Assoc. Prof. Emma Duncan
Royal Brisbane and Women's Hospital, Brisbane.
The Pituitary Gland
The pituitary gland is a small gland about the size of a pea, situated in a bony hollow at the base of the brain, about 5 cm behind the bridge of the nose. It is one of the most important endocrine glands, because it controls hormone secretion from a number of other glands, such as the ovaries, testes (testicles), adrenal gland and thyroid.
What Can Go Wrong?
Pituitary problems can occur in both men and women, at any age. The most common abnormality of the pituitary gland is a small growth within the gland, called a tumour. Tumours in the pituitary gland are very common - between 10-25% of the population have tumours in the pituitary gland. Small tumours (less than 1cm) are called micoradenomas. Larger tumours (greater then 1cm) are called macroadenomas. Pituitary tumours are almost never cancerous.
Tumours of the pituitary gland are very common - some studies have suggested that between 10 - 25% of the population have tumours in the pituitary gland. Most often, these cause absolutely no problems at all. However, each year around 10-20 people per million in the population will have tumours in their pituitary gland that do cause problems and need help. In Australia, this means around 200-400 people a year will have a pituitary tumour that needs clinical attention. Problems can arise from both large and small tumours, depending on hormonal secretion and pressure on surrounding structures (see below).
Occasionally, pituitary problems can arise because of unusual development before birth. This can result in a craniopharyngioma or Rathke’s cleft cyst (both of these are discussed elsewhere on this website). Pituitary problems may also occur after damage to the gland. This might occur after radiation of the head, major head trauma, surgery involving the pituitary area, or other insults to the pituitary gland. Other forms of brain tumour can sometimes occur in the area of the pituitary gland also.
Pituitary problems may be suspected by a doctor after taking a history and examining a patient. To make a firm diagnosis, the doctor may do a scan of the pituitary gland (either an MRI scan or a CT scan) and organise blood tests to look at the hormones normally secreted by the gland. Vision will be looked at very carefully, as many of the nerves involved in vision and eye movement are close to the pituitary gland.
Endocrinologists are medical specialists who deal with hormone problems, and therefore can help to sort out pituitary problems.
Why Tumours Cause Problems
Pituitary tumours can cause problems for several reasons.
- The tumour may secrete an excess amount of hormones, outside the usual control of the gland. However, tumours may also be nonfunctioning, and not secrete anything of clinical relevance.
- Tumours may press on the normal gland and prevent the normal hormonal secretion from the pituitary gland.
- Large tumours may cause problems with other structures in the same region as the pituitary gland. These include the optic chiasm (where the optic nerves from the back of the eye cross over on their way to the brain). Other nerves in the area include the nerves that control eye movement, and a pituitary tumour may cause pressure on these, causing double vision due to asynchronous eye movement.
- Occasionally, patients with pituitary tumours may bleed into their pituitary tumour, which can result in sudden headache, visual problems and hormone problems.
If a patient has a pituitary tumour, they may need medication, surgery and/or radiotherapy. This will depend upon several factors, including the size of the tumour, whether it is secreting a hormone in excess and whether it is causing damage to any other structures in the area, as well as the general health of the person affected.
If the tumour has resulted in a lack of normal hormone secretion by the pituitary gland, then these hormones will need replacing. Some forms of treatment for pituitary tumours (surgery and/or radiotherapy) can also affect the normal secretion by the pituitary gland, and hormone replacement may be needed in this circumstance also.
As mentioned above, some tumours make an excess production of hormones. Usually, only one excess hormone is secreted by pituitary tumours. However, many tumours do not appear to secrete any hormone of clinical relevance. These are called “non-functioning” tumours.
The commonest type of pituitary tumour (ie. one that secretes excessive amounts of hormone) is prolactinoma.
Autopsy studies have suggested that around 10% of the population have tiny microprolactinomas in their pituitary gland; these are usually silent and do not cause any clinical problems. However, around 10 in a million people will have clinical problems due to a prolactinoma each year (so around 200 people affected each year in Australia).
Normally, the pituitary gland secretes prolactin to help in the production of breast milk and lactation. If too much prolactin is secreted by a pituitary tumour, the breasts may swell (this is called gynaecomastia) and may even make milk (this is called galactorrhea). This can occur in people who are not breastfeeding, including men. Women with prolactinomas often notice their menstrual periods stopping. Men may notice that they have lost their libido (interest in sex) and may have impotence.
