Biliary mucinous cystic neoplasm, low-grade (cystadenoma) and high-grade (cystadenomarcinoma)

(A) Mucinous cystic neoplasm, low-grade (cystadenoma) showing bland neoplastic epithelial cells (arrow) and underlying compact spindle-cell "ovarian-type" stroma (arrowheads).
(B) Mucinous cystic neoplasm, high-grade (cystadenocarcinoma) composed of multiloculated cysts (arrows) that are lined by pleomorphic neoplastic cells with cribriform pattern.