An 8-hour-old boy is evaluated in the neonatal intensive care unit due to respiratory distress. The infant was born at term to a 32-year-old woman, gravida 3 para 2. The mother's routine serologic screening in the first trimester was unremarkable except for a lack of antibody against rubella. The pregnancy was complicated by oligohydramnios. Antenatal sonography at 19 weeks gestation showed that the fetal kidneys were in the normal position but moderately dilated and that the bladder was also dilated and had a thickened wall. Growth measurements were appropriate for gestational age. The delivery was uncomplicated, but immediately after birth, the infant developed some mild respiratory distress that is now improving. Weight is 3.35 kg (7 lb 6 oz) and respirations are 70/min. The infant is tachypneic but otherwise comfortable, with no grunting or retractions. The bladder is palpable just above the suprapubic ridge. The remainder of the examination is unremarkable.
Which of the following is the most likely diagnosis in this infant?

Question

An 8-hour-old boy is evaluated in the neonatal intensive care unit due to respiratory distress.  The infant was born at term to a 32-year-old woman, gravida 3 para 2.  The mother's routine serologic screening in the first trimester was unremarkable except for a lack of antibody against rubella.  The pregnancy was complicated by oligohydramnios.  Antenatal sonography at 19 weeks gestation showed that the fetal kidneys were in the normal position but moderately dilated and that the bladder was also dilated and had a thickened wall.  Growth measurements were appropriate for gestational age.  The delivery was uncomplicated, but immediately after birth, the infant developed some mild respiratory distress that is now improving.  Weight is 3.35 kg (7 lb 6 oz) and respirations are 70/min.  The infant is tachypneic but otherwise comfortable, with no grunting or retractions.  The bladder is palpable just above the suprapubic ridge.  The remainder of the examination is unremarkable. 
Which of the following is the most likely diagnosis in this infant?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c1c3_d5bb_8f63_8f217b45b4c3_MD0005_00 This infant's palpable bladder on examination and prenatal ultrasound findings of bilateral hydronephrosis, dilated and thickened bladder, and oligohydramnios are suggestive of a posterior urethral valve (PUV). PUV is a congenital obstruction of the urethra caused by residual embryologic tissue during genitourinary development in boys. The prevalence in boys is most likely due to the fact that the majority of PUVs are caused by abnormal insertion of the wolffian ducts, which are not present in girls, into the urethra. Most cases of PUV are identified on antenatal ultrasound, which shows bilateral hydronephrosis, thickened and dilated bladder, and a dilated proximal urethra. Dilation of the bladder is highly specific for PUV as it is not caused by more common genitourinary malformations (eg, ureteropelvic junction obstruction, duplicated collecting systems, vesicoureteral reflux). If the obstruction is severe, oligohydramnios can result and lead to Potter sequence (pulmonary hypoplasia, flattened facies). Other findings include bladder distension, weak urinary stream, and recurrent urinary tract infections (UTIs). (Choice A) Autosomal recessive polycystic kidney disease is caused by mutations in the PKHD1 gene. Affected infants have numerous small renal cysts on ultrasound, which are not seen in this patient. This disease does not cause bladder dilation. (Choice B) A duplicated collecting system results from the formation of multiple ureteric buds during kidney formation. Affected children may be asymptomatic or can have recurrent UTIs or ipsilateral hydronephrosis, but bladder dilation is not present. (Choice D) Ureteropelvic junction obstruction is caused by narrowing or kinking of the ureter, causing hydronephrosis on the affected side. Infants may have recurrent UTIs. This obstruction is rarely bilateral and does not cause bladder dilation. (Choice E) Vesicoureteral reflux is caused by the abnormal flow of urine from the bladder back into the ureter during bladder contraction and can cause recurrent UTIs. It does not cause bladder dilation. Educational objective: Posterior urethral valves are found exclusively in boys and are the most common cause of severe obstructive uropathy in children. Posterior urethral valves are generally diagnosed prenatally; hallmarks include distension and thickening of the bladder and dilation of the proximal urinary system. References: Ultrasound diagnosis of fetal renal abnormalities. (http://www.ncbi.nlm.nih.gov/pubmed/24524801) Posterior urethral valves and vesicoureteral reflux: can prenatal ultrasonography distinguish between these two conditions in male fetuses? (http://www.ncbi.nlm.nih.gov/pubmed/27374758)

An 8-Hour-Old Boy Is Evaluated in the Neonatal Intensive Care