Histological classification of pituitary disease.

Morphological features of pituitary disease are classified according to increased and decreased hormone production to allow clinical correlation with pathological processes. Increased hormone synthesis and secretion may be due to pituitary adenomas or carcinomas derived from the five hormone-secreting cell types, or to extrapituitary stimuli causing hypertrophy and hyperplasia of those cells. Various tumour-like conditions can mimic functioning adenomas. Rarely, no lesion is detected and intrinsic abnormalities of adenohypophyseal cells are implicated. Hypopituitarism can be selective or generalized. Diffuse hormone deficiency is usually attributable to tissue destruction by tumours, inflammatory or infiltrative conditions or vascular lesions. Congenital abnormalities of pituitary development may result in hypophyseal dysfunction. Hypothalamic abnormalities may cause generalized hypopituitarism or may involve only selective releasing factors and hormones. Feedback inhibition and receptor abnormalities may be implicated in pituitary hypofunction, and selective deficiencies may be the result of genetic abnormalities, immune reactions or toxic damage to one cell type.