Fig. 1

Representative microscopic images of low- and high-grade biliary intraepithelial neoplasia (BilIN) arising from a choledochal cyst. (A & B) Low-grade BilIN showing a flat growth pattern, nuclear pseudostratification (B, arrow), mild nuclear enlargement, increased nuclear-to-cytoplasmic ratio, and hyperchromasia (A & B, hemotoxylin and eosin [H&E], ×400). (C & D) High-grade BilIN shows a more complex micropapillary pattern, marked nuclear atypia, and frequent mitosis (D, arrow) (C, H&E, ×200; D, H&E, ×400)