Francine H. Einstein, MD, Peter S. Bernstein, MD, MPH


January 13, 2003


At 20-22 weeks' gestational age, high-resolution ultrasonography very often reports dilation of the renal pelvis of the fetus. Please suggest the follow-up and outcomes of such findings.


Francine H. Einstein, MD, Peter S. Bernstein, MD, MPH

Fetal hydronephrosis is the most common anomaly found on ultrasound during the second-trimester anatomical survey.[1] High-definition ultrasound generally can detect even mild cases of fetal hydronephrosis and often permits the localization of the level of urinary tract obstruction. Prognosis and management are largely based on the level and degree of urinary tract obstruction. Maternal-fetal medicine consultation is warranted when fetal hydronephrosis is encountered.

The diagnostic criteria for fetal hydronephrosis are somewhat controversial. The Society for Fetal Urology (SFU) uses a grading system (grade 0-4) based on the degree of upper urinary tract dilation. Others have based the diagnosis on renal pelvis anteroposterior (AP) diameter, the ratio of AP pelvis diameter to AP renal diameter, the presence of caliectasis, and gestational age of the fetus. The most sensitive, but least specific, criteria for the diagnosis of fetal hydronephrosis would be the following: (1) caliceal dilation of grade 2 or greater using the SFU scoring system; (2) a renal pelvis diameter of > 4 mm before 33 weeks' gestation and > 7 mm after 33 weeks' gestation; or (3) a renal pelvis/kidney ratio of > 0.28. However, using these criteria, many normal kidneys would be categorized as hydronephrotic. Clinically significant disease is more likely if: (1) a grade 3 or 4 hydronephrosis is present; (2) the renal pelvis diameter is > 10 mm; or (3) the renal pelvis/kidney ratio is > 0.5. The frequency of surveillance and intervention will vary depending on the degree of fetal hydronephrosis.[2] Although isolated fetal hydronephrosis does not significantly increase the age-related risk of Down syndrome, the presence of other ultrasound markers is associated with an increased risk of aneuploidy.[3]

The differential diagnosis of fetal hydronephrosis includes physiologic hydronephrosis, ureteropelvic junction obstruction, ureterovesical pathology, and bladder outlet obstruction. Physiologic hydronephrosis is a variant of normal physiology and may be related to maternal hydration and normal distention of the fetal bladder. Ureteropelvic junction obstruction and ureterovesical pathology -- which includes complete ureteral duplication with ectopic ureterocele, congenital megaloureter, and ureterovesical junction stenosis -- are ureteral obstructions of varying degree and level along the ureter (from the ureteropelvic junction to the bladder insertion) and may be unilateral or bilateral. Prognosis is generally good in these conditions, even when surgical repair is needed. Bladder outlet obstruction may be caused by posterior urethral valves, urethral atresia, cloacal malformation, prune belly syndrome or megacystic-microcolon-intestinal hypoperistalis syndrome. Because these types of obstructions are distal to the bladder, the hydronephrosis is bilateral and may lead to significant renal dysfunction. Prognosis in these cases relates to the degree of renal insult. In cases where oligohydramnios is present, the prognosis is generally poor and related to pulmonary hypoplasia.

The initial management of the newborn with hydronephrosis is based on severity. The postnatal evaluation includes determination of the level of serum creatinine, a renal/bladder ultrasound, and a voiding cystourethrography. In cases of severe hydronephrosis, a radionuclide renography may be performed with or without a diuretic challenge to quantitate relative renal function. Early surgical intervention is undertaken for a palpable mass, severe bilateral hydronephrosis with elevated creatinine, or obstruction of a solitary kidney.


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