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Postnatal evaluation of antenatally diagnosed fetal hydronephrosis
Laurence Baskin, MD
UpToDate performs a continuous review of over 350 journals and other resources. Updates are added
as important new information is published. The literature review for version 14.1 is current through
December 2005; this topic was last changed on February 24, 2003. The next version of UpToDate
(14.2) will be released in June 2006.
INTRODUCTION — Fetal hydronephrosis is often identified on antenatal ultrasound examination.
Although it is transient in most cases, causes include urinary tract obstruction and vesicoureteral
reflux. These conditions may prevent normal renal development or cause renal injury. Newborns with
antenatally diagnosed hydronephrosis require evaluation soon after birth to determine the etiology
and to minimize adverse outcomes.
The postnatal evaluation of antenatally diagnosed hydronephrosis is reviewed here. Specific urologic
conditions that may present as antenatal hydronephrosis are discussed separately. (See "Ureteropelvic
junction obstruction; congenital megaureter; ureterocoele; and ectopic ureter").
ANTENATAL HYDRONEPHROSIS — Hydronephrosis is an abnormality commonly identified on antenatal
ultrasound examination. It can be detected reliably after the 18th week of gestation. (See "Prenatal
diagnosis of fetal pyelectasia; vesicoureteral reflux; and hydronephrosis").
Definition — The most generally accepted measurement used to define antenatal hydronephrosis is
the maximum anteroposterior diameter of the renal pelvis (APPD), or renal pelvic diameter (RPD) [1].
The threshold above which the renal pelvic diameter is considered abnormal is controversial. This
measurement depends in part upon the gestational age of the fetus. A value >5 mm during the third
trimester of pregnancy has been commonly used to indicate hydronephrosis [1].
Epidemiology — The incidence of antenatal hydronephrosis depends upon the definition of the
disorder. In a prospective study, RPD greater than 5 mm was detected in 100 of 18,766 women (0.59
percent) who had detailed antenatal ultrasonography [2]. In another prospective study of
ultrasonographic screening in 6292 women, hydronephrosis (defined as RPD >10 mm) occurred in 92
(0.65 percent) [3].
Hydronephrosis occurs approximately twice as often in males than in females. It is bilateral in 20 to
40 percent of cases [4].
Etiology — Most cases of antenatal hydronephrosis are found to be transient (48 percent) or
physiologic (ie, less than 5 mm [15 percent]) on postnatal evaluation [1]. However, obstruction of the
urinary tract is an important cause that must be evaluated. The obstruction may be ongoing (eg,
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posterior urethral valves), with the need for urgent surgical intervention to prevent further damage
[5]. Alternatively, it may be due to a prior antenatal event that has resolved, in which case no further
damage will occur and surgery is unnecessary [5]. Dilatation of the urinary tract also can occur
without obstruction, such as that caused by vesicoureteral reflux.
One review found the following causes of antenatal hydronephrosis and their approximate frequency
[1]:
z
z
z
z
z
z
z
z
Transient — 48 percent
Physiologic — 15 percent
Ureteropelvic junction (UPJ) obstruction — 11 percent
Vesicoureteral reflux (VUR) — 9 percent
Megaureter (obstructed or unobstructed) — 4 percent
Multicystic dysplastic kidney — 2 percent
Ureterocoele — 2 percent
Posterior urethral valves — 1 percent
Less common causes include ectopic ureter, prune belly, urachal cyst, and urethral atresia.
Severity — The severity of hydronephrosis is graded according to the extent of increase in the RPD. In
the third trimester, we define an RPD of 5 to 8, 8 to 12, and >12 mm as mild, moderate, and severe
hydronephrosis, respectively.
A classification system (grades I through IV) for prenatal hydronephrosis has been developed by the
Society of Fetal Urology (SFU) (show figure 1) [6]. SFU grade 0 corresponds to an intact central renal
complex (ie, renal pelvis). SFU grade I corresponds to mild splitting. Grade II indicates pelviectasis
but no calyectasis; the complex is defined within the renal border. Grade III has both a markedly split
pelvis that is dilated outside the renal border and uniformly dilated calyces, but normal renal
parenchyma. Grade IV has the characteristics of Grade III plus thinning of the renal parenchyma. This
system is used to guide evaluation and to predict outcomes for affected patients.
