Urology for the Pediatrician



Urology for the Pediatrician


Jonathan H. Ross



HYDRONEPHROSIS IN THE NEWBORN


Etiology and Epidemiology

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.


Pathophysiology

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.


Diagnosis

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:



  • Ureteropelvic junction obstruction (the most common cause)


  • Obstructed megaureter


  • Duplication with an obstructed upper pole moiety (secondary to ureterocele or ectopic ureter)


  • Posterior urethral valves


  • Prune belly syndrome


  • Vesicoureteral reflux (may be the primary cause of hydronephrosis or associated with any of the preceding)


Treatment

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.


Obstruction of the Ureteropelvic Junction

At the first month evaluation, most patients have an obstruction of the ureteropelvic junction. The next step in the management is a diuretic renal flow scan with DTPA (diethylenetriamine penta-acetic acid) or MAG-3 (99mTcmercaptoacetyl triglycerine) to determine the degree of obstruction and relative function of the obstructed kidney. The renal flow scan can also distinguish a multicystic kidney, which does not function and appears as a photopenic region on the scan. Unobstructed or equivocal kidneys should be followed up with frequent ultrasonography during the first year of life (roughly every 3 months). In many cases, the hydronephrosis resolves. If it persists, another diuretic renal scan is obtained at 1 year. If the hydronephrosis increases during the period of observation, then the renal scan is repeated sooner than 1 year.

The appropriate management of the unequivocally obstructed kidney (defined by markedly prolonged clearance on the diuretic renal scan) is controversial. If there is decreased ipsilateral function on the renal scan, then surgical intervention is usually recommended. If there is normal ipsilateral renal function despite the obstruction, then close observation or surgical management may be undertaken.


Megaureter

Megaureter is the second most common cause of prenatal hydronephrosis. Evaluation usually consists of a renal/bladder ultrasound and voiding cystourethrography. Typical ultrasound findings are of hydroureteronephrosis with the hydroureter usually being more impressive than the intrarenal distension. Reflux should be absent on the VCUG, though, occasionally faint reflux into an obstructed ureter is seen. The use of diuretic renography is not established in evaluating washout from dilated ureters, although the analog images may be evaluated for a subjective impression of the degree of obstruction. The renal scan does offer a quantitative measurement of relative renal function. Many cases of megaureter resolve spontaneously. Surgical intervention is undertaken if hydronephrosis progresses, renal function deteriorates, or symptoms such as pain or urinary tract infection develop.


Upper Pole Hydronephrosis in a Duplicated System

Upper pole dilatation in a duplicated system is generally secondary to an ectopic ureter or ureterocele. Lower pole distension may be a consequence of secondary obstruction by an upper pole ureterocele or of vesicoureteral reflux into the lower pole moiety. These lesions can usually be well characterized by a combination of ultrasonography, renal scan, and voiding cystourethrography. In difficult cases, a magnetic resonance urogram or cystoscopy may clarify the anatomy. Surgical intervention is usually indicated, the type of surgery depending on the specifics of the individual anatomy.


Posterior Urethral Valves

Posterior urethral valves are an uncommon cause of antenatal hydronephrosis and represent one of the few entities for which prenatal intervention is occasionally indicated. The diagnosis must be considered in any male neonate with bilateral hydronephrosis. All such patients should undergo postnatal ultrasonography and voiding cystourethrography in the first few days of life. If valves are present in a term infant, they can be treated with primary valve ablation. In a preterm or ill infant, vesicostomy can be performed, with valve ablation deferred until later in life. If renal function remains poor, with persistent hydronephrosis after successful valve ablation or vesicostomy, then higher diversion by cutaneous ureterostomy or pyelostomy is considered.


Multicystic Dysplastic Kidney

The options for managing a multicystic dysplastic kidney are to remove it, follow it, or ignore it. Surgical excision is supported by reports of hypertension and malignancy (both Wilms tumor and renal cell carcinoma) in patients with multicystic kidneys. However, the number of reported cases is small, and the total number of multicystic kidneys, although unknown, is undoubtedly large. Therefore, the risk for any given patient is probably extremely small and may not justify the surgical risk of excision. Most pediatric urologists recommend following up multicystic kidneys with periodic ultrasonography and blood pressure monitoring. Obviously, any patient in whom hypertension or a renal mass developed would undergo nephrectomy.


UNDESCENDED TESTIS


Etiology and Epidemiology

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:



  • Abdomen


  • Inguinal canal (most common)


  • Superficial inguinal pouch


  • Pubic tubercle


  • High scrotum

Ectopic testes may be found in the:



  • Femoral canal


  • Perineum


  • Prepubic space


  • Contralateral scrotum


Diagnosis

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.

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Jun 29, 2016 | Posted by in PEDIATRICS | Comments Off on Urology for the Pediatrician
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