A newborn boy is evaluated for respiratory distress shortly after delivery. He was born at an estimated 37 weeks gestation via spontaneous vaginal delivery to a 20-year-old primigravid mother who had no prenatal care. The mother has no chronic medical conditions and does not use tobacco, alcohol, or illicit drugs. The boy's temperature is 36.7 C (98 F), pulse is 144/min, and respirations are 70/min. Pulse oximetry is 84% on room air. Physical examination shows flattened facies. There are intercostal retractions, and bilateral lungs have decreased aeration. The abdomen is distended, and there is a palpable, soft, suprapubic midline mass. The external male genitalia appear normal. The extremities are cyanotic, and bilateral clubfeet are present. Which of the following is the most likely underlying cause of this patient's clinical condition?

Question

A newborn boy is evaluated for respiratory distress shortly after delivery.  He was born at an estimated 37 weeks gestation via spontaneous vaginal delivery to a 20-year-old primigravid mother who had no prenatal care.  The mother has no chronic medical conditions and does not use tobacco, alcohol, or illicit drugs.  The boy's temperature is 36.7 C (98 F), pulse is 144/min, and respirations are 70/min.  Pulse oximetry is 84% on room air.  Physical examination shows flattened facies.  There are intercostal retractions, and bilateral lungs have decreased aeration.  The abdomen is distended, and there is a palpable, soft, suprapubic midline mass.  The external male genitalia appear normal.  The extremities are cyanotic, and bilateral clubfeet are present.  Which of the following is the most likely underlying cause of this patient's clinical condition?

Quizplus · Accepted Answer

11ec25c8_d72c_155b_bc81_bf849df0c1f8_MD0003_00 This newborn with respiratory distress has hypoxia with decreased lung aeration (suggestive of pulmonary hypoplasia), flattened facies, and limb deformities. This constellation of findings, known as , represents the pathophysiologic manifestations of any condition associated with inadequate amniotic fluid levels (eg, urinary tract obstruction, renal agenesis, polycystic kidney disease, preterm premature rupture of membranes). This patient's abdominal distension and suprapubic mass are consistent with bladder distension resulting from urinary tract obstruction. In newborn boys, this is most commonly due to . In patients with PUV, abnormal folds in the posterior urethra (eg, persistent posterior urethral membrane) obstruct urinary flow, resulting in progressive dilation of the bladder, ureters, and kidneys, which can be identified on prenatal ultrasound (and may have been missed in this patient whose mother had no prenatal care). Poor urine output (oliguria) in utero results in oligohydramnios because fetal urine is a major source of amniotic fluid. Because amniotic fluid is required for normal alveolar development, fetuses exposed to prolonged oligo- or anhydramnios are at risk for pulmonary hypoplasia, as in this case (eg, hypoxia, decreased aeration, accessory muscle use, cyanosis). Low amniotic fluid also restricts fetal movement, leading to a cascade of physical anomalies, including flat facies and positional limb deformities (eg, clubfeet, hip dislocation). dilation of the bladder, ureters, and kidneys In addition to a suprapubic mass (ie, distended bladder), neonates with PUV may also have weak urinary stream and renal failure postnatally due to obstructive uropathy. (Choice A) Congenital diaphragmatic hernia (CDH) is a life-threatening defect of the diaphragm that allows abdominal viscera to herniate into the chest, restricting lung development. The abdomen appears scaphoid, and a barrel-shaped chest due to the presence of abdominal contents is seen, not an abdominal mass. Although some cases of CDH are associated with other anomalies, flat facies and clubfeet are more consistent with fetal constraint due to Potter sequence. (Choice B) Duodenal atresia obstructs fetal reabsorption of amniotic fluid, leading to polyhydramnios. Polyhydramnios, or excessive amniotic fluid, does not cause signs of fetal constraint (eg, flat facies, clubfeet), as in this case. In addition, a suprapubic midline mass would not be expected. (Choice C) Hypospadias (ventrally displaced urethral meatus) is typically an isolated finding and not associated with urinary obstruction or Potter sequence. In addition, this patient has normal external male genitalia. (Choice E) Transient tachypnea of the newborn presents in the first few hours of life with respiratory distress due to retained fetal lung fluid. An abdominal mass, flattened facies, and limb abnormalities are not seen. (Choice F) Wilms tumor is the most common renal malignancy in childhood and can present with an abdominal mass. Wilms tumor is rare in the neonatal period and is not associated with Potter sequence. Educational objective: Posterior urethral valves are the most common cause of urinary tract obstruction in newborn boys. Oligohydramnios from urinary obstruction can lead to Potter sequence, which is characterized by pulmonary hypoplasia, flat facies, and limb deformities. References: Posterior urethral valve. (http://www.ncbi.nlm.nih.gov/pubmed/21822988)

A Newborn Boy Is Evaluated for Respiratory Distress Shortly After