A pituitary adenoma is a benign tumour of the anterior pituitary gland. The pituitary is a pea-sized gland located at the base of the brain that normally produces hormones which control other glands in the body. The pituitary produces several different hormones.
- Prolactin, which is involved in breastfeeding
- Growth hormone, which helps control body growth and the utilisation of sugar and fats in the body
- Thyroid-stimulating hormone, which causes the thyroid gland to produce other hormones that regulates metabolism
- Adrenocorticotropic hormone (ACTH), which controls the production of cortisol, involved in the body’s response to stress
- Luteinizing hormone (LH) and follicle stimulating hormone (FSH) that control the menstrual cycle in women and sperm production in men.
Pituitary adenomas may be functioning, meaning they produce more than the usual amount of hormones, or non-functioning, meaning they do not make extra hormones.
Pituitary adenomas are also classified by size. Tumours smaller than 1cm are called microadenomas and tumours larger than 1cm are called macroadenomas.
What Are the Causes of Primary Brain Tumours?
Only a small percentage of pituitary adenomas are linked to a hereditary condition. Rare inherited conditions that can increase the risk of developing a pituitary adenoma include;
- Multiple endocrine neoplasia type 1 (MEN-1) syndrome
- Isolated familial acromegaly
What Are the Symptoms of Brain Tumours?
Symptoms caused by a pituitary adenoma are caused by the tumour pressing on nearby structures and/or by additional hormone production. In some patients a pituitary adenoma may be diagnosed incidentally when a CT or MRI scan of the head is done for other reasons. In these cases the pituitary adenoma may not be associated with symptoms.
Non-functioning adenomas may cause symptoms if they press on nearby structures causing headache or loss of vision. Loss of vision is caused by pressure on the nerves that are important for vision (optic chiasm). If visual loss occurs it is usually of gradual onset and involves reduced vision at the outer edges of the visual field. Non-functioning adenomas can also press on or damage parts of the pituitary gland, causing reduced hormone levels, which may cause;
- Loss of body hair
- Lack of sex drive
- For women, irregular or no menstrual periods
- For men, loss of facial hair, growth of breast tissue and/or erectile dysfunction
- For children, slowed growth and delayed puberty
Other less common symptoms include double vision and leakage of clear spinal fluid from the nose.
Functioning adenomas may cause symptoms resulting from additional hormone production. Symptoms depend on which hormone is being over-produced.
Too much prolactin can cause
- Less frequent, very light or no menstrual periods
- Erectile dysfunction in men
- Low sex drive
- Production of breast milk in women who are not pregnant or breastfeeding
Too much growth hormone can cause
- In adults, excessive growth of the bones in the face, hands and feet (acromegaly)
- In children, rapid growth and extra height
- Snoring or sleep apnoea
- Joint pain
- Excess sweating
Too much ACTH can cause
- Weight gain in the face, neck and trunk
- A fatty lump on the back of the neck (“buffalo hump”)
- Thin skin with stretch marks on the chest or abdomen
- Easy bruising
- Growth of fine hair over the face, arms or upper back
- Anxiety or depression
Too much thyroid-stimulating hormone can cause
- Irregular heartbeat
- Weight loss
- Difficulty sleeping
- Excessive sweating
- Tremor or shakiness
What Are the Treatments for Primary Brain Tumours?
Small pituitary adenomas that are picked up by chance and not causing symptoms may not need immediate treatment. In these cases the pituitary adenoma will be monitored with regular scans.
Larger pituitary adenomas and those causing symptoms usually need treatment. The type of treatment recommended depends on the type of adenoma (functioning or non-functioning) and its size. Possible treatment options include medication, surgery and/or radiation therapy.
Functioning pituitary adenomas (those producing excess hormones) may be treated with medications that stop the adenoma from producing hormones. The medication also controls the growth of the adenoma. The type of medication recommended is specific for the type of hormone being produced by the adenoma.
Surgery is usually recommended for functioning adenomas that are not responding to medical therapy, or if the adenoma is compressing adjacent structures.
If an adenoma is thought to be surgically resectable this may be done via a small cut made under the upper lip or at the back of the nose (transphenoidal surgery). If the adenoma is not accessible using this route, surgery may be performed via a cut through the skull (craniotomy). If there is residual adenoma left after surgery, post-operative radiation therapy may also be recommended.
Radiation therapy may be used after surgery if there is residual adenoma remaining or if the adenoma recurs following surgery. In some cases radiation therapy may be recommended as primary treatment if the pituitary adenoma is non-functioning and surgery can not be performed.
Radiation therapy may be given as stereotactic radiosurgery (SRS), which involves a single dose of highly focused radiation therapy, or as conventional fractionated radiation therapy, which involves small doses of radiation, 5 days a week usually for a period of 5-6 weeks. Stereotactic radiosurgery is usually used for small tumours (less than 3cm) that are a safe distance (3-5mm) away from sensitive structures such as the optic nerves and optic chiasm. Larger adenomas or those very close to the optic chiasm are treated with fractionation radiation therapy to reduce the risk of damaging the optic nerve pathways.
How effective is radiation therapy?
Radiation therapy, either SRS or fractionated radiation therapy is very effective in controlling adenoma growth. 90% of tumours will remain controlled at 5-10 years.For functioning adenomas, the goals of treatment are to both control growth and reduce hormone production to normal levels. Radiation therapy has been reported to control hormone levels in between 50-80% of cases, but it can take several years for hormone levels to normalise.
What Are the Side Effects of Radiation Therapy?
Possible short-term side effects that can occur during or just after a course of radiation therapy include fatigue, headache, nausea and/or vomiting, skin redness and patchy hair loss. These side effects generally resolve within 1-2 weeks of finishing treatment.
Possible late side effects that can occur months to years after treatment include:
Hypopituitarism (reduced production of normal pituitary hormones) can occur in approximately 20-30% of patients, usually within 5-10 years after treatment. This risk increases slowly with time so long term monitoring of hormone levels following treatment is usually advised.
- Rarely radiation therapy can cause injury to the optic nerves or optic chiasm which can result in visual loss. This risk is higher if the tumour lies very close to the optic pathway or if stereotactic radiosurgery is used. For fractionated radiation therapy the risk of damage to the optic pathway is less than 1% at 10 years. The risk is minimised by ensuring the radiation dose to these structures is kept to a low level.
- There is potentially a small increased risk of stroke following treatment. However it is difficult to distinguish the risk from radiation from other pre-existing cardiovascular risk factors.
- Second cancers occurring as a result of radiation therapy are an uncommon side effect.
The best person to discuss radiation therapy for bladder cancer is a radiation oncologist. You can ask your Surgeon or General Practitioner for a referral to a Radiation Oncologist for a discussion about whether radiation therapy is a suitable treatment option for you.
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