Pituitary gland disorders

Inborn or acquired abnormalities in the structure or function of the human pituitary gland. Pituitary disorders can stem from any of five disease processes: tumors and other growths, intrinsic lesions of the anterior lobe, diseases affecting gland function, hypothalamic malfunction, and systemic disease that affects the adenohypophysis.

Tumors and other growths in and near the pituitary may cause failure of hormone secretion or impinge on nearby brain structures. The latter effect can give rise to neurological malfunctions, the most common of which is visual impairment such as narrowing of the visual fields. Intrinsic lesions of the anterior pituitary, usually benign, secrete excessive amounts of a single (rarely multiple) hormone, producing characteristic endocrine syndromes, the most dramatic of which are acromegaly and Cushing's disease. Infections, congenital anomalies, granulomas, vascular disorders, and, rarely, metastatic cancers may induce partial or total failure of one or more pituitary secretions, in which case growth hormone, follicle-stimulating hormone, and luteinizing hormone are the first to fail.

Diseases of the hypothalamus affect pituitary function through the mechanical effects of a mass or through disrupted secretion of the hypophysiotropic peptides. Typical manifestations include precocious or delayed puberty; diabetes insipidus; and derangements of sleep, eating, and temperature regulation. The dysfunction may be of congenital, traumatic, inflammatory, or neoplastic origin. However, the most important hypothalamic-pituitary diseases are tertiary hypothyroidism, precocious or delayed puberty, diabetes insipidus, and Kallmann's syndrome, which consists of a deficient sense of smell and lack of sexual development due to inborn failure of the hypothalamus to secrete gonadotropin-releasing hormone. Hypothalamic disorders can cause abnormalities of growth hormone secretion. Whereas most individuals with acromegaly (an excess of growth hormone) have intrinsic pituitary tumors that secrete growth hormone, some have excessive secretion of hypothalamic growth hormone-releasing hormone or insufficient secretion of somatostatin. Pituitary dwarfism, caused by the failure to secrete growth hormone in childhood, is usually due to primary disease of the adenohypophysis, but in some individuals the fundamental dysfunction (opposite to that in acromegaly) lies in the hypothalamus. See also Diabetes; Dwarfism and gigantism; Somatostatin.

The adenohypophysis can be affected subtly by systemic diseases, or more obviously by metastases from breast cancer. Prolonged treatment with large doses of adrenal corticosteroids, as in cases of lupus, asthma, or acute leukemia, can result in the failure of the adenohypophysis to secrete adrenocorticotropic hormone in times of physical stress. A deficiency in adrenocorticotropic hormone is a potentially fatal condition. See also Adenohypophysis hormone; Adrenal gland disorders; Pituitary gland.