Cross-section of term PDA. A segment of a term PDA was obtained after therapeutic surgical ligation and resection. A Van Giessen stain is shown. The lumen is widely patent. The internal elastic lamina (lamina interna, LI) is disrupted (arrow), as occurs in the normal closure of the ductus; however, few smooth muscle cells have migrated into the intima (I), and intimal cushions have not formed. M, vessel media.

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