A 35-year-old pregnant woman underwent a 20-week structural ultrasound, and the fetus was found to have a left anterior-posterior renal pelvic diameter (APRPD) of 8 mm (urinary tract dilation [UTD] A2-3 [A = antenatal]) and a normal-appearing right kidney. The ureters of the fetus were not dilated and the bladder appeared normal. A slow but progressive increase in the left APRPD was observed during the third trimester of pregnancy. At 38 weeks, the left APRPD was 2.2 cm with peripheral caly-ceal dilation (UTD A2-3). The fetus was female. The amniotic fluid volume was normal. Vaginal delivery at 39 weeks was uneventful, and the infant’s Apgar score was 91/95.
The first postnatal sonogram at 1 week of age (Figure 1A) shows the left kidney ultrasound with UTD P3 (P = postnatal). A voiding cystourethrogram (VCUG) showed no reflux. A renogram at 6 weeks of age showed that the right kidney contributed 60% and the left contributed 40% to total renal function. Following administration of furosemide, there was delayed drainage on the left side. A second renal sonogram showed no improvement in the hydronephrosis (Figure 1B). Surgery was recommended, but the patient’s parents wanted to wait until after a family function. A renal sonogram at 3 months showed a slight worsening of the left hydronephrosis (Figure 1C). A dismembered left pyeloplasty was performed. No crossing vessel was noted. At postoperative month 3, renal ultrasound showed significant improvement in the hydronephrosis and interval growth of the kidneys (Figure 1D).
A 31-year-old pregnant woman had a normal 20-week structural ultrasound. At 32 weeks, the ultrasound showed a right APRPD of 1.5 cm with peripheral calyceal dilation (UTD A2-3). The left kidney of the fetus appeared entirely normal and the ureters were not dilated. The bladder of the fetus appeared normal. At 37 weeks, the APRPD was 2.0 cm (UTD A2-3). The fetus was male. Amniotic fluid volume was normal. Vaginal delivery at 40 weeks was uneventful, and the infant’s Apgar score was 91/95.
The first postnatal sonogram at 1 week of age (Figure 2A) shows the right kidney ultrasound with UTD P3. A VCUG showed no reflux. The renogram at 6 weeks of age showed that the right kidney contributed 35% and the left contributed 65% to the total renal function. Following administration of furosemide, poor drainage was noted on the right side. The patient returned at that time for a review of the renal scan, and a second renal sonogram showed a slight improvement in the hydronephrosis (Figure 2B); therefore, surgery was not recommended. A renal sonogram at approximately 3 months showed definite improvement in the degree of right hydronephrosis (Figure 2C). At 1 year, a renal ultrasound showed almost complete resolution of the severe hydronephrosis with decompression of the collecting system (Figure 2D).
Antenatal hydronephrosis (ANH) is observed in 1% to 2% of all pregnancies and is one of the most common congenital abnormalities.1 The estimated birth rate of 4 million/year in the United States means about 40,000 to 80,000 children are diagnosed annually with ANH.1
Prenatal diagnosis of hydronephrosis provides the opportunity to avoid febrile urinary tract infections in infants and young children and allows for early intervention in cases with poor renal function associated with severe hydronephrosis and concomitant compression of renal parenchyma.2 Although nephrogenesis is complete by 36 weeks’ gestation, the effect of significant obstruction on ultimate healthy nephron endowment is unknown.
The differential diagnosis includes transient hydronephrosis (most common cause), ureteropelvic junction obstruction, ureterovesical junction obstruction or primary obstructed megaureter, vesicoureteral reflux, multicystic dysplastic kidney, ureterocele, and ectopic ureter with and without renal duplication, and posterior urethral valves.2 Significant obstruction is more commonly associated with progressive, rather than stable or improved, dilation prenatally.
