A non-epithelial pseudosarcomatous mural nodule in a mucinous cystic neoplasm of the pancreas: Immunohistochemistry, electron microscopy, and imaging studies

A mucinous cystic neoplasm of indeterminate malignant potential was found to have a well-circumscribed, 3.1 cm pseudosarcomatous mural nodule, similar to those previously described in the ovary. The nodule contained reactive giant cells and intermediate to large-sized tumor cells with bizarre mitotic figures and nuclear atypia. The tumor cells were found to be of non- epithelial origin, based on multiple negative stains for cytokeratins and ultrastructural demonstration of osteoclastic and osteoblastic differentiation and absent desmosomes. This case report is the only description of a pseudosarcomatous mural nodule in a mucinous cystic neoplasm with non-epithelial origins.