Management of neonatal hydronephrosis

Abstract

Management of neonatal hydronephrosis is a clinical challenge. The natural history of hydronephrosis has shown that most resolve spontaneously; however, there are a significant number that do not. Although hydronephrosis does not always mean obstruction, it becomes the clinician's role to determine when obstruction will eventually lead to renal damage. Work-up of hydronephrosis diagnosed prenatally starts with a postnatal ultrasound. Using the Society of Fetal Urology (SFU) grading of hydronephrosis based on ultrasonography, a management and treatment algorithm can be constructed. Other studies include a voiding cystourethrogram to evaluate for vesicoureteral reflux or in severe cases of bilateral hydronephrosis to evaluate for posterior urethral valves. Diuretic renography is useful in many cases to evaluate the degree of obstruction and determine differential renal function. The goal is to select the patients who would benefit from early surgical intervention. To achieve that goal, aggressive observation is often required.

Introduction

The introduction of fetal ultrasonography (US) has allowed for the detection of many intrauterine anomalies. Indeed, most anomalies are detected during routine fetal US done at 18–20 weeks gestation. Urinary tract anomalies are particularly readily identified. Of these, hydronephrosis is the most common, comprising 50% of congenital malformations [1]. Fetal hydronephrosis is found in 0.59% [2] to 1.4% of fetuses [3]. However, hydronephrosis does not necessarily translate into obstruction. Moreover, many cases of neonatal hydronephrosis improve or resolve spontaneously without surgical intervention [2]. The dilemma becomes which renal units would best be operated on and which can be observed. The purpose of this article is to review the current literature on the management of neonatal hydronephrosis, establish clinical guidelines and discuss future research directions to help understand better the natural history of neonatal hydronephrosis.

To standardize and categorize neonatal hydronephrosis better, the Society of Fetal Urology (SFU) developed a grading system based on the long-axis sonographic appearance of the renal parenchyma and pelvicalyceal system (Table 1). In Fig. 1, examples of SFU grades 0 to IV are depicted. Only grades III and IV are thought to be clinically significant postnatally. Another description of the degree of hydronephrosis is the measurement of the maximum antero-posterior diameter of the pelvis, or the renal pelvic diameter (RPD). Controversy exists pertaining to the threshold RPD that is considered abnormal in the fetus [2] especially noting that this may change with gestational age. Most clinicians consider an RPD > 6 mm late in gestation to be indicative of hydronephrosis worthy of postnatal follow-up [4].

The most common causes of neonatal hydronephrosis are transient and physiologic hydronephrosis accounting for approximately 60% of cases [2]. The natural history of these cases appears to be benign. In one series [5], 45 infants with hydronephrosis were followed for 30 months and mild hydronephrosis was seen in 30. All did well. Of the 15 infants with severe hydronephrosis, most also did well, with some showing improvement in function measured by diuretic renography. In one somewhat atypical and unique series, Koff and Campbell followed 104 patients for 5 years and only seven (7%) required pyeloplasty, as determined by progression of hydronephrosis and/or greater than 10% reduction in glomerular filtration rate on renography [6]. Although these patients did better than most others in the literature, this demonstrates that many cases, even severe ones may do well.

Another common cause of neonatal hydronephrosis is significant ureteropelvic junction obstruction (UPJO) which accounts for approximately 10% of prenatal hydronephrosis. The male-to-female ratio in infancy is 3:1 and the hydronephrosis is bilateral in up to 20–25% of cases, though most commonly the contralateral hydronephrosis is not significant [2]. The etiology in neonates is usually an intrinsic stenosis followed by a kink. It is usually suspected prenatally when there is hydronephrosis with a very large renal pelvis (> 3 cm in A–P diameter), no ureteral dilation and normal bladder and normal amniotic fluid volume.

Vesicoureteral reflux is found in up to 33% of cases of prenatal hydronephrosis [7]. Interestingly, males predominate in these cases and these infants have a high spontaneous resolution rate. In some series, 65% resolve within 2 years including an appreciable number of severe grades IV and V reflux [2].

Ureterovesical junction obstruction constitutes about 4% of the causes of neonatal hydronephrosis and is suggested when the US shows a dilated ureter (> 7 mm) as well as hydronephrosis and a voiding cystourethrogram (VCUG) shows no reflux. Posterior urethral valves (PUV), multicystic dysplastic kidney and ureteroceles constitute between 2% and 4% of the cases [2]. Table 2 lists the principal causes of neonatal hydronephrosis.