CHAPTER 11 Urological Emergencies in the Newborn
How often does prenatal sonography detect a significant fetal anomaly?
In 1% of pregnancies.
How many of these are genitourinary, and what is the most common urologic abnormality?
Twenty-five percent are genitourinary. Hydronephrosis is the most common urologic abnormality found on sonography, representing 50% of all genitourinary fetal anomalies.
What is the significance of bilateral hydronephrosis?
This may indicate vesicoureteral reflux (VUR), fetal ureteral folds, or megaureters. Posterior urethral valve (PUV) must also be considered in a male fetus, especially if there is evidence of a dilated bladder.
What is the cause and significance of oligohydramnios?
Abnormal or deficient fetal kidneys will produce less urine, which leads to oligohydramnios. Therefore, a screening ultrasound evaluation of the fetal kidneys is reasonable if oligohydramnios is found. Oligohydramnios may also be caused by rupture of amniotic membranes, inadequate urine production, obstructive uropathy, or post-term gestation. Renal causes of oligohydramnios include renal agenesis or dysplasia, obstruction, or hypoperfusion of the kidneys. Oligohydramnios may lead to pulmonary hypoplasia. The second trimester is the most critical for fetal lung maturation.
Which are potentially more dangerous: obstructive or nonobstructive lesions of the kidneys?
In association with hydronephrosis, obstructive lesions are more dangerous, especially if bilateral. However, bilateral renal dysgenesis (caused by diseases such as autosomal recessive polycystic kidney disease, multicystic dysplastic kidney) may be lethal.
Renal pelvic diameter measurements can be helpful in determining the significance of hydronephrosis. What measurements would be considered significant?
Specific measurements are somewhat controversial. An anteroposterior (AP) diameter greater than 7 mm in the second trimester and 10 mm in the third trimester are some guidelines. Smaller is better.
A distended bladder that does not empty suggests which diagnosis?
Posterior urethral valve, prune-belly syndrome, urethral atresia, or neuropathic bladder (eg, spina bifida).
Which of these is the most dangerous?
Urethral atresia has the highest mortality rate among these.
Consultation is requested for an otherwise healthy term infant with a palpable right-sided abdominal mass. Prenatal sonography was not performed. How do you proceed with your physical examination?
A general examination must begin with initial attention to subcutaneous nodules (neuroblastoma) or dehydration, particularly with hematuria (as seen in renal vein thrombosis). The patient should be placed in the lateral decubitus position for kidney palpation by supporting the flank with one hand and palpating the upper quadrant subcostally with the opposite hand. Care should be taken to avoid extensive abdominal manipulation after the initial examination to prevent the rare occurrence of rupture as seen in cases of Wilms’ tumor/mesoblastic nephroma. Transillumination of the flank mass may distinguish cystic from solid lesions. Following a complete physical examination, including careful blood pressure measurements, abdominal sonography is indicated.
A 23-year-old pregnant female presents for evaluation of prenatally detected unilateral hydronephrosis. There is no oligohydramnios. What would be your consideration and recommendation to the patient?
Prenatal fetal hydronephrosis is the most commonly diagnosed fetal urologic abnormality. While the overall incidence of hydronephrosis on prenatal sonography is between 1% and 1.5%, the incidence of clinically significant hydronephrosis is between 0.2% and 0.4%. With normal amniotic fluid levels, close follow-up throughout the pregnancy and in the neonatal/newborn period as well as through the first year of life are required. It is important to note that a postnatal ultrasound evaluation performed within the first 48 hours of life may underestimate the degree of hydronephrosis due to physiologic oliguria in the newborn. The majority of cases of prenatal low-grade hydronephrosis may stabilize and resolve within the first year of life.
This woman delivered a 7 lb, 3 oz otherwise healthy male infant. Postnatal sonography confirms the presence of unilateral hydronephrosis. What further evaluation do you recommend?
Careful physical examination with an emphasis on observing the infant’s active voiding is an important first step. The infant should be started on antibiotic prophylaxis, as the incidence of urinary tract infection (UTI) is approximately 3% to 4% in the first 6 months of life. A voiding cystourethrogram (VCUG) and nuclear renogram (DTPA or MAG 3) should also be scheduled. Nuclear renography is dependent on glomerular filtration rate (GFR) for excretion of the isotope. Neonatal GFR increases several fold during the first 2 months of life. Therefore, the optimal timing of the renal scan is during the second month of life. Recent work suggests a conservative approach to nuclear renography in patients with mild hydronephrosis.
A 32-week prenatal sonogram of a male fetus followed for hydronephrosis reveals increasing bilateral hydronephrosis, a dilated bladder, and new-onset marked oligohydramnios. What is your recommendation?
Posterior urethral valve leading to bilateral hydronephrosis with oligohydramnios is the most likely etiology, and this situation potentially represents a rare urologic indication for induction of labor or fetal intervention. Fetal lung maturity should be evaluated with a lecithin/sphingomyelin amniotic fluid ratio prior to a final recommendation. If fetal surgical intervention is considered, fetal renal function should be estimated by the urinary sodium chloride, osmolality, and β2 microglobulin obtained by fetal bladder aspiration. A high-grade obstruction of a single system also requires a similarly rapid response. The outcomes for fetal intervention with respect to improvement of renal function are mixed.
A male infant delivered at an estimated 34 weeks gestational age without prenatal care demonstrates failure to thrive and neonatal ascites. The infant is noted to have a diminished, dribbling urinary stream. What is the most likely diagnosis?
