Pituitary hyperplasia.

The morphologic study of a large number of human pituitary tissues provided conclusive evidence that hyperplasia of various adenohypophysial cell types exists. These rare lesions may serve as the underlying cause of pituitary hypersecretory syndromes. The non-neoplastic proliferation of adenohypophysial cell types may be secondary to orthotopic or ectopic oversecretion of hypothalamic regulatory peptides, such as GRH, CRH, TRH and GnRH, disturbances of dopaminergic regulation or iatrogenic factors. Histologically, adenohypophysial hyperplasia may be diffuse or nodular. The former type does not result in major alterations in pituitary architecture and may be impossible to recognize in small surgical specimens. The latter type is associated with enlargement of pituitary acini. Examination of the reticulin network, using silver staining techniques, represents useful tools in the differential diagnosis. The possible emergence of adenoma on the grounds of hyperplasia is discussed.