14 weeks) and second (17–22 weeks) trimesters to assess urinary tract malformations (strong).
• Multidisciplinary team: maternal-fetal medicine, clinical genetics, pediatric urology and nephrology, neonatology, psychology (strong).
• Fetal urine biochemistry: via serial vesicocenteses (weak).
• Before intervention in lower urinary tract obstruction, exclude life-limiting genetic and structural anomalies (weak).
• Fetal intervention (e.g. vesicoamniotic shunt) can be considered with signs of obstruction and reduced amniotic fluid in the second trimester (weak).

Diagnosis

When should the first postnatal ultrasound be done?

1. Unilateral, A1 or A2–3: first ultrasound more than 48 hours after birth, within the first month. In the first two days, physiological dehydration can mask the dilation.
2. Severe cases: bilateral dilation, solitary kidney, oligohydramnios, suspected PUV (boy, thick-walled bladder): ultrasound immediately after birth, in the maternity hospital (EAU 2026).
3. Even if the first ultrasound is normal, in A2–3 cases a repeat ultrasound is done after 4–6 weeks.
4. Further work-up: serial ultrasound, then diuretic renography, and VCUG in some cases (strong).

Diagnosis

Who needs a VCUG?

The voiding cystourethrogram (VCUG) shows vesicoureteral reflux and the urethra (PUV).

• Suspected PUV: urgently, in the first days.
• UTD P3 and most P2 cases, especially with ureteral dilation, bilateral dilation, a duplex system or ureterocele.
• Bladder abnormality.
• An infant with hydronephrosis who has had a febrile urinary tract infection.

In isolated UTD P1, VCUG is not routinely recommended.

Diagnosis

MAG3/DTPA scintigraphy

MAG3/DTPA diuretic renography shows the functional impact of obstruction: the separate function of each kidney (split function) and drainage after a diuretic.

• Timing: after 4–6 weeks of life, to allow renal maturation, under standardized conditions (hydration, furosemide timing, bladder drainage).
• Indication: P2–P3 cases, suspected UPJ obstruction or obstructive megaureter.
• The key parameter is split function: below 40% or a decrease of more than 10 percentage points on repeat studies is significant.
• A prolonged T½ is associated with a higher likelihood of surgery, but in children the drainage curve alone is not proof of obstruction; the result is interpreted together with the ultrasound trend.

DMSA scintigraphy shows scarring and dysplasia, not obstruction. It is used to confirm the absence of function in a multicystic kidney.

Diagnosis

Urgent measures when PUV is suspected

1. Bladder drainage: a small catheter (usually a 5–8 Fr feeding tube). A Foley balloon can irritate the bladder neck.
2. Creatinine, electrolytes, acid-base status. Maternal creatinine affects the infant's value in the first days, so the trend matters.
3. Be prepared for post-obstructive diuresis: fluid and electrolyte balance.
4. If there is a urinary tract infection, intravenous antibiotics.
5. Confirmation of the diagnosis by VCUG, then endoscopic valve ablation once the infant is stable.

Treatment

Follow-up and antibiotic prophylaxis

Antibiotic prophylaxis: not routinely recommended in asymptomatic UPJ obstruction. It may be offered to high-risk groups: uncircumcised infants, hydroureteronephrosis, high-grade hydronephrosis (weak). In megaureter, prophylaxis is recommended in the first year of life; a ureter of 7 mm or more means a higher UTI risk. In reflux, the decision is made separately.

Treatment

UPJ obstruction

Most cases of hydronephrosis are followed without loss of renal function and improve over time. Indications for surgery (EAU 2026):

• Symptoms: recurrent flank pain (intermittent pain episodes in adolescents), febrile urinary tract infection; also stones.
• Split function below 40% or a decrease of more than 10 percentage points on follow-up studies.
• Poor drainage after furosemide.
• Increasing APD on ultrasound, high-grade (SFU III–IV) dilation, parenchymal thinning.
• Severe bilateral dilation or severe dilation in a solitary kidney.

The decision is based on the time course of the hydronephrosis and of renal function (weak). Pyeloplasty is done when the obstruction is confirmed clinically or by serial imaging.

The standard operation is Anderson-Hynes pyeloplasty (open, laparoscopic or robot-assisted). The success rate is about 90–95%. After surgery, follow-up is done with ultrasound and, if needed, MAG3/DTPA.

Treatment

Megaureter, ureterocele, MCDK

Treatment

After valves: lifelong follow-up

• Within 2–3 months after valve ablation, a control VCUG or cystoscopy, and assessment of flow and post-void residual.
• Renal function, blood pressure, proteinuria, growth: regularly.
• Bladder function: a "valve bladder" may present with high pressure, nocturnal polyuria and incomplete emptying; if needed, urodynamics, anticholinergics, catheterization, overnight drainage.
• Planned transition to adult urology and nephrology in adolescence.