Amyloid formation in prolactinoma.

Amyloid deposits within a prolactin-secreting pituitary adenoma were investigated with light and electron microscopy. The appearance of amyloid with Congo red revealed amorphous and round green-yellow birefringence under polarized light. Spheroidal concretions disclosed prolactin-positive areas by immunohistochemistry. The amyloid commonly exhibited a structure of fine fibrils of 10 to 13 nm in width, with a hollow core. The fibrils were usually grouped in compact, stout bundles. Some bundles were present in extracellular space, others were obviously within the adenoma cells. Extracellular amyloid fibrils frequently gathered in a stellate arrangement to make a round body. The presence of intracellular amyloid fibrils in adenoma cells may represent that the source of the amyloid is neoplastic cells rather than mesenchymal cells. In addition, prolactin-positive parts in round bodies presumably exemplify that the amyloid fibrils are formed by hormone-relating proteins.