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 best test for confirming this infant's condition?

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 best test for confirming this infant's condition?

Quizplus · Accepted Answer

Explanation: The diagnosis of a posterior urethral valve (PUV) can be confirmed using a voiding cystourethrogram (VCUG). VCUG is performed by catheterizing the patient, injecting radiopaque dye, and obtaining images during voiding. Infants with a PUV who undergo VCUG generally have dilated bladders, and approximately 25%-50% have some degree of vesicoureteral reflux and ureteral dilation due to the severe outflow obstruction caused by the PUV. However, the diagnosis is confirmed by visualization of a dilated proximal urethra when the catheter is removed (the catheter keeps the valve open and must be removed before the end of imaging). Once PUV is confirmed by VCUG, infants should have a Foley catheter placed to temporarily relieve the obstruction. When the infant's condition is stabilized, cystoscopy allows direct visualization and ablation of the valve, which is curative. (Choice A) Most PUVs are isolated findings and are not associated with syndromes. Genetic evaluation is not required when the patient has no other anomalies, as in this case. (Choice B) Nuclear medicine tests use radioisotopes (eg, technetium, dimercaptosuccinic acid) to measure renal excretion. They are commonly used to determine the overall and relative function of diseased or obstructed kidneys. However, nuclear medicine tests do not diagnose the underlying etiology of the kidney disease. (Choice C) Renal biopsy can be used for diagnosing renal failure or renal disease of unclear etiology. However, it is not indicated when signs of obstruction are present as the primary insult is extrarenal. As a result, renal biopsy will not identify the cause. (Choice D) Renal ultrasound is a quick and noninvasive initial test for suspected genitourinary malformations. Both fetal ultrasound and postnatal renal ultrasound are very sensitive for hydronephrosis. However, postnatal renal ultrasounds are less sensitive for distal obstruction and, as a result, cannot definitively differentiate ureteropelvic junction obstruction, vesicoureteral reflux, and PUVs. Therefore, VCUG is necessary to confirm the diagnosis. Educational objective: A voiding cystourethrogram is obtained by catheterizing the patient, injecting radiopaque dye, and obtaining images during voiding. It is the test of choice for diagnosing vesicoureteral reflux and posterior urethral valves. References: Advances in uroradiologic imaging in children. (http://www.ncbi.nlm.nih.gov/pubmed/22498439)

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