The widespread use of prenatal ultrasonography has raised new questions regarding the evaluation and management of neonatal hydronephrosis. Before the use of prenatal ultrasonography, most newborn patients with hydronephrosis presented with an abdominal mass or urosepsis. Indeed, the most common cause of an abdominal mass in the newborn is a multicystic dysplastic kidney and a close second cause is an obstruction at the ureteropelvic junction. However, most cases of hydronephrosis are now being detected prenatally. Following the introduction of prenatal ultrasonography, approximately 90% of cases of ureteropelvic junction obstruction and 80% of cases of obstructed megaureter seen at the Boston Children’s Hospital between 1979 and 1985 were detected prenatally. The postnatal detection rate was not significantly different from that of the era before ultrasonography. These numbers imply that the overall detection rate in infancy for such lesions is five to ten times higher than previous rates.

The ultrasonographic appearance of the kidneys changes during gestation. The output of urine begins at approximately 12 weeks of gestation. The bladder and kidneys are first visible at 14 to 16 weeks. By 16 weeks, urine is contributing significantly to the amniotic fluid volume, and the output of urine increases. Because of these changes in urine flow and renal growth, the significance of pyelectasis in utero depends on its degree in relation to gestational age. Prenatal ultrasonography is also able to detect some cases of renal dysplasia.

Despite improving technology and technique, prenatal ultrasonography cannot be relied on for a definitive diagnosis. The accuracy of prenatal ultrasonography is operatordependent, and it is generally easier to determine that an abnormality is present than to establish a specific diagnosis. Fortunately, the need to rely on prenatal ultrasonographic findings is very limited because prenatal intervention is rarely indicated.

Because a specific diagnosis cannot be made reliably with prenatal ultrasonography, the postnatal evaluation is crucial and is guided by the spectrum of anomalies seen in patients with prenatal hydronephrosis. Most kidneys prove to be normal postnatally. The frequency of this finding depends on the criteria used to define prenatal hydronephrosis. For those with persistent hydronephrosis postnatally, the differential diagnosis includes:

Ultrasonography is usually performed in the first few days of life to detect any lesions that may require prompt intervention. These include severe bilateral obstruction or posterior urethral valves. In patients with purely unilateral prenatal hydronephrosis, the initial ultrasonography can be deferred. All infants with prenatal hydronephrosis are
placed on antibiotic prophylaxis at birth. Amoxicillin can be used for the first month, and trimethoprim/sulfamethoxazole or nitrofurantoin thereafter. Antibiotics are continued at least until the nature of the lesion is defined. A second ultrasonogram is obtained some time during the first month. This follow-up study is important, even if the findings on the neonatal ultrasonogram are normal. Urine output can be very low in the first days of life and may be inadequate to cause urinary tract dilatation proximal to a significant obstruction. Careful ultrasonography can reliably detect the presence and level of obstruction. It should also detect duplication anomalies, particularly if the degree of pyelectasis differs in the two moieties. A voiding cystourethrogram (VCUG) is also obtained to rule out vesicoureteral reflux. Further management depends on the specific entity that is diagnosed.

Undescended testis is one of the most common congenital genitourinary anomalies. The incidence of undescended testis is 3% in term infants. Many undescended testes descend spontaneously in the first months of life, and the incidence at 1 year of age is 0.8%. Boys with undescended
testes are at increased risk for the development of tumors after puberty, and the testes do not produce sperm if left in an undescended location. When the descent of a testis through the normal pathway is arrested, the testis is said to be undescended. In contrast, the rarer ectopic testis has deviated from the normal pathway of descent. Possible locations for undescended testes include:

Ectopic testes may be found in the:

Because most undescended testes are located in the inguinal canal, they can be evaluated during a clinical examination. Impalpable testes present a more challenging problem and require a more extensive evaluation. When a child presents with an undescended testis, as with any congenital anomaly, a thorough history of the pregnancy and infancy is important. The parents should also be questioned as to whether anyone has ever felt the testis. Was the undescended testis noted at birth? This is particularly important in older children, who may have a retractile testis. A prior normal location of a testis, noted either during examination by the primary care physician or by the parents, suggests that the testis is retractile. Obviously, any previous inguinal surgery is important as a possible cause of secondary testicular ascent or atrophy. Although clinical hernias are uncommon in children with an undescended testis, most have a patent processus vaginalis, and it is important to inquire about a history of hernia.

