There are numerous causes of hypopituitarism (see Table 1). The most common cause of hypopituitarism is a pituitary tumor (also known as a pituitary adenoma ). Pituitary adenomas are almost invariably benign (not cancerous). However, the pituitary adenoma itself may put pressure on the remaining normal part of the pituitary gland and limit or even destroy its ability to produce hormones appropriately (see Figure 1) .
Figure 1. Depiction of a pituitary adenoma (dark brown) next to a normal pituitary (light brown). The normal pituitary is compressed by the tumor which may cause hypopituitarism. (reprinted with permission, from Kronenberg H, Melmed S, Polonsky K, Larsen PR (eds): Williams Textbook of Endocrinology, 11th Edition, Chapter 8, Anterior Pituitary, Melmed S and Kleinberg DL authors, Philadelphia, Penn: WB Saunders; 2008.)
Sometimes pituitary adenomas produce too much of one hormone (e.g. GH or PRL ), which is called hyperpituitarism, while simultaneously causing underproduction of other hormones produced in the adjacent normal pituitary gland. In this case, reduced levels of some hormones (e.g. hypopituitarism due to thyroid, adrenal, and sex hormone dysfunction) can be accompanied by overproduction of other hormones.
Hypopituitarism can also result from pituitary surgery. which might damage part of the normal pituitary. It can result from radiation treatment that, over time, also might damage the normal pituitary, even if the pituitary gland was working normally when the patient
was first diagnosed with the pituitary adenoma. Therefore, a full pituitary hormone assessment is required both before and after surgery or radiation treatment.
Other tumors that grow near the pituitary gland (e.g. craniopharyngioma, Rathke’s cleft cyst) can cause hypopituitarism. In addition, tumors that metastasize from cancers elsewhere in the body can spread to the pituitary gland and can lead to hypopituitarism.
Inflammation of the pituitary can also cause hypopituitarism (see Table 1). Sarcoidosis and histiocytosis are types of chronic inflammation that also can result in hypopituitarism.
Radiation that focuses on a pituitary tumor or on the whole brain can result in loss of pituitary hormone production over time. In fact, it should be an expected consequence of radiation therapy. However, it may not occur for months or even years after the treatment. Thus, regular monitoring of pituitary hormone production is essential.
Pituitary apoplexy refers to a sudden hemorrhage into a pituitary adenoma and can cause rapid onset of pituitary insufficiency. This may cause double vision and/or visual loss, feeling quite ill, and may be an emergency requiring immediate attention.
Severe head trauma, usually accompanied by coma or other neurologic problems, can also cause hypopituitarism. Approximately 15% of patients with a history of severe head trauma have been found to be GH deficient. Other hormone deficiencies may also occur after severe head trauma.
Table 1. Causes of Hypopituitarism