Amorphous and stellate amyloid in functioning human pituitary adenomas: histochemical, immunohistochemical and electron microscopic studies.

Two types of amyloid, amorphous and stellate, were studied in 3 functioning human pituitary adenomas (2 prolactin-secreting and one growth hormone (GH) secreting) by histochemical and immunohistochemical techniques and by electron microscopy. The amorphous amyloid was found in all 3 adenomas, but the stellate type was observed only in the Gh-secreting tumor. Both types of deposits satisfied the staining characteristics of amyloid and were composed of aggregated filaments, 30-300 A in diameter by electron microscopy. The stellate type was strongly positive for GH by immunohistochemistry and showed ultrastructural transition to surrounding tumor cells, findings strongly suggestive of a hormonal origin. The presence of scattered secretory granules in the amorphous type was correlated with weak immunostaining for prolactin in the amyloid.