The most common cause of bladder outlet obstruction in the male newborn is a PUV. An abdominal mass, failure to thrive, and neonatal ascites are among the most common presenting symptoms. Clearly, the widespread use of prenatal sonography has directed early investigations in patients with PUV.
What prenatal sonographic findings are suggestive of a PUV, and what is the most important information needed to determine further prenatal care?
Increased bladder wall thickness on prenatal sonography may indicate outlet obstruction, and dilation of the posterior urethra (keyhole sign) is strongly suggestive of PUV. The most important information needed to determine further prenatal care is the presence and timing of onset of oligohydramnios. In the setting of oligohydramnios, increased renal echogenicity is a poor prognostic indicator. Urinary electrolytes have been shown to be a useful indicator of renal salvageability only in the setting of oligohydramnios and in early gestation (18–24 weeks).
Prenatal sonography at 22 weeks reveals bilateral hydroureteronephrosis with a distended bladder consistent with a PUV. Attempts at placement of a vesicoamniotic shunt are unsuccessful. Labor is induced at 32 weeks. What is the initial management at birth?
Recognition of prenatal hydronephrosis suggests the need for repeat sonography at birth to establish a baseline view of the renal collecting systems. When a suspicion of PUV exists, bladder catheterization should be performed and the patient should be placed on prophylactic antibiotics. A VCUG should be performed when the patient is stable. When a PUV is present, VCUG often demonstrates a thick, trabeculated bladder with a dilated posterior urethra.
A 35-week gestational age male infant with an apparent PUV on VCUG has tense abdominal distension with a fluid wave and a urine output of 0.2 mL/kg/h despite aggressive fluid resuscitation. What is the most likely diagnosis?
Neonatal urinary ascites occurs in 7% of male infants with PUV. The diagnosis is based on clinical and radiological evidence and can be confirmed by a diagnostic tap of the ascites. When bladder outlet obstruction is suspected, catheter drainage is initiated followed by drainage of ascites only if respiratory compromise is suspected.
Following ablation of PUV, difficulty passing a catheter into the bladder is encountered. What is the most likely cause?
Hypertrophied bladder neck resulting from bladder outlet obstruction.
A 32-week gestational age infant is delivered after induction of labor for oligohydramnios and hydronephrosis. A cystic mass is noted on the ventral surface of the penoscrotal junction. What finding is expected on the VCUG?
A cystic mass at the penoscrotal junction especially with dribbling urinary stream is likely the rare finding of an anterior urethral valve. VCUG will likely show a large ventral diverticulum due to a crescentic cusp on the ventral aspect of the urethra. VUR may also be seen with this condition.
What are causes of nonobstructive fetal hydronephrosis?
VUR (incidence of 15%–20% in white patients and less than 1% in black patients with prenatal hydronephrosis) and fetal ureteral folds are common causes of mild or transient ureteral dilatation noted on prenatal sonography.
A prenatal sonogram detects oligohydramnios and the presence of multiple small cysts (1–2 mm in diameter). Liver sonography demonstrates periportal fibrosis. What is the most likely diagnosis, and what is its prognosis?
Hepatic fibrosis with a polycystic kidney is consistent with autosomal recessive polycystic kidney disease of the infantile form. Postnatal sonography typically reveals bilaterally large, echogenic kidneys with poor corticomedullary differentiation. (Contrast urography would reveal severely delayed function and a nephrogram with an alternating radially oriented sunray pattern.) Infantile presentation typically leads to death by 2 months of age.
What is the most likely cause of an abdominal mass in a healthy-appearing male infant, and how can it be differentiated from the second most common cause of neonatal abdominal masses?
Hydronephrosis due to ureteropelvic junction (UPJ) obstruction is the most common cause of a neonatal abdominal mass. Multicystic dysplastic kidney (MCDK) is the second most common cause of the neonatal abdominal mass and can be distinguished from UPJ obstruction by the sonographic findings of multiple noncommunicating cysts, minimal or absent renal parenchyma, and the absence of a central large cyst. The 2 entities can also be differentiated by the 99mTc DMSA renal scan. The renal scan usually demonstrates some function in the hydronephrotic kidney and nonfunction of the MCDK.
An infant is diagnosed with a right MCDK. What is of concern regarding the contralateral kidney?
The contralateral kidney and collecting system must be carefully studied in cases of MCDK. Contralateral VUR is the most commonly encountered abnormality with an incidence of 15% to 40%. Contralateral hydronephrosis due to UPJ obstruction occurs in approximately 10% of infants with MCDK.
A 1-month-old female infant is admitted to the neonatal intensive care unit (NICU) with failure to thrive and respiratory distress. Physical examination reveals a large right-sided abdominal mass. Sonography reveals an enlarged right kidney with multiple noncommunicating cystic structures. A renal scan reveals no perfusion to the affected side and normal function of the left kidney. What treatment would you recommend?
This clinical scenario is consistent with the findings of MCDK. Symptoms including respiratory distress, failure to thrive, hypertension, or hemorrhage are indications for nephrectomy in certain cases of MCDK. However, a subset of these patients may be managed by aspiration of the dominant cyst(s), as the cystic fluid does not tend to reaccumulate. Aspiration can typically be done by sonographic guidance and may provide immediate or even long-term management.
A clinically stable, otherwise healthy term neonate is diagnosed with left MCDK by sonography. The right kidney is noted to be free of reflux with intact renal function. Is there a role for observation?
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