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The most important diseases of the pituitary are probably the pituitary adenomas.
This is for the purposes of education only.
What are Pituitary Tumors?
Pituitary tumors which are usually benign are called pituