Infiltrative Diseases of the Pituitary Gland

Abstract

The human pituitary gland consists of the anterior pituitary (adenohypophysis), which is embryologically derived from the stomodeum (oropharynx); and the posterior pituitary (neurohypophysis), which arises as an evagination of the diencephalon (hypothalamus). During development, these two structures migrate toward one another and become collocated within the bony sella turcica. The anterior pituitary is a composite of five distinct cell types: somatotrophs, lactotrophs, thyrotrophs, gonadotrophs, and corticotrophs. These cells synthesize and secrete, respectively, growth hormone (GH), prolactin, thyrotropin (TSH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and corticotropin (ACTH). The posterior pituitary consists of axons whose nerve cell bodies and nuclei lie within the supraoptic and paraventricular nuclei of the hypothalamus. It secretes oxytocin and vasopressin (antidiuretic hormone or ADH), both of which are synthesized in the hypothalamus and migrate to the neurohypophysis in association with carrier proteins called neurophysins. The blood supply to the anterior pituitary is predominantly from the hypophyseal portal vessels, a relatively slow flowing venous system derived from the superior hypophyseal artery. The posterior pituitary is supplied almost entirely by arterial blood from the inferior hypophyseal artery. These differences in tissue derivation or in blood flow may partly explain the predilection of some disorders to preferentially involve either the adenohypophysis or neurohypophysis.