A fetus shows severe oligohydramnios, pulmonary hypoplasia, and bilateral flank masses with absent renal tissue on antenatal ultrasound. The defect lies in failure of which structure to induce the surrounding mesoderm?
- A Wolffian duct
- B Ureteric bud ✓
- C Allantois
- D Yolk sac
Correct answer: B. Ureteric bud
Explanation
Bilateral renal agenesis results when the ureteric bud fails to reach or induce the metanephric blastema, so nephrons never form. The resulting absence of fetal urine causes oligohydramnios, producing the Potter sequence: pulmonary hypoplasia, flattened facies, and limb deformities. The Wolffian duct forms male genital ducts and only contributes the trigone region of the bladder, not induction of the metanephric mass.
Reference: Langman's Medical Embryology, 14th ed.
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