In general, the likelihood of having a significant renal anomaly correlates with the severity of
hydronephrosis. In addition, the underlying diagnosis often determines the extent of dilatation. A
frequent cause of marked hydronephrosis is UPJ obstruction, whereas milder dilatation is often caused
by VUR.
PHYSICAL EXAMINATION — The infant with antenatal hydronephrosis should be examined to detect
the presence of an abdominal mass that could represent an enlarged kidney due to UPJ obstruction or
multicystic dysplastic kidney. A palpable bladder in a male infant, especially after voiding, may
suggest posterior urethral valves. A male infant with prune belly syndrome will have deficient
abdominal wall musculature and undescended testes. The presence of associated anomalies should be
noted. (See "Examination of the newborn").
RADIOLOGIC STUDIES — Postnatal radiologic evaluation of a newborn with antenatal hydronephrosis
begins with an ultrasound examination. Subsequent investigations and their timing depend upon the
severity of the hydronephrosis.
Ultrasound examination — Affected infants should have an ultrasound examination of the kidneys and
bladder in the postnatal period. The timing of the study depends upon the severity of the antenatal
hydronephrosis. In general, examination should be avoided in the first two days after birth because
hydronephrosis may not be detected because of physiologic volume depletion and relative oliguria.
However, infants with bilateral hydronephrosis who are suspected of having posterior urethral valves
or a ureterocoele and those with a single kidney that is hydronephrotic require urgent evaluation on
the first postnatal day.
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Voiding cystourethrogram — A voiding cystourethrogram (VCUG) is performed to detect VUR. In boys,
VCUG also is used to evaluate the posterior urethra.
For this procedure, a urinary catheter is inserted into the bladder and contrast material is instilled.
Fluoroscopic monitoring is performed while the bladder is filling and during voiding. Infants usually
tolerate this procedure well. Although the duration of fluoroscopy is minimized, the gonads, especially
the ovaries, are exposed to radiation [1].
Diuretic renography — Diuretic renography is a functional study used to diagnose urinary tract
obstruction in infants with persistent hydronephrosis, especially if the VCUG has shown no VUR [7].
The test can assess total and individual renal function and the drainage time from the renal pelvis.
The test requires insertion of a bladder catheter to relieve any pressure that can be transmitted to the
ureters and kidneys. Intravenous access is needed for hydration and the administration of the
radioisotope and diuretic.
In the first phase of the study, a small dose of radioisotope is injected intravenously and renal
parenchymal uptake is analyzed during the first two to three minutes. The preferred radioisotope in
newborns and infants is technetium-99m-mercaptoacetyltriglycine (Tc99mMAG3), which has cortical
uptake as well as tubular excretion [8]. At peak renal uptake, intravenous furosemide is administered
and the excretion of isotope is measured.
Interpretation — In the initial two to three minutes, the radioisotope is distributed in the renal
parenchyma. The relative contribution of each kidney to overall renal function is assessed
quantitatively. It is known as the split renal function and is useful as a baseline study. Subsequent
studies can be compared to assess whether kidney function remains stable or has deteriorated,
suggesting true obstruction [9].
The second phase of the study is the "washout curve," the half-life (t1/2) for the radioisotope to drain.
This phase indicates the extent of obstruction, if present. In the normal kidney, the administration of
furosemide results in a prompt washout. In a dilated system, if washout occurs rapidly after diuretic
administration, the system is not obstructed. With conventional interpretation, if washout is delayed
beyond 20 minutes, the pattern is considered obstructed.
However, delayed washout curves that occur with a long t1/2 must be interpreted with caution
because a substantial proportion of studies interpreted as obstructed do not predict renal damage
[5,10]. As an example, in a series of 39 infants with antenatal unilateral hydronephrosis followed
without surgery, diuretic renography indicated obstruction in 24 patients whose renal function never
decreased and thus could not have been obstructed [10]. If washout is between 15 and 20 minutes,
the study is indeterminant.
Intravenous urogram — The combination of renal ultrasound and diuretic renography has replaced the
intravenous urogram (IVU) as a technique to evaluate renal anatomy and function in infants. This
technique requires the use of ionizing radiation and rarely reveals any additional useful information in
asymptomatic patients.
EVALUATION — An algorithm is used in order to make an accurate diagnosis of significant uropathy
while avoiding unnecessary tests in patients with physiologic or clinically insignificant hydronephrosis
[11]. This approach limits radiographic studies to those that are necessary and minimizes parental
distress [12,13].
