Intestinal development in insulinoma containing Psammoma bodies. Recapitulation of ultrastructural features.

Extensive junctional complex formation was observed between cells of an insulinoma with an acinar pattern. Cytolysosomes, multivesicular bodies, and small vesicles were present in the luminal aspect of acinar cells that were shedding cytoplasm. These and other ultrastructural features suggest a recapitulation of intestinal development by this tumor and this is consistent with an endodermal origin of pancreatic beta-cells or their precursors. Psammoma body formation, a rare occurrence in apudomas, was probably due to the accumulation of intraluminal cytoplasmic debris.