Prolactinomas are usually managed by medications that prevent both the excess secretion of prolactin and the growth of the tumour - in fact, usually these medications shrink the tumour. In some cases, patients with prolactinomas may need surgery.
Excess secretion of growth hormone causes a condition called acromegaly. This results in growth of those tissues able to grow. If there is excess growth hormone in children before their long bones fuse (usually in their mid to late teen years), they grow excessively tall – this is called gigantism. However, in adults whose bones have fused, excess growth hormone secretion can result in enlargement of the jaw, forehead, hands and feet. Bony overgrowth at joints can cause a particular type of arthritis. Patients may also have enlarged soft tissues, such as a big tongue, big nose, and very fleshy hands. The swollen tissues can cause patients to snore. Typically, patients have thick, greasy and sweaty skin and may have a lot of skin tags. Some patients have high blood pressure and even diabetes as a consequence of too much growth hormone. Acromegaly is not common – around 4 per million in the population per year, so around 80 people will be affected in Australia each year.
Patients with acromegaly have traditionally required surgery to remover the tumour; often, radiotherapy will be needed postoperatively also. There is also medicines that can control the excess growth hormone secretion. For some people, medicines may be the most appropriate first option, but most people will require surgery at some stage. Medications may also be necessary postoperatively if there is still excess growth hormone.
The success of surgical management in acromegaly depends in particular on the size and location of the tumour. Not surprisingly larger tumours can be much more difficult to remove completely. However, even in large tumours, debulking the tumour can have important clinical benefits even if the patient is not cured of acromegaly completely. The right course of management needs to be individualised for each patient, therefore.
Adrenocorticotrophic hormone (ACTH) is the hormone that controls secretion from the outer part (or cortex) of the adrenal gland. The most important hormone made by the adrenal cortex is cortisol. Excess cortisol causes a condition called Cushing’s syndrome, and when this is due to excess ACTH from the pituitary gland this is called Cushing’s disease.
Cushing’s syndrome results in many changes, including:
- excessive fat on the torso
- muscle wasting and weakness in the limbs (patients may find it difficult to climb stairs or to get out of a chair or up from squatting position)
- thin bones (osteoporosis)
- thin skin that bruises easily
- a reddened rounded face (sometimes called a moon face)
- facial hair (hirsutism) and thinning of head hair
- menstrual changes, infertility, and loss of libido
- high blood glucose
- mood disturbance including depression, euphoria, fatigue and difficulty sleeping.
Cushing’s syndrome is quite common in patients taking excess doses of steroid hormones for other health reasons (for example. to treat severe asthma or rheumatoid arthritis). However, Cushing’s disease itself is rare, with around 2 people per million in the population affected each year, so around 40 people affected in Australia annually.
Medication is sometimes used temporarily to get patients ready for theatre. Surgery is the usual means of managing Cushing’s Disease, although patients may often need further management over time such as radiotherapy or even a second operation. Rarely patients may need to have their adrenal glands removed to control the excess hormone secretion: almost always this would follow pituitary surgery and radiotherapy.
Thyroid Stimulating Hormone Tumours
Pituitary tumours secreting excess thyroid stimulating hormone (TSH) are even more rare than the above tumours. If this type of tumour is present, it causes an overactive thyroid. However, the vast majority of patients with an overactive thyroid do not have pituitary tumours secreting TSH! Endocrinologists are able to interpret thyroid function tests to determine if an overactive thyroid is due to this extremely rare cause.
Under the microscope, pituitary tumours often look as if they are secreting excess follicle stimulating hormone (FSH) and luteinising hormone (LH) but do not actually cause any symptoms or signs related to excess of these hormones. These tumours are often categorized as non-functioning tumours. Also, some pituitary tumours genuinely do not have any hormone secretion evident and the term non-functioning tumour is used for these also.
Are Pituitary Tumours Hereditary?
Sometimes pituitary tumours can run in families. This can occur as part of the Multiple Endocrine Neoplasia syndrome type 1, associated with excess parathyroid hormone production and with tumours in the pancreas. There are other forms of heritable tumours also; but these are thought uncommon overall.