Bilateral hydronephrosis — Infants with bilateral moderate to severe hydronephrosis, bladder
distension, or a dilated ureter in whom posterior urethral valves or a ureterocoele is suspected should
be evaluated as soon as possible after birth.
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Moderate to severe hydronephrosis — Newborns with moderate or severe antenatal hydronephrosis
are given antibiotic prophylaxis (amoxicillin, 12 to 25 mg/kg PO daily) until reflux is excluded. A
postnatal ultrasound examination should be performed after the infant reaches 48 hours of age.
Infants with persistent hydronephrosis should have a VCUG to detect VUR. VUR accounts for
approximately 9 percent of cases of antenatal hydronephrosis [1], but it is a more common cause (20
to 30 percent) in children with moderate to severe disease.
If the VCUG is negative (no reflux), infants with persistent moderate to severe hydronephrosis should
have a functional renal scan with Tc99mMAG3 to detect possible obstruction. In infants with a
negative VCUG and mild or no hydronephrosis, we repeat the ultrasound when they reach three
months of age and discontinue antibiotic prophylaxis if the hydronephrosis has not progressed.
Infants who have VUR demonstrated on VCUG should remain on antibiotic prophylaxis until the reflux
resolves. Renal scarring should be evaluated in infants with severe reflux (Grade III to V) with a
technetium 99m-dimercaptosuccinic acid (DMSA) scan.
Mild hydronephrosis — Infants with mild hydronephrosis do not need antibiotic prophylaxis because
the risk of reflux is relatively low. They should have an ultrasound examination after they reach seven
days of age. If the hydronephrosis remains mild or is not evident, ultrasonography should be repeated
at approximately three months of age.
Management of infants with moderate to severe hydronephrosis (SFU grade III or greater) on the
initial postnatal scan is similar to that for moderate to severe antenatal hydronephrosis. It includes a
VCUG to detect reflux, and antibiotic prophylaxis until reflux is excluded.
Use of UpToDate is subject to the Subscription and License Agreement.
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REFERENCES
Woodward, M, Frank, D. Postnatal management of antenatal hydronephrosis. BJU Int 2002;
89:149.
Dudley, JA, Haworth, JM, McGraw, ME, Frank, JD. Clinical relevance and implications of antenatal
hydronephrosis. Arch Dis Child Fetal Neonatal Ed 1997; 76:F31.
Livera, LN, Brookfield, DS, Egginton, JA et al. Antenatal ultrasonography to detect fetal renal
abnormalities: a prospective screening programme. BMJ 1989; 298:1421.
Gonzalez, R, Schimke, CM. Ureteropelvic junction obstruction in infants and children. Pediatr Clin
North Am 2001; 48:1505.
Koff, SA. Postnatal management of antenatal hydronephrosis using an observational approach.
Urology 2000; 55:609.
Fernbach, SK, Maizels, M, Conway, JJ. Ultrasound grading of hydronephrosis: introduction to the
system used by the Society for Fetal Urology. Pediatr Radiol 1993; 23:478.
Chung, S, Majd, M, Rushton, HG, Belman, AB. Diuretic renography in the evaluation of neonatal
hydronephrosis: is it reliable?. J Urol 1993; 150:765.
Taylor, A Jr, Clark, S, Ball, T. Comparison of Tc-99m MAG3 and Tc-99m DTPA scintigraphy in
neonates. Clin Nucl Med 1994; 19:575.
Gordon, I. Diuretic renography in infants with prenatal unilateral hydronephrosis: an explanation
for the controversy about poor drainage. BJU Int 2001; 87:551.
Gordon, I, Dhillon, HK, Gatanash, H, Peters, AM. Antenatal diagnosis of pelvic hydronephrosis:
assessment of renal function and drainage as a guide to management. J Nucl Med 1991; 32:1649.
Josephson, S. Antenatally detected pelvi-ureteric junction obstruction: concerns about conservative
management. BJU Int 2000; 85:973.
Ransley, PG. The postnatal management of hydronephrosis diagnosed by prenatal ultrasound. J
Urol 1990; 144:584.
Josephson, S, Dhillon, HK, Ransley, PG. Post-natal management of antenatally detected, bilateral
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hydronephrosis. Urol Int 1993; 51:79.
GRAPHICS
SFU grading fetal hydronephr
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