There are various causes of hypopituitarism, including both inherited and acquired causes. The most common cause is a pituitary adenoma. Other identified causes include:
Some cases of hypopituitarism are also idiopathic; in other words, there is no clear cause for the condition.
The most common cause of hypopituitarism is a pituitary adenoma, a tumor in the pituitary gland. This causes pituitary deficiency by:
Other tumors of the brain which arise in close proximity to the pituitary gland may also cause the condition, including craniopharyngiomas and Rathke’s cleft cysts.
In the vast majority of cases, the tumor is benign. As it enlarges, however, the pituitary tissue is compressed. Progressive compression leads to pituitary damage, often resulting in a reduction in the production of pituitary hormones. This eventually produces a discernible effect on the functioning of the body, and causes symptoms.
In some cases, a pituitary adenoma is hypersecreting – it leads to the excessive production of some pituitary hormones such as growth hormone and prolactin, resulting in hyperpituitarism. This can often present alongside the deficiency of other pituitary hormones.
Severe head trauma or injuries can lead to a range of neurological symptoms, as well as those of hypopituitarism. About 15 % of patients with a history of severe head trauma have later developed significant growth hormone deficiency. Other pituitary hormones are also likely to be affected.
Individuals who have undergone brain surgery in the pituitary region are more likely to be affected by hypopituitarism.
Radiation therapy that is directed towards a pituitary tumor or the entire brain can also affect the function of the pituitary gland, leading to a reduction in the production of pituitary hormones. In many cases, symptoms of this are delayed, presenting several months or years after the treatment. For this reason, ongoing monitoring of pituitary hormone production in such patients is very useful and may be mandatory.
Genetic mutations that impair the production of pituitary hormones may also be responsible for causing hypopituitarism. For example, health conditions that affect the hypothalamus will simultaneously reduce the activity of the pituitary gland and cause hypopituitarism.
There have also been some specific gene mutations that have been linked to hypopituitarism, such as PIT1 and PROP1 gene mutations.
Infiltrative diseases that cause inflammation such as sarcoidosis, Langerhans cell histiocytosis and hemochromatosis can also cause hypopituitarism in some patients.
Conditions that are linked to infection and inflammation of the brain, such as meningitis, may also constrict the pituitary gland by fibrosis and reduction of the vascular supply, and affect its function. Hypophysitis is an autoimmune condition that causes inflammation and can also lead to hypopituitarism later.
Pituitary apoplexy refers to infarction or hemorrhage into the pituitary gland. Common causes include:
A stroke or the severe loss of blood during childbirth may drastically reduce the blood supply to the pituitary, causing necrosis or death of the pituitary gland in whole or part. The obstetric condition is known as Sheehan syndrome, or postpartum pituitary necrosis.
For some patients with hypopituitarism, the cause of the condition cannot be identified. This is referred to as idiopathic hypopituitarism.
Since the pituitary function depends directly on the hypothalamus, any condition which results in altered hypothalamic function will reflect in corresponding hypopituitarism.