Fig. 1.

SBT with hierarchically branched papillae (a) covered by a single-layered or multilayered epithelium with pseudopapillary proliferations and secretory or ciliated serous differentiation (b). Micropapillary SBT demonstrates non-hierarchical “Medusa-like” branching and a more cellular stroma (c). Its epithelium is more cuboidal with “nuclear atypia greater than that allowed for conventional SBT” and often containing small nucleoli (d). Some micropapillary SBTs have a predominant cribriform epithelial proliferation (e). Microinvasion is characterized by small epithelial cell groups surrounded by retraction artifacts within a cell-rich fibroblastic stroma (f)