The physical examination of a child with an undescended testis is a crucial part of the evaluation. A general physical examination is performed to assess surgical risk, and anomalies such as hypospadias, mental retardation, and other central nervous system anomalies, which are sometimes associated with undescended testis, should be sought. It is essential that the child be relaxed and warm during the examination. A cold room or a child’s nervousness will exaggerate a retractile testis. Before the child is touched, the genitalia and inguinal region should be visually examined. Because the first touch may stimulate a cremasteric reflex, the best opportunity to see the testis in the scrotum is on initial inspection. A true undescended testis is often associated with a poorly developed hemiscrotum on the ipsilateral side. Placing the child in the frog leg position and gently milking from the inguinal canal to the scrotum often brings a high retractile testis down. If the testis in question can be brought down in this way and remains in the hemiscrotum without tension, then the diagnosis of retractile testis is made. Applying a small dab of liquid soap to the examining hand can reduce friction and improve sensitivity in detecting an inguinal testis. Continuous age-appropriate conversation with the patient during the examination helps keep the child relaxed and improves the likelihood of detecting a palpable testis. Ectopic sites should also be palpated if no testis is felt in the inguinal region or scrotum.

The physical examination makes it possible to distinguish between an impalpable testis, a palpable undescended testis, and a retractile testis. In equivocal cases, reexamination at a later date often clarifies the diagnosis. When serial examinations leave the question of a retractile testis versus an undescended testis uncertain, a human chorionic gonadotropin (HCG) stimulation test can be performed. A variety of regimens are used. We administer 500 to 2000 IU (depending on body size) every other day for a total of five doses. It is generally agreed that a retractile testis will “descend” in response to HCG stimulation. Some truly undescended testes may also descend in response to HCG, although the actual success rate is controversial. Reported success rates range from 6% to 70%. Most retractile testes ultimately assume a normal scrotal position. However, occasionally a retractile testis will ascend with growth. Therefore, boys with a significantly retractile testis should undergo genital exams on an annual basis.

In the case of a palpable undescended testis, no further evaluation is necessary unless other genital anomalies are present. The most important genital anomaly is hypospadias, which occurs in 5% to 10% of boys with an undescended testis. Hypospadias in association with even one undescended testis raises the possibility of intersexuality. Patients with a unilateral undescended testis and hypospadias may have mixed gonadal dysgenesis and generally exhibit a mosaic karyotype of 45,XO/46,XY. Therefore, patients with an undescended testis and hypospadias should undergo karyotyping. If both testes are undescended, particularly if they are impalpable, then congenital adrenal hyperplasia (CAH) or other less common forms of intersexuality should be considered. CAH should definitely be considered in a newborn with bilateral impalpable testes and hypospadias because it is the most common cause of ambiguous genitalia. However, it should also be considered in the absence of a hypospadias because androgenization can be severe in this disorder. The initial steps in the evaluation are karyotyping and determination of the serum 17-hydroxyprogesterone level. These can rule out the two most common causes of ambiguous genitalia— CAH and mixed gonadal dysgenesis. Rarer causes of ambiguous genitalia, such as true hermaphroditism and male pseudohermaphroditism, must be considered if the child has a normal male karyotype. However, if the only genital abnormality is bilateral cryptorchidism, then a normal male karyotype is sufficient to rule out intersexuality.

In a boy with bilateral impalpable testes, the question arises whether the testes are intra-abdominal or absent. Bilateral anorchia can be diagnosed biochemically with an HCG stimulation test. Three 1500-IU doses of HCG are administered on alternate days. If the serum testosterone level does not rise and the baseline gonadotropin levels are elevated, then the child has anorchia, and no further evaluation is necessary. If the testosterone level rises after the administration of HCG, then the child has at least one functioning testis—presumably intra-abdominal. An HCG stimulation test may be avoided in a newborn by checking a serum testosterone level, which is normally elevated in the first weeks of life. If significant levels are detected, then at least one testis must be present and an HCG stimulation test is not required.