In general, most endocrine pathology involves either the overproduction or the underproduction of a hormone. Overproduction of a given hormone may be caused by hyperplasia of the organ that produces the hormone, by a neoplastic process, or by some combination of the two processes. Underproduction of a given hormone, in contrast, may be caused by either destruction of the gland that produces the hormone or by conditions that deprive an endocrine organ of its normal trophic influence.
A working knowledge of the pathways that regulate normal hormone levels helps to interpret the laboratory values in patients being worked up for suspected endocrine disorders. For example, thyroid-releasing hormone (TRH) released by the hypothalamus stimulates thyroid-stimulating hormone (TSH) production by the pituitary gland, which in turn stimulates triiodothyronine (T3) and thyroxine (T4) production by the thyroid gland. T3 and T4 then cause feedback inhibition of pituitary release of TSH. If the patient has a TSH-secreting pituitary adenoma, T4 and T3 levels as well as the TSH will be high; normally, high T3 and T4 levels should cause a low TSH level. Also, remember primary diseases are diseases that originate within the gland in question (e.g., primary hyperthyroidism is due to a defect in the thyroid gland), and secondary diseases represent change in one organ as a result of disease in another organ (e.g., secondary hyperthyroidism may be due to a TSH-secreting pituitary adenoma).
This chapter will discuss diseases of the pituitary gland (hyperpituitarism, hypopituitarism, mass effect as related to pituitary gland lesions, and posterior pituitary gland pathology), diseases of the thyroid gland (goiter, hyperthyroidism, hypothyroidism, thyroiditis, and thyroid neoplasms), diseases of the parathyroid glands (hyperparathyroidism and hypoparathyroidism), diabetes mellitus, diseases of the adrenal glands (hyperadrenalism hypoadrenalism, hyperaldosteronism, and adrenal neoplasms), and multiple endocrine neoplasia (MEN).
Overview: Overproduction of pituitary gland hormones, usually referring to those derived from the anterior pituitary gland. Causes of hyperpituitarism include adenomas, hyperplasia, and carcinoma.
Epidemiology: Most pituitary adenomas occur during the fourth to sixth decades of life. Adenomas are the most common cause of hyperpituitarism.
Pituitary adenoma. This large pituitary adenoma was an incidental finding at autopsy. As would be suggested by the size of the tumor, this pituitary adenoma did not secrete any hormones (i.e., a null adenoma).
- About 30% of pituitary adenomas produce prolactin. The second most common hormone produced by adenomas is growth hormone (GH), followed by adrenocorticotropin hormone (ACTH). Thyroid-stimulating hormone (TSH) is rarely produced by adenomas. Adenomas that secrete combinations of different hormones are referred to as plurihormonal adenomas. Adenomas producing both prolactin and GH are the most common type of such mixed tumors.
- Null cell adenomas are tumors that ...