Deficiency of Pituitary Hormones
Damage to the pituitary gland can result in a loss of its normal hormone production. This can occur because of severe head trauma, pressing of a tumour on the normal gland, bleeding(haemorrhage) into the pituitary gland, radiotherapy, surgery, or any other cause of damage. The gland may lose all its normal production of hormones (called panhypopituitarism) or only some of the normal hormone production (partial hypopituitarism). Occasionally, if a pituitary tumour has been pressing on the normal gland, recovery of normal pituitary function can occur after surgery.
Replacement of Pituitary Hormones
As described above, the pituitary gland controls the secretion of a number of hormones from other glands. If a person is deficient in their pituitary hormone production, it is most common to replace the target gland hormone production rather than the pituitary hormone itself.
Persons deficient in ACTH will not make sufficient cortisol from their adrenal glands. These people will need to take adequate cortisol replacement in the form of hydrocortisone, cortisone acetate, prednisolone or other corticosteroid hormone. In times of sickness, the dose of the replacement hormone will need increasing. Patients on corticosteroid hormone replacement need to carry a card in their wallet/purse or wear a MedicAlert bracelet or similar in case of an accident or emergency, when it will be essential for the caring emergency team to know that the patient will need corticosteroids.
Follicle Stimulating Hormone and Leutinising Hormone Deficiency
FSH and LH are important in women for normal menstrual cycling, which includes production of oestrogen and progestogen by the ovary, the regular release of eggs from the ovaries, and normal menstruation. In men, LH and FSH control testosterone and sperm production from the testes (or testicles). Deficiency of FSH and LH will result in lack of normal menstrual cycling and infertility in women, and in impotence and infertility in men.
Young women (less than 50) with FSH and LH deficiency are usually given replacement oestrogen and progestogen, either in the form of HRT or the oral contraceptive pill; this is particularly important to prevent osteoporosis. Replacement of these hormones in women of postmenopausal age (over 50 years) is no longer routine. Men with LH and FSH deficiency are usually treated with testosterone, which can be given in several different ways including injection, implantation, and a gel form. Patients with LH and FSH deficiency will need special help for fertility.
Thyroid Stimulating Hormone Deficiency
Patients deficient in TSH are given thyroxine. Endocrinologists use the thyroid function test to help guide appropriate dosing.
Growth Hormone Deficiency
Children with GH deficiency will not grow properly and replacement of GH is important to prevent them from being too short. Adults with GH deficiency have perturbations in their fat and muscle balance, such that they tend to have increased body fat and reduced muscle mass. They may also have mood disturbance. Replacement of GH in adults is controversial and is not currently available on the Pharmaceutical Benefits Scheme in Australia.
The posterior pituitary gland normally secretes a hormone called anti-diuretic hormone (also known as vasopressin) which causes the kidney to hold onto water. Lack of this hormone causes excess loss of water by the kidneys. This is known as diabetes insipidus. Patients may pass great quantities of urine and feel terribly thirsty. This hormone can be replaced both by tablets and by nasal spray.
Other Pituitary Problems:
A craniopharyngioma is a cyst-like tumour which occurs in the area of the pituitary gland. It is thought that these tumours arise because of the way the brain forms during early life. Craniopharyngiomas often cause loss of normal hormone production by the pituitary gland as well as compression on other structures in the area. Craniopharyngiomas are rare tumours, with around 1-2 per million in the population diagnosed each year. Craniopharyngiomas are sometimes diagnosed in childhood but may not become evident until adulthood. Surgery is usually required, as is radiotherapy. It is not uncommon for the tumour to reoccur.
Rathke’s Cleft Cyst
Rathke’s cleft cyst is a similar lesion to a craniopharyngioma. Surgery is not always required.
Both craniopharyngioma and Rathke's cysts are discussed elsewhere on this website.
Sheehan’s Syndrome refers to damage to the pituitary gland due to major blood loss (infarction of the pituitary gland), usually during delivery of a baby. It is often first diagnosed when the mother is unable to breast feed her baby because of loss of prolactin production by the pituitary gland. With modern obstetric care, it is unusual for women to have such large blood loss around the time of giving birth, and this syndrome therefore has become less common in the developed world.
As pituitary problems may be quite complex and may evolve with time, lifelong follow-up by a specialist endocrinologist is advisable, even after successful correction of the initial problem.
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This article updated: March 2013