Bruce J. Schlomer, MD
Laurence S. Baskin, MD, FACS, FAAP
BASICS
DESCRIPTION
• In utero dilation of fet al renal collecting system
• May represent a normal developmental variant or a pathologic anomaly
• Prenatal hydronephrosis (PN) may be observed early in pregnancy but the diagnosis usually cannot be made with certainty until 18wk of gestation
• Severity based on anterior–posterior renal pelvis diameter (APD) (1)
– Mild: 4 to <7 mm (2nd trimester); 7 to <9 mm (3rd trimester)
– Moderate: 7 to ≤10 mm (2nd trimester); 9 to ≤15 mm (3rd trimester)
– Severe: >10 mm (2nd trimester); >15 mm (3rd trimester)
EPIDEMIOLOGY
Incidence
• 1–5% of fetuses are observed to have PN (2)
– Mild: 57–88%
– Moderate: 10–30%
– Severe: 2–13%
• Risk of clinically significant PN increases with severity. Risk of undergoing surgery <10% with mild and >50% with severe.
Prevalence
None
RISK FACTORS
• Family history of renal abnormalities or vesicoureteral reflux
• Previous fet al loss due to urinary tract causes
Genetics
None
PATHOPHYSIOLOGY
• Transient hydronephrosis (most common, physiologic dilation of the ureter is seen in 41–88% of cases of PN)
– ∼90% of mild PN will be transient
• Ureteropelvic junction (UPJ) obstruction (most common pathophysiology)
• Ureterovesical obstruction (megaureter, obstructed and nonobstructed)
• Bladder outlet obstruction (posterior urethral valves (PUVs), urethral atresia)
• Nonobstructive processes: Vesicoureteral reflux, nonrefluxing nonobstructed megaureter, and prune belly syndrome
• Severe PN with oligohydramnios may cause pulmonary hypoplasia
ASSOCIATED CONDITIONS
Congenital hydronephrosis is associated with many syndromes.
GENERAL PREVENTION
None
DIAGNOSIS
HISTORY
• Timing of prenatal detection; earlier detection implies more severe condition.
• Presence of calyectasis and renal cortical thinning indicate more severe condition.
• Presence of cortical cysts may indicate dysplasia.
• Unilateral vs. bilateral renal involvement is a critical determination for diagnosis and prognosis.
• Change in dilation in relation to bladder filling may indicate vesicoureteral reflux.
• Presence of oligohydramnios important: Suggests severe comprise of renal function.
– Associated with severe obstructive uropathy due to PUVs, congenital urethral stricture, or ureterocele obstructing bladder outlet
– Associated with pulmonary hypoplasia and fet al or neonatal death
PHYSICAL EXAM
N/A
DIAGNOSTIC TESTS & INTERPRETATION
Lab
• Maternal α-feto protein may be elevated in some cases of fet al renal anomalies
• Assessment of pulmonary maturity in patients with oligohydramnios (lecithin-to-sphingomyelin ratio)
• Amniotic fluid studies:
– Volume: Composed mostly (90%) of fet al urine after the 16th wk of gestation
– Correlates with fet al renal function
• Fet al karyotype (may indicate gender or important genetic information)
• Assessment of fet al urinary electrolytes:
– Generally only done with oligohydramnios
– Good prognosis: Sodium <100 mg/dL; osmolarity <210 mOsmol/dL; chloride <90 mg/dL (remember dilute urine is better in the fetus)
• Postnatal serum electrolyte assessment:
– Nadir creatinine (<0.7 mg/dL in 1st yr holds good prognosis)
– CO2: Acidosis has a poor prognosis.
• Urinalysis and urine culture as needed
Imaging
• Prenatal US in 3rd trimester: Based upon severity of PN in 2nd trimester(1)
– Mild: Consider 3rd trimester US
– Moderate: 3rd trimester US
– Severe: US in 3–4 wk
• Additional prenatal US in 3rd trimester: Based upon severity of PN in 3rd trimester (1)
– Mild: Postnatal evaluation
– Moderate: Postnatal evaluation
– Severe: US in 2–3 wk
• Postnatal evaluation: Controversial. Society of Fet al Urology (SFU) recommendations based on severity of PN (1)
• Unilateral mild PN
– Postnatal US at 2–4 wk
– Consider VCUG at 2–4 wk if hydro present on postnatal US
– Consider diuretic nuclear renal scan (MAG-3) at 4 wk if hydro present on postnatal US
• Unilateral moderate-severe PN
– Postnatal US at 2–4 wk
– VCUG at 2–4 wk if hydro present on postnatal US
– Consider diuretic nuclear renal scan (MAG-3) at 4 wk of hydro present on postnatal US
• Bilateral moderate-severe PN
– 1st postnatal US 1–3 days after birth
– VCUG 1–7 days after birth
– Males: Early VCUG to rule out PUVs
– Consider diuretic nuclear renal scan (MAG-3) at 4 wk
• Special situations: Bladder/urethral abnormalities, decreased amniotic fluid
– Early evaluation similar to severe bilateral PN
• Postnatal US within 48–72 hr after birth may underestimate degree of hydronephrosis
• Rare cases of pulmonary compromise from mass effect require emergent drainage
Diagnostic Procedures/Surgery
Fet al urinary electrolyte bladder aspiration in cases of oligohydramnios
Pathologic Findings
N/A
DIFFERENTIAL DIAGNOSIS
• Urinary conditions:
– Autosomal recessive polycystic kidney disease
– Duplication anomalies
– Ectopic ureter
– Megacystis-megaureter microcolon syndrome
– Multicystic dysplastic kidney
– PUVs
– Prune belly syndrome
– Transient hydronephrosis
– UPJ obstruction
– UVJ obstruction
– Vesicoureteral reflux
• Intestinal disorders:
– Cloacal exstrophy
– Duodenal atresia
– Imperforate anus
– Intestinal duplication
– Mesenteric cysts
– Ovarian cysts
– Persistent cloaca
• Tumors:
– Congenital mesoblastic nephroma
– Neuroblastoma
TREATMENT
GENERAL MEASURES
• Prenatal management: Assessment of hydronephrosis, oligohydramnios:
– Unilateral cases: Serial prenatal US if severe; deliver at term
– Bilateral cases
No oligohydramnios: Observation, deliver at term
Oligohydramnios: Termination, early delivery, prenatal treatment for pulmonary immaturity
• Postnatal management:
– Pulmonary support if respiratory compromise
– Antibiotic prophylaxis if moderate-severe unilateral or bilateral PN
– Bilateral hydronephrosis with dilated bladder: Place catheter to drain bladder
– All hydronephrosis: US, VCUG, MAG-3 renal scan as indicated (see above for SFU recommendations)
MEDICATION
First Line
• No specific antenatal medications exist
• Prophylactic antibiotics controversial.
– Recommended by SFU with moderate-severe PN, bladder/urethral abnormalities, dilated ureter, oligohydramnios(1)
– Amoxicillin (20 mg/kg/d—1 dose per day)
• Surfactant to assist lung function after birth with pulmonary hypoplasia
Second Line
N/A
SURGERY/OTHER PROCEDURES
• Fet al intervention (cases with oligohydramnios only):
– Controversial(3)
– Tapping of fet al bladder
– Percutaneous shunting: Vesicoamniotic drain
• Surgery is seldom necessary in the neonatal period with the exception of severe bilateral obstruction due to bladder outlet obstruction or severe UPJ or UVJ obstruction.
• Need for postnatal surgery based upon diagnosis and correlated with severity of PN
– Mild: <10%
– Severe: ∼50%
ADDITIONAL TREATMENT
Radiation Therapy
N/A
Additional Therapies
N/A
Complementary & Alternative Therapies
N/A
ONGOING CARE
PROGNOSIS
• Most neonates have an excellent prognosis. Prognosis depends on etiology of the dilated system and other associated anomalies.
• Severe bilateral hydronephrosis is associated with obstruction and oligohydramnios early in gestation predicts an adverse outcome.
• Fetuses with bilateral hydronephrosis, a distended bladder, and oligohydramnios are at highest risk of neonatal demise or pulmonary complications.
• Risk of UTI correlated with severity of PN
– Mild: ∼10%
– Moderate-severe: ∼30%
COMPLICATIONS
• Pulmonary hypoplasia with severe oligohydramnios
• Renal impairment
• UTIs
FOLLOW-UP
Patient Monitoring
• Based on initial evaluation, subsequent imaging may be necessary (1)
• Most centers employ serial renal US every 3–6 mo for the 1st yr of life
• If febrile UTI, consider VCUG and/or MAG-3 renal scan
Patient Resources
• http://urology.ucsf.edu/patient-care/children/Hydronephrosis
• http://urology.ucsf.edu/patient-care/children/urinary-tract-obstruction/ureteropelvic-junction-obstruction
• http://urology.ucsf.edu/patient-care/children/additional/megaureter
• http://urology.ucsf.edu/patient-care/children/urinary-tract-obstruction/posterior-urethral-valves
REFERENCES
1. Nguyen HT, Herndon CD, Cooper C, et al. The Society for Fet al Urology consensus statement on the evaluation and management of antenatal hydronephrosis. J Pediatr Urol. 2010;6:212–231.
2. Lee RS, Cendron M, Kinnamon DD, et al. Antenatal hydronephrosis as a predictor of postnatal outcome: A meta-analysis. Pediatrics. 2006;118:586–593.
3. Morris RK, Malin GL, Khan KS, et al. Systematic review of the effectiveness of antenatal intervention for the treatment of congenital lower urinary tract obstruction. BJOG. 2010;117:382–390.
ADDITIONAL READING
Davenport MT, Merguerian PA, Koyle M. Antenatally diagnosed hydronephrosis: Current postnatal management. Pediatr Surg Int. 2013;29(3):207–214.
See Also (Topic, Algorithm, Media)
• Hydronephrosis/Hydroureteronephrosis (Dilated Ureter/Renal Pelvis), Pediatric
• Hydronephrosis/Hydroureteronephrosis (Dilated Ureter/Renal Pelvis), Prenatal Image 
• Megaureter, Congenital
CODES
ICD9
• 753.6 Atresia and stenosis of urethra and bladder neck
• 753.20 Unspecified obstructive defect of renal pelvis and ureter
• 753.29 Other obstructive defects of renal pelvis and ureter
ICD10
• Q62.0 Congenital hydronephrosis
• Q64.31 Congenital bladder neck obstruction
• Q62.39 Other obstructive defects of renal pelvis and ureter
CLINICAL/SURGICAL PEARLS
• Majority of prenatal/fet al hydronephrosis (especially mild) is transient with no clinical significance.
• VCUG is not recommended for unilateral mild hydronephrosis.
• Prophylactic antibiotics have not been shown to be effective. Not recommended in mild cases.
• Emergent evaluation by urologist should occur with:
– Severe bilateral prenatal hydronephrosis
– Severe unilateral prenatal hydronephrosis in solitary kidney
– Prenatal hydronephrosis with dilated bladder consistent with posterior urethral valves
– Severe prenatal hydronephrosis with pulmonary compromise from mass effect (rare)