PRACTICE POINT

10 NATURE CLINICAL PRACTICE UROLOGY JANUARY 2007 VOL 4 NO 1

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Original article Coplen DE et al. (2006) The magnitude of fetal renal pelvic dilatation can identify obstructive postnatal hydronephrosis, and direct postnatal evaluation and management. J Urol 176: 724–727

SYNOPSISKEYWORDS hydronephrosis, obstruction, prenatal diagnosis, prenatal ultrasonography, renal pelvic dilatation

BACKGROUNDFetal renal pelvic dilatation (RPD) is detected in approximately 1% of all prenatal ultrasounds, making it one of the most common ultrasound-detected abnormality. The majority of patients with prenatally detected RPD have no significant clinical findings during infancy, but the condition is linked with postnatal problems such as renal obstruction in around 25% of patients. A reliable means of discriminating between benign tran-sient prenatal dilatation and dilatation linked with later renal obstruction is, therefore, required.

OBJECTIVETo determine whether fetal renal pelvic measure ments can predict the development of obstructive postnatal hydronephrosis and so direct prenatal counseling and postnatal management.

DESIGNThis study was a retrospective analysis of prospectively collected measurements of maximum anteroposterior prenatal RPD recorded at a single fetal–maternal medicine center between 1990 and 2003.

INTERVENTIONFetuses with RPD ≥4 mm at <33 weeks of gestation, or ≥7 mm at >33 weeks of gestation were included in the study. Infants with dupli-cation anomalies or multicystic dysplasia were excluded from the analysis. Infants were treated with amoxicillin prophylaxis (20 mg/kg/day)

Degree of fetal renal pelvic dilatation predicts postnatal obstruction

and underwent ultrasonographic evaluation at 3–4 weeks of age. Voiding cystourethrograms and renal scintigraphy were also performed on most infants.

OUTCOME MEASURESPostnatal renal obstruction (defined by the need for surgery because of reclining renal function or increasing hydronephrosis) was the main outcome variable. Patients who did not undergo surgery were followed up until the RPD resolved or stabilized, at which point they were considered to have nonobstructive dilatation.

RESULTSThe study included 257 neonates with prenatally- detected RPD seen at the center during the 13-year study period. The mean and median follow-up periods were 24 and 12 months, respectively. A total of 62 patients (24%) under-went surgery for obstruction (dismembered pyeloplasty in 55 and tapered ureteral implanta-tion in 7) and were, therefore, defined as having obstructive dilatation. The mean maximum prenatal RPD was approximately twice as high in patients with obstructive dilatation, compared with those with nonobstructive dilatation (22.3 mm vs 11.8 mm, respectively; P = 0.0001). Using receiver- operating- characteristic analy sis, an RPD threshold of 15 mm was found to correctly predict obstruction in at least 80% of fetuses, with a sensitivity of 73% and a specificity of 82%.

CONCLUSIONThe results of this study show that the magni-tude of fetal RPD is predictive of the develop-ment of postnatal obstructive dilatation, and that a fetal RPD of 15 mm is a significant threshold. These results could provide a useful guide for prenatal counseling and help to tailor postnatal evaluation and monitoring.

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PRACTICE POINT

JANUARY 2007 VOL 4 NO 1 NATURE CLINICAL PRACTICE UROLOGY 11

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AcknowledgmentsThe synopsis was written by Carol Lovegrove, Freelance Medical Writer.

Competing interestsThe author declared he has no competing interests.

CorrespondenceDepartment of UrologyHarvard University 355300 Longwood AvenueBostonMA 02115USAhiep.nguyen@childrens.harvard.edu

Received 15 August 2006Accepted 6 October 2006

www.nature.com/clinicalpracticedoi:10.1038/ncpuro0651

COMMENTARY

Hiep Nguyen

Hydronephrosis is one of the more common congenital anomalies detected on prenatal ultrasound, with an incidence of approximately 1–2%. With the development of improved ultrasound equipment, such as higher resolu-tion transducers, the detection rate of prenatal hydronephrosis is increasing. Consequently, more pregnant women are being referred for prenatal counseling, and even more newborns are being referred for postnatal evaluation. A diagnosis of prenatal hydronephrosis causes great concern for the expecting parents,1 with thoughts of renal failure and the possible need for dialysis. In actuality, the majority (80–85%) of children with prenatal hydronephrosis do not have any clinically significant renal pathology2 and do not require extensive postnatal radiologic evaluation. Some of these patients, however, do need further postnatal evaluation, in order to diagnose potential renal obstruction and other urinary-tract pathologies. The difficulty lies in determining which are the patients we need to be concerned about.

Anteroposterior renal pelvic diameter (APRPD) seems to be a reliable parameter for differentiating between clinically signifi-cant obstruction of the upper urinary tract and benign transient dilatation. In this study, Coplen et al. demonstrate that fetuses with an APRPD greater than 15 mm (detected on ultra-sound) had a fourfold increased risk of having a ureteropelvic-junction obstruction requiring postnatal surgical correction. The indications for surgical correction in the study were decreased renal function seen on renal scintigraphy and increasing hydronephrosis noted on serial ultra-sound. The changes most commonly occurred during the first 12 months of life.

The findings from this study greatly increase our ability to counsel parents, and should guide clinicians in the postnatal work-up. We are now able to advise parents that a newborn with prenatally diagnosed hydronephrosis has

a higher likelihood of requiring surgery to correct renal obstruction if the APRPD is greater than 15 mm, and that the need for surgery is likely to be higher during the first year of life. Additionally, these findings tell physicians that fetuses in whom the APRPD is greater than 15 mm will require more intensive postnatal work-up, including renal scintigraphy. The ability to differentiate between those who will need earlier and more frequent follow-up and those who do not need any intervention will alleviate much anxiety for both the parents and the physicians.

While APRPD is a reliable parameter for predicting obstructive pathology, it should be noted that additional findings on prenatal ultrasound can also help to predict possible pathology, including the sex of the fetus, amniotic fluid levels, dilatation of the calyces or ureters, and bladder abnormalities.3 Unfortunately, no studies have evaluated all of these parameters simultaneously to deter-mine the likelihood of urinary-tract pathology. In addition, there remains a debate as to how accurate postnatal imaging tests, such as diuresis renography, are in diagnosing urinary-tract obstruction that will lead to renal functional impairment (rather than just simple dilatation of the urinary tract without any compromise to renal function). Prospective studies evaluating the natural history of prenatal hydronephrosis and its correlation with prenatal ultrasound parameters are needed to make complete and accurate prenatal counseling possible.

References1 Harding LJ et al. (1999) Antenatal minimal

hydronephrosis: is its follow-up an unnecessary cause of concern? Prenat Diagn 19: 701–705

2 Lee RS et al. (2006) Antenatal hydronephrosis as a predictor of postnatal outcome: a meta-analysis. Pediatrics 118: 586–593

3 Oliveira EA et al. (1999) Prognostic factors in fetal hydronephrosis: a multivariate analysis. Pediatr Nephrol 13: 859–864

H Nguyen is an Assistant Professor in Surgery (Urology) at Harvard Medical School, Boston, MA, USA.

PRACTICE POINTChildren with prenatal hydronephrosis and an anteroposterior renal pelvic diameter of >15 mm require postnatal evaluation and are likely to need surgical correction for renal obstruction during the first year of life

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