MORPHOLOGY OF PROLACTIN PRODUCING ADENOMAS

SUMMARY Prolactin cell adenomas, not uncommonly found among tumours arising from the human pituitary gland, are regarded as representing a distinct pathological entity. They can be separated into three types: (1) densely granulated prolactin cell adenomas; (2) sparsely granulated prolactin cell adenomas; (3) mixed adenomas; consisting of prolactin cells and of growth hormone cells. By light microscopy, using conventional staining procedures, prolactin cell tumours correspond to acidophilic‐chromophobic adenomas and cannot be distinguished reliably from other adenoma types. Positive cytoplasmic staining of adenomatous prolactin cells can often be obtained by Herlant's eryfhrosin or by Brookes’carmoisine methods. Immunoperoxidase technique reveals the presence of immunoreactive prolactin in the cytoplasm of adenoma cells. By electron microscopy, densely granulated adenomatous prolactin cells closely resemble resting prolactin cells seen in the non‐tumorous pituitary. Decrease in size and number of secretory granules, proliferation of rough‐surfaced endoplasmic reticulum membranes, formation of Nebenkerns, prominence of Golgi complex, presence of misplaced exocytosis are characteristic fine structural features of sparsely granulated adenomatous prolactin cells. Although more work is required to correlate structure with secretory activity, it is justified to conclude that morphologic features of prolactin cell adenomas are sufficiently distinctive to permit their identification. Immunostaining and electron microscopy are valuable techniques revealing the cell type from which pituitary adenomas derive.