Tumours of the pituitary gland (known as pituitary adenomas) are actually pretty common; they make up about 13% of all diagnosed brain tumours, and as this study shows, a surprising number of people in the general population may have a pituitary adenoma without realising it. Often they don't cause any symptoms at all, with many adenomas only discovered on autopsy or when someone has an MRI for an unrelated reason. If you're ever accosted by your own brain cells, who tell you that they've decided to go neoplastic but they'll give you the choice of what kind of tumour to have (unlikely, but you never know), pick a pituitary adenoma.
However, they can be troublesome things too. Even though most pituitary adenomas are benign (i.e. not cancerous), they are sited close to important brain structures, blood vessels and the optic nerve, and they can cause headaches, loss of sight, and play havoc with the endocrine system. Around 75% of these tumours are secretory, meaning that they actively produce one or more pituitary hormones; the other 25% of tumours often result in the under-production of hormones by the pituitary gland.
The different kinds of secretory pituitary adenoma are as follows:
Prolactinoma - the most common kind of pituitary adenoma, these tumours secrete the hormone prolactin (often abbreviated to PRL). Symptoms can include galactorrhea (inappropriate secretion of breast milk), infertility and amenorrhea (absence of periods) in women; and erectile dysfunction and gynecomastia (man boobs!) in men. Usually treated with the drug bromocriptine, or with surgery/radiotherapy if this is unsucessful.
Corticotrophic adenoma - these pituitary adenomas are quite rare (although like pituitary tumours generally, they may be underdiagnosed) and secrete adrenocorticotrophic hormone (ACTH), leading to a condition called Cushing's Disease, the symptoms of which include rapid weight gain, excessive sweating, impotence, infertility, insomnia, hair loss, high blood pressure, diabetes, and psychological disturbances. Usually treated with surgery/radiotherapy.
Gonadotrophic adenoma - these pituitary tumours may secrete either or both luteinising hormone (LH) and follicle-stimulating hormone (FSH). They are often not detected until they become large enough to cause headaches or affect sight, as they tend to secrete hormones erratically and do not usually cause a recognisable syndrome. Gonadotophic adenomas are treated with surgery/radiotherapy.
Somatotrophic adenoma - these are very rare pituitary adenomas (with a prevalence of around 40-60 cases in a population of a million) which secrete growth hormone (GH), causing a condition known as acromegaly. Symptoms include swelling of soft tissue resulting in enlargement of hands, feet, nose, lips and ears. Internal organs may also swell, the brow and jaw may protrude, and the tongue grow in size. Even more rarely, if the illness begins in childhood it may cause pituitary gigantism, with sufferers growing to heights of seven or eight feet. These tumours can be treated with surgery, radiotherapy or drugs including dopamine agonists such as bromocriptine, somatostatin analogues such as lanreotide, or a newer treatment called pegvisomamt.
Thyrotropic adenoma a.k.a. TSHoma (or thyrotropinoma) - these pituitary tumours secrete thyroid-stimulating hormone (TSH) and are the rarest kind of pituitary adenoma, with a prevalence of one in a million; only about 400 cases have been published. This is the kind of pituitary tumour I have! Because I just like to be unusual. Symptoms are basically similar to hyperthyroidism and include racing heart, palpitations, tremor, hair loss, weight loss (didn't get that one, sadly), increased appetite and hyperactivity. Treatment is usually surgery/radiotherapy and/or somatostatin analogues such as lanreotide.
It's clear therefore that, given the many different hormones that can be produced by pituitary adenomas, the symptoms and treatments employed can vary significantly between different types of tumour. Equally, if the pituitary tumour suppresses rather than increases the production of hormones, this can be extremely dangerous - a life-threatening Addisonian crisis can be caused if the body does not produce enough ACTH.
Diagnosis of pituitary adenomas is usually through epic amounts of blood tests (and urine tests in the case of Cushing's Disease) and then MRI scanning (or CT scanning if MRI is contraindicated), which will usually give a picture of the adenoma itself. These tumours are classed as either microadenomas, when they are less than 10mm in size, or macroadenomas, when they are larger than 10mm.
But why not do the MRI scan first rather than stealing pints of blood from the patient first, I hear you cry? Because pituitary adenomas have such a high prevalence in the general population, endocrinologists want to be confident that the adenoma on the scan is actually what's causing the symptoms. It would be terrible to tell a patient that they have a diagnosis, put them through surgery, and then discover that in fact the tumour on their pituitary gland was not the cause of their illness, but was simply an incidental finding and as such could have been left alone.