What are pituitary tumours?

The pituitary is a small gland with 2 parts at the base of the brain. It produces hormones that regulate the production of hormones in other glands.

Pituitary tumours can produce effects throughout the body because they can increase or decrease production of any of these hormones.

Pituitary tumours include:

Pituitary adenomas

Almost all pituitary tumours are benign adenomas that tend to grow slowly over many years.

Macroadenomas

Are larger than 1 cm and can cause problems by pressing on healthy pituitary tissue, the optic nerve, or other brain structures, or by over-secreting hormones.

Microadenomas

Are smaller than 1 cm, rarely large enough to damage neighbouring structures, but can produce symptoms by affecting hormone production.1 As brain scans have become more widely used, results have suggested that perhaps one in 4 people have pituitary adenomas but many go unnoticed, particularly if they are non-secreting microadenomas. 

Pituitary carcinomas

Are extremely rare pituitary tumours, usually fatal, and appear very similar to adenomas. Some are only identified with hindsight when a tumour that was thought to be an adenoma starts to spread, causing secondary tumours elsewhere in the body.

Pituitary tumours that over-secrete hormones

Many larger pituitary tumours secrete hormones in excessive quantities: they are often diagnosed following blood tests that reveal high circulating hormone levels.

Anterior pituitary tumours

Pituitary tumours that secrete hormones usually form in the larger part of the gland, the anterior pituitary. Tumours can increase production of:

Growth hormone

In childhood and adolescence this can lead to gigantism and in later life, it can cause acromegaly.

Prolactin

The hormone that stimulates breasts to produce milk. Prolactin-secreting tumours are the most common type of pituitary tumour. Women with such tumours stop menstruating and can start producing milk. Younger women often experience infertility. Men with prolactin-secreting pituitary tumours often become impotent.

Thyroid-Stimulating Hormones (TSH)

Stimulate the thyroid gland and regulate metabolism. TSH secreting tumours are very rare and cause symptoms such as shaking, rapid heartbeat and anxiety.

Adrenocorticotropic hormone (ACTH)

Stimulates the production of hormones from the adrenal gland. ACTH secreting pituitary tumours can cause Cushing’s disease.

Luteinizing hormone and follicle-stimulating hormone

Regulate the ovaries and stimulate the production of oestrogen and progesterone in women. In men, they control testosterone and sperm production. Such tumours can affect the menstrual cycle and can lead to infertility.

Posterior pituitary tumours

These can over-produce:

• Vasopressin (antidiuretic hormone), which regulates water retention by the kidneys. Tumours here are rare but damage to this part of the pituitary, by pressure from a tumour nearby, for example, can lead to diabetes insipidus
• Oxytocin causes the uterus to contract during childbirth and stimulates milk production. Tumours that produce oxytocin are very rare

Pituitary tumours and hormone deficiency

Pituitary tumours, particularly macroadenomas and pituitary carcinomas, can also lead to hormone deficiencies by preventing growth and normal function of healthy pituitary tissue producing symptoms that may include:

• Nausea
• Weakness
• Weight changes
• No menstruation (in women of child-bearing age)

• Men may have trouble getting and maintaining an erection

Pituitary tumours: other effects

Hormone secreting and non-secreting pituitary tumours can cause neurological damage as they grow and press on other brain tissue, leading to:

• Headaches and sight problems, including loss of peripheral vision, eye paralysis, and blindness as the tumour presses on the nearby optic nerve
• Facial pain or the sensation of numbness
• Feeling faint or dizzy

Pituitary tumours that grow into the neighbouring hypothalamus can produce problems with thirst, appetite, temperature regulation and consciousness.