What can go wrong?
The most common problem with the pituitary is the development of a tumour. While most tumours are benign, they can produce excessive amounts of a specific pituitary hormone, crowd out the production of other hormones and compress surrounding tissues. Blood vessels and the optic nerves are in close proximity to the pituitary gland, and pressure from a tumour can cause headaches, visual disturbances, loss of vision, fatigue, weakness and seizures, as well as a host of signs and symptoms related to diminished hormone production.
Other pituitary disorders can arise from inherited genetic mutations; others are congenital, due to trauma or an impaired blood supply, due to surgical or radiation treatment of a previous pituitary disorder, due to a malignant tumour (rare), or due to causes that are not yet well understood. The hormone deficiencies and excesses from these disorders can produce a variety of symptoms depending on which hormones and target tissues are affected.
When the hypothalamus is dysfunctional, pituitary hormone production is often affected. Excess or deficient hormone production by the pituitary may also occur if the glands ‘downstream’ from it are dysfunctional. For example, the hypothalamus normally detects thyroid hormone deficiency in the blood and stimulates the pituitary to produce TSH. TSH, in turn, stimulates thyroid hormone production by the thyroid gland. If the thyroid gland is dysfunctional and cannot produce adequate amounts of this hormone, blood thyroid hormone levels will remain below normal even though the hypothalamus and pituitary are promoting production. The result is excessive amounts of TSH and deficient thyroid hormone.
Examples of common pituitary disorders
- Pituitary tumours. These may be hormone-secreting or non-secreting tumours and they are benign. They may cause visual disturbances and headaches as they grow and compress surrounding tissues, and they often result in excessive amounts of one pituitary hormone and decreasing amounts of the other hormones.
- Growth hormone deficiency. This has a variety of causes. In children, it causes delayed growth and short stature; in adults, it can lead to muscular weakness, fatigue, decreased bone mass and obesity.
- Hypopituitarism. This has a variety of causes, including tumours, trauma, decreased pituitary blood supply, infection, sarcoidosis, an autoimmune process, radiation, surgical removal of the pituitary, or a side effect of pituitary surgery. It results in a general decrease in pituitary hormone production.
- Hyperprolactinaemia. This is either a pituitary tumour that secretes prolactin or a tumour that prevents the regulation of prolactin production. It can cause galactorrhoea, amenorrhoea, and decreased sex drive in men.
- Empty sella syndrome. The sella (which is the structure that surrounds the pituitary gland) may increase in size and put pressure on the pituitary gland. In rare cases, the gland shrinks and hormone production decreases, leading to hypopituitarism.
Examples of rare pituitary disorders
- Acromegaly and gigantism. This results in excess growth hormone production, usually due to a tumour. When it occurs in childhood, it causes gigantism associated with excessive bone growth and abnormally tall stature; in adults, it causes acromegaly, increased bone thickness, coarsened facial features, enlarged hands and feet, carpal tunnel syndrome, headaches, sweating, sleep apnoea, fatigue and hypertension.
- Cushing’s disease. The symptoms of Cushing’s syndrome are caused by a pituitary tumour that produces excess ACTH, which leads to excess exposure to cotisol (the adrenal gland hormone). Symptoms vary, but they include: upper body obesity, a rounded face, thin skin, pink streaks on the abdomen, muscular weakness, osteoporosis, high blood sugar, and high blood pressure.
- Diabetes insipidus. This is caused by decreased production of ADH by the hypothalamus. The patient’s kidneys do not conserve water and concentrate urine, meaning that the patient is thirsty and has frequent dilute urination.
- Nelson’s syndrome. A pituitary tumour develops that produces ACTH and can cause darkening of the skin. Patients may develop this syndrome when adrenal glands are removed as part of the treatment for Cushing’s disease.
- Multiple endocrine neoplasia Type 1 (MEN1). This is an inherited genetic mutation that increases the risk of developing tumours in the pituitary.
- Kallman syndrome. A deficient release of GnRH (gonadotropin-releasing hormone) leads to a lack of FSH and LH production, which causes delayed or absent puberty. It is associated with no sense of smell and occurs only in males.
- Pituitary infarction. This results in restricted blood supply to the pituitary gland, which may cause gland tissue damage and lead to hypopituitarism.
- Sheehan syndrome. The pituitary gland increases in size during pregnancy, which can cause pituitary infarction if there is an acute drop in blood pressure during childbirth.
- Craniopharyngioma. This is the most common tumour that develops close to the pituitary gland in children. It is benign but it may put pressure on the pituitary, causing hypopituitarism, headaches, visual disturbances and delayed growth.