Evaluation of infants with prenatally diagnosed hydronephrosis: Subsequent evaluation and management based on postnatal ultrasound findings

This figure summarizes our suggested approach to the evaluation and initial management of infants with prenatally diagnosed hydronephrosis. The most common causes of hydronephrosis in this setting are benign transitional hydronephrosis and congenital UPJ obstruction. Postnatal evaluation is generally warranted if the prenatal ultrasound performed in the 3^rd trimester had a minimum RPD of 10 mm. RPDs below this level are unlikely to be associated with CAKUT. For neonates with RPD ≥10 mm on prenatal ultrasound, the timing of the postnatal ultrasound and need for prophylactic antibiotics depend on the severity of the findings. If the postnatal kidney ultrasound is performed in the first few days after birth and is normal or shows only mild hydronephrosis, a repeat ultrasound should be performed at several weeks of age. This is because clinically significant hydronephrosis may not be seen on early postnatal imaging, due to relative dehydration in the early newborn period. For additional details, refer to UpToDate topics on hydronephrosis and CAKUTs.

CAKUT: congenital anomalies of the kidney and urinary tract; MRI: magnetic resonance imaging; PUV: posterior urethral valve; RPD: renal pelvic diameter; UPJ: ureteral pelvic junction; UTI: urinary tract infection; VCUG: voiding cystourethrogram; VUR: vesicoureteral reflux.

* The postnatal ultrasound is considered normal if there is no renal pelvis dilation nor evidence of any other genitourinary abnormality (ie, no calyceal or ureteric dilation, no signs of renal dysplasia or anomalies).

¶ Congenital UPJ obstruction is the most common pathologic cause of prenatally diagnosed hydronephrosis. Findings on kidney ultrasound that suggest UPJ obstruction include unilateral hydronephrosis with nondilated ureter, normal bladder, and normal contralateral kidney. The diagnosis is confirmed with diuretic renal scan, which is typically performed after 6 weeks of age. Less frequently, MRI may be used to confirm the diagnosis. Expert opinion differs as to whether VCUG is necessary in the evaluation of infants with unilateral hydronephrosis with nondilated ureter and normal bladder. Our practice is to not routinely perform VCUG in this setting. Other experts routinely perform VCUG to definitively exclude VUR since a small minority of patients with UPJ obstruction may also have VUR. Another relatively common cause of prenatally diagnosed hydronephrosis is primary megaureter, which is due to a functional or anatomical abnormality at the ureterovesical junction. For additional details, refer to separate UpToDate content on congenital UPJ obstruction and primary megaureter.

Δ Follow-up ultrasound may not be necessary if the initial postnatal ultrasound was performed after 3 to 4 weeks of age and showed only mild hydronephrosis (RPD <10 mm). However, in most cases, it is reasonable to repeat the ultrasound at 4 to 6 months of age to definitively exclude a urologic abnormality. If the ultrasound findings are improved or stable, this confirms the diagnosis of transitional hydronephrosis and the patient does not require further urologic follow-up.

◊ PUV is treated surgically. Management of VUR may include observation, medical management including antibiotic prophylaxis, or surgical correction for more severe grades of VUR. Refer to separate UpToDate content on VUR and PUV for additional details.

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Evaluation of infants with prenatally diagnosed hydronephrosis: Subsequent evaluation and management based on postnatal ultrasound findings