Antenatal hydronephrosis and postnatal evaluation

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Target exams

Red flags

• Antenatal bilateral severe hydronephrosis with oligohydramnios signalling obstructive uropathy and impending renal and respiratory failure
• A male fetus or neonate with a dilated thick-walled bladder and bilateral hydronephrosis indicating posterior urethral valves until proven otherwise
• A solitary kidney with antenatal hydronephrosis because there is no renal reserve and obstruction must be excluded immediately after birth
• Worsening anteroposterior renal pelvic diameter across serial antenatal scans suggesting progressive obstruction rather than transient dilatation
• Echogenic or cystic renal parenchyma accompanying the dilatation because this indicates dysplasia and a poor long-term renal prognosis
• A palpable abdominal mass or a poor urinary stream in the newborn period in a baby with antenatal hydronephrosis

Life stages

Care settings

Clinical exam formats

Board mappings

• Defines antenatal hydronephrosis as renal pelvic dilatation detected on antenatal ultrasound and distinguishes transient physiologic dilatation from pathological obstruction and reflux
• States that the first postnatal ultrasound should be deferred to at least 48 hours and ideally days 5 to 7 to avoid the false negative of neonatal dehydration
• Initiates prophylactic antibiotics for high-risk findings and refers for specialist urological and nephrology evaluation
• Applies the Society for Fetal Urology grading system and the Urinary Tract Dilation classification system with the anteroposterior renal pelvic diameter thresholds at the 28-week gestational cutoff
• Constructs the postnatal investigation pathway of ultrasound, MCUG, DMSA, and MAG3 and states the indication for each
• Counsels on the long-term chronic kidney disease risk from the underlying congenital anomaly and the rationale for life-long nephrology surveillance
• SFU grading and UTD classification thresholds and the difference between the antenatal and postnatal systems
• Postnatal ultrasound timing and the false negative of early imaging plus the exceptions that demand immediate imaging
• Risk stratification into low-risk and increased-risk categories and the investigation and antibiotic pathway for each
• Assesses a newborn with an antenatally detected renal finding and constructs a structured postnatal evaluation plan
• Communicates the diagnosis, prognosis, and surveillance plan for a family whose infant has antenatal hydronephrosis
• Recognises the infant with posterior urethral valves and coordinates urgent decompression and specialist referral
• Level 1: Recognition of antenatal hydronephrosis and the difference between physiologic and pathological dilatation
• Level 2: Initiation of correctly timed postnatal ultrasound and prophylactic antibiotics for high-risk findings
• Level 3: Coordination of multidisciplinary urology and nephrology care and long-term chronic kidney disease surveillance
• The SFU grading system from grade 0 to grade 4 and the UTD classification with the anteroposterior diameter thresholds
• The 28-week gestational age cutoff and the antenatal and postnatal risk categories
• The investigation pathway of ultrasound, MCUG, DMSA, and MAG3 and the timing of the first postnatal scan
• Assessment of a newborn with an antenatal renal finding and construction of the postnatal plan
• Interpretation of the renal ultrasound, MCUG, DMSA scan, and MAG3 renogram in a child with antenatal hydronephrosis
• Structured explanation of the management, the grading, and the long-term surveillance
• SFU grading and UTD classification and the anteroposterior diameter thresholds at each gestational age
• Postnatal ultrasound timing at days 5 to 7 and the antibiotic prophylaxis pathway for high-risk findings
• Long-term complications including chronic kidney disease, hypertension, and recurrent urinary tract infection
• Recognition of antenatal hydronephrosis as the gateway finding for congenital anomalies of the kidney and urinary tract
• Correct timing of the first postnatal ultrasound and initiation of prophylactic antibiotics for high-risk findings
• Family communication around the grading, the prognosis, and the surveillance plan
• Canadian approach to antenatal hydronephrosis with standardised antenatal and postnatal imaging protocols
• Risk stratification using the UTD classification and the threshold for specialist referral
• Transition of care from paediatric to adult nephrology for young adults with a confirmed congenital anomaly