After birth, the ductus arteriosus becomes ligamentum arteriosum and the foramen ovale becomes fossa ovalis. Which combination correctly pairs these structures?

• A. Ligamentum arteriosum; fossa ovalis
• B. Ductus venosus; septum primum
• C. Ligamentum teres; coronary sinus
• D. Fossa ovalis; crista terminalis

Answer: (A)

Postnatal remodeling of fetal shunts leaves fibrous remnants that mark where those vessels once were. The ductus arteriosus, which connects the pulmonary artery to the aorta in the fetus, closes after birth as oxygen rises and prostaglandin levels fall, turning into a fibrous cord called the ligamentum arteriosum. The foramen ovale, an opening in the interatrial septum allowing blood to bypass the nonfunctional lungs, also closes when left atrial pressure rises after birth, leaving a small scar known as the fossa ovalis. So the correct pairing is the ligamentum arteriosum as the remnant of the ductus arteriosus and the fossa ovalis as the remnant of the foramen ovale. Other options mix remnants that belong to different fetal structures (for example, the ductus venosus becomes ligamentum venosum, and the ligamentum teres comes from the umbilical vein), so they don’t fit these two postnatal remnants.