The prenatal sonogram is usually performed in the second trimester (16-20 wk) and again in the third trimester (28-32 wk).2 The prenatal sonogram provides information including the APRPD measured on transverse image at the maximal diameter of the intrarenal pelvis, renal parenchymal thickness and echogenicity (when compared with the liver or spleen), corticomedullary differentiation and cortical cysts, calyceal dilation of major and minor calyces, ureteral dilation, bladder wall thickening, and presence of a ureterocele or dilated posterior urethra. The National Institute of Child Health and Human Development’s 2014 Executive Summary on Fetal Imaging defined an abnormal APRPD as (1) ≥ 4 mm in the second trimester, and (2) ≥ 7 mm at ≥ 32 weeks with postnatal radiographic evaluation recommended.3
A unified classification system with standard terminology has recently been developed for the diagnosis and management of prenatal and postnatal UTD. This system integrates the current grading systems, including the grading system of the Society for Fetal Urology. Figures 3 and 4 show the UTD risk stratification prenatally and postnatally, respectively.2
Classification between low and increased risk (Figure 3]) is based on the presence of any increased risk parameters. For example, a fetus with an APRPD within the UTD A1 range but with peripheral calyceal dilation is classified as UTD A2-3.2 The findings of renal pelvic dilation may vary depending on the degree of pelvic distention and fetal hydration at the time of the study. Pyelectasis on a mid-trimester prenatal ultrasound has been related to trisomy 21, but, as an isolated observation, carries an odds ratio of 1.5 to 1.6 for Down syndrome.4 Ureteral dilation observed prenatally is classified as UTD A2-3 regardless of the APRPD findings.2
Stratification into intermediate risk and high risk (Figure 4) is based on the most concerning postnatal ultrasound finding. For example, if the APRPD is in the UTD P1 range, but there is peripheral calyceal dilation, the classification is UTD P2. Similarly, the presence of parenchymal abnormalities makes the classification UTD P3, regardless of APRPD measurement.2 Stratification of risk for bilateral involvement is based on the grading of the UTD of the more severely affected renal unit.2 Ureteral dilation observed postnatally is assigned category UTD P2 regardless of the APRPD findings.2
The timing of the first postnatal sonogram remains controversial and should be individualized. It is recognized that because of the infant’s physiologic dehydrated status, a sonogram performed within the first 48 hours will likely underestimate the degree of dilation observed prenatally. This dehydration also affects bladder distention during the study. If the study is performed at <48 hours, a follow-up study must be performed. Usually, the first postnatal ultrasound is performed between > 48 hours and < 4 weeks of age, unless posterior urethral valves are suspected or bilateral ANH was observed.2 The timing of the first study and of subsequent evaluations is dictated by the degree of ANH, the findings on the first postnatal study, and parental concerns. In patients with low-risk UTD P1, a second ultrasound should be performed at 1 to 6 months, whereas patients with UTD P2 should be reimaged at 1 to 3 months.
Continuous antibiotic prophylaxis remains controversial and is administered at the discretion of the clinician. Antibiotics are recommended for neonates and infants with UTD P3 who will also undergo a VCUG.2 Administration of amoxicillin at the time of the VCUG is recommended.
A VCUG is recommended for significant hydronephrosis (UTD P3—although the degree of hydronephrosis does not correlate with the grade of reflux), ureteral dilation, or other findings pre- and postnatally (eg, abnormal parenchymal thickness or appearance, bladder wall thickening).2 Whether or not the VCUG is performed, it is imperative that parents be educated on the signs and symptoms of a urinary tract infection in neonates and infants. These include fever (usually observed after the first month of life), poor feeding (“skipping a meal”), excessive irritability, and listlessness.
A renogram is recommended for some patients with UTD P2 and for all patients with UTD P3 during the second month of life, as by this time the glomerular filtration rate has doubled.2 Findings of poor function (< 40%) and poor to no demonstrable drainage are indicative of significant obstruction. These, in addition to a history of progressive increase in fetal renal pelvic dilation during gestation, suggest the need for intervention.5 Delaying surgery with close follow-up is not necessarily wrong, but, as one observes compressed pyramids and corticalparenchyma, it is obvious that kidney function is compromised; whether this affects ultimate healthy nephron endowment is unknown. It is also unknown whether function in a presumed obstructed kidney can always be completely recovered. The key is to intervene before the time of irreparable renal damage, because surgery by a skilled surgeon has been proven to be very effective, whether performed via the open or the robot-assisted laparoscopic approach.
