A 29-year-old woman, gravida 1 para 0, at 21 weeks gestation comes to the office for a fetal anatomy ultrasound. She feels well and has had no vaginal bleeding, leakage of fluid, or contractions, but she has not yet felt any fetal movement. The patient has no chronic medical conditions and her pregnancy has been uncomplicated. Vital signs are normal. Ultrasound reveals minimal amniotic fluid, consistent with oligohydramnios. A singleton male fetus is in the breech presentation. Fetal heart rate is 170/min. Fetal lungs appear hypoplastic and have no surrounding pleural fluid bilaterally. The fetal abdomen has a large fluid-filled mass arising from the pelvis, consistent with a distended bladder. Bilateral fetal kidneys are enlarged and have thin renal cortices. Which of the following is the most likely underlying cause of these ultrasound findings?

Question

A 29-year-old woman, gravida 1 para 0, at 21 weeks gestation comes to the office for a fetal anatomy ultrasound.  She feels well and has had no vaginal bleeding, leakage of fluid, or contractions, but she has not yet felt any fetal movement.  The patient has no chronic medical conditions and her pregnancy has been uncomplicated.  Vital signs are normal.  Ultrasound reveals minimal amniotic fluid, consistent with oligohydramnios.  A singleton male fetus is in the breech presentation.  Fetal heart rate is 170/min.  Fetal lungs appear hypoplastic and have no surrounding pleural fluid bilaterally.  The fetal abdomen has a large fluid-filled mass arising from the pelvis, consistent with a distended bladder.  Bilateral fetal kidneys are enlarged and have thin renal cortices.  Which of the following is the most likely underlying cause of these ultrasound findings?

Quizplus · Accepted Answer

Explanation: 11ec25c8_da5c_6d69_bc81_359d87f87d2b_MD0003_00 This fetus has posterior urethral valves (PUV), a congenital disorder commonly diagnosed on prenatal ultrasound. PUV is the result of abnormal, persistent urethral folds that cause bladder outlet obstruction in males resulting in: prenatal ultrasound urinary obstruction, leading to a dilated posterior urethra and bladder distension (eg, fluid-filled abdominal mass). With increasing backup of urine, hydronephrosis may develop (eg, enlarged kidneys with thin renal cortices). decreased fetal urine output and subsequent oligohydramnios, as amniotic fluid is primarily composed of fetal urine. Therefore, conditions that decrease urine production or output (ie, obstruction) result in low amniotic fluid. Prolonged and early-onset oligohydramnios, as seen in this fetus at 21 weeks gestation, is associated with high morbidity and mortality. The most significant sequela is pulmonary hypoplasia (ie, neonatal respiratory syndrome) because amniotic fluid is required for fetal lung development. Additional complications include flat facies and limb deformities (ie, Potter sequence). Treatment of PUV may include fetal surgery; however, prognosis is typically poor. Potter sequence (Choice A) Bilateral renal agenesis is also associated with oligohydramnios and hypoplastic lungs; however, ultrasound would reveal absent (rather than enlarged) kidneys and a small (rather than distended) bladder. (Choices B and G) Duodenal atresia and tracheoesophageal fistula cause polyhydramnios because fetuses with these anomalies cannot completely ingest, and thereby remove, amniotic fluid via the gastrointestinal tract. This fetus has oligohydramnios. tracheoesophageal fistula (Choice C) Neuroblastoma is a common pediatric cancer that may present as an adrenal mass overlying the kidney. However, it is a solid (not fluid-filled) mass that typically does not cause bladder outlet obstruction. (Choice D) Nonimmune fetal hydrops is due to a variety of etiologies that cause excessive fluid accumulation in fetal interstitial tissues (ie, third spacing). Affected fetuses typically present with polyhydramnios and effusions (eg, pericardial, pleural), rather than oligohydramnios and hypoplastic lungs with no surrounding pleural fluid. fetal hydrops (Choice E) Polycystic kidney disease may result in enlarged kidneys and oligohydramnios due to abnormally functioning fetal kidneys. However, affected fetuses would have a small-to-normal-sized bladder due to decreased urine production (rather than obstruction). Educational objective: Posterior urethral valves is a congenital disorder resulting from persistent urethral folds that cause bladder outlet obstruction. Most cases are diagnosed via prenatal ultrasound by signs of urinary obstruction, including bladder distension and hydronephrosis. Significant obstruction can result in an increased risk of fetal morbidity and mortality because oligohydramnios (from decreased urine output) can cause pulmonary hypoplasia. References: Ultrasound diagnosis of fetal renal abnormalities. (http://www.ncbi.nlm.nih.gov/pubmed/24524801) Fetal bladder outlet obstruction: embryopathology, in utero intervention and outcome. (http://www.ncbi.nlm.nih.gov/pubmed/27570093)

A 29-Year-Old Woman, Gravida 1 Para 0, at 21 Weeks