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Antenatal Hydronephrosis

The anomalous development of the urinary tract can now be recognized in utero, thereby prompting and permitting the evaluation of congenital uropathies prior to the onset of complications or symptomatology. The widespread use of screening maternal and fetal ultrasonography (US) has understandably revolutionized the specialty of pediatric urology.

In the recent past most children with congenital uropathies presented with an abdominal mass, sepsis or urinary tract infection, hematuria, voiding dysfunction, urinary incontinence, failure to thrive, ascites or pain. Some patients remained asymptomatic until adulthood, whereas others were discovered serendipitously in the course of some unrelated radiologic investigation.

Congenital uropathies are now detected in utero with regularity. Although antenatal US may not precisely diagnose the pathology, the impetus for further evaluation is present at birth. Postnatally, with the aid of various imaging modalities, the nature of the pathology can be formulated.

Through the diction of urinary tract dilation or cystic changes maternal/fetal US identifies those neonates who need early evaluation and who potentially would benefit from early treatment. The benefits implicit in early diagnosis are the ability to intervene prior to the development of complications and the preservation of renal function. A successful clinical outcome depends upon our capacity to define obstruction and then prognosticate regarding the potential for recovery. Our technologic ability to recognize upper tract dilation has unfortunately outpaced our ability to define obstruction. Without such a definition, the decision to observe or operate often remains quite subjective and controversial. Therein lies the urologist’s predicament, i.e. who can be managed non-operatively, who requires reconstructive surgery, and when should the necessary surgery be performed.

Newborns with histories of antenatal Hydronephrosis require early postnatal evaluation. Currently there is no imaging modality or functional investigation that unequivocally distinguishes obstructive and non-obstructive dilation. Despite the fact that some of these infants and young children do well with non-operative management, truly obstructive lesions ultimately jeopardize some or all of the functional renal mass.

Ultrasonography, voiding cysto-urethrography (VCUG), intravenous pyelography (IVP), and diuretic renography (DR), are used in various combinations to evaluate the nature of the dilated upper urinary tract. Recently duplex Doppler US has been added to the diagnostic armamentarium. Diuretic renography, more than any other imaging technique, has been widely promoted as the test of choice because of its ability to “quantify” the washout of radioisotope from the upper tracts. Despite an extensive literature espousing the advantages of one imaging modality over another, insufficient data exists regarding the evaluation of upper urinary tract dilatation in infants and young children, such that a gold standard remains elusive.

A thorough background in the embryology and anatomy of the urinary tract, and a clear understanding of transitional neph-rology, are necessary to formulate a strategy for diagnostic imaging and a comprehensive plan of management.

Antenatal Diagnoses

Congenital uropathies are discovered in approximately 0.5% of screening maternal-fetal US examinations. Serial studies are indicated after discovering antenatal Hydronephrosis in order to assess progression or resolution. Fur-thermore, extra urinary anomalies must be sought as the incidence of compounding anomalies approaches 55%. Such a practice helps to establish perspective and facilitates counseling of the expectant parents.

The most common urologic diagnoses include: Hydronephrosis, posterior urethral valves, duplex kidneys, multicystic dysplasia, prune belly syndrome, autosomal recessive polycystic kidney disease, Potter’s syndrome and renal agenesis. Classic and cloacal exstrophies, cloacal anomalies and imperforate anus, neuroblastoma and mesoblastic nephroma can also be detected.

Hydronephrosis is overwhelmingly the most common finding and may be physiologic and non-obstructive or it may be secondary to obstruction at the ureteropelvic or ureterovesical junctions, vesicoureteral reflux, ureteroceles, duplications or bladder outlet obstruction. It is our job to distinguish between obstructive and non-obstructive processes. The widespread use of maternal/fetal US has created an epidemic of asymptomatic infants in whom this clinical question must be answered.

Postnatal diagnostics & Management

Truly obstructive lesions produce renal ischemia and loss of function. Infection makes matters worse and increases the risk for permanent renal injury. Surgical correction of suspected obstruction is highly successful in infants and children of all ages. The natural history of non-operated Hydronephrosis is poorly defined however, and the validity of the diagnostic tests used for assessing these dilated upper urinary tracts remains unproven. Understandably, the management of these children is controversial.

The postnatal US is best delayed until the 3rd day of life. Earlier studies have a good chance of being falsely normal owing to a low glomerular filtration rate and relative dehydration. If Hydronephrosis is confirmed, we recommend placing the infant on amoxicillin 10mg/kg/day.

If antenatally there is suspicion for posterior urethral valves (PUV), significant (grade 3 or 4) bilateral Hydronephrosis or unilateral hydro-nephrosis in a solitary functioning kidney, then the postnatal US should be performed without delay and followed by the VCUG. In these cases serum chemistries should also be checked closely, and any additional workup (DR in the case of hydronephrosis) or intervention (valve resection or vesicostomy in the case of PUV) should be expedited.

A VCUG is performed within a month of age (44 weeks post conception) even if the postnatal US was normal because 25% of the infants with normal postnatal studies will have reflux, while more than 40% of those with persistent hydronephrosis will have reflux. If reflux is diagnosed the children are generally switched over to TMP-SMX after 1 month of age and are maintained on antibiotic suppression until the reflux has resolved.

In the absence of reflux, DR is then performed. The DR should be performed in a pediatric nuclear medicine facility that adheres to the “well-tempered renogram” protocol developed by the Society for Fetal Urology and the Pediatric Nuclear Medicine Club.

Criteria for obstruction are in a state of evolution. Obstruction, according to DR, is defined by the following criteria: (1) prolonged, flat or rising time-activity curves, and (2) T1/2 – 20 minutes. A T1/2 < 10 minutes by definition connotes prompt drainage, while a T1/2 between 10 and 20 minutes is equivocal. Surgery for the correction of obstruction is also indicated in the presence of: (1) differential renal function less than 40%, (2) recurrent UTI, (3) increasing hydronephrosis, and (4) compensatory renal growth of the contralateral normal kidney.

If ureteral obstruction is found, (whether it lies at the UPJ, UVJ or mid ureter), surgery is required. If non-obstructive dilatation diagnosed, or if our imaging studies are equivocal, then the US should be repeated approximately every 3 months for the first year, and DR is repeated if there is a change for the worse or the clinical situation changes.

Multicystic dysplastic kidneys are followed by serial US studies. Dysplastic kidneys require removal only if their size presents problems with pulmonary or gastrointestinal function, they increase in size rather than regress over time, or if they are associated with infection. Associations between multicystic and hypertension and malignancy remain anecdotal at this time.

Duplex kidneys with or without ureteroceles are managed according to the clinical situation and the effect, if any, on all existing functioning moieties. If a neurogenic bladder or prune belly syndrome is discovered then bladder function must be assessed and efficient emptying must be assured.


Surgery for the correction of urinary tract obstruction is safe and definitive, and should be performed when obstruction is defined. Unfortunately, there is no gold standard for the evaluation of neonates and young infants. Newer and more refined tests, which assess renal blood flow and glomerular filtration, are necessary. Until such time these improved tests are available, children with antenatally detected hydronephrosis should be thoughtfully, carefully and thoroughly evaluated. Close surveillance can be practiced and continued until the hydronephrosis has resolved spontaneously or until obstruction has been proven.

Updated July 2002

The information above, although based on a thorough knowledge and careful review of current medical literature, is the opinion of the doctors at Urology for Children, LLC, and is presented to inform you about surgical conditions. It is not meant to contradict any information you may receive from your personal physician and should not be used to make decisions about surgical treatment. If you have any questions about the information above or your child’s care, please contact our doctors at any time by calling (856) 751-7880.