Fig. 2

a The low-power view illustrates that the surgical specimen was a well-circumscribed tumor. b, c, d The tumor consisted of mucus-filled cavities of varying sizes lined with columnar cells (b, low-power). Tall columnar cells were rich in mucous and had nuclei at the base of the cell. Some areas were stratified, protruding into the lumen and even forming branched papillary structures. Nests or papillary cell masses floated in the intracavity mucous lake accompanied by inflammatory cell infiltration (c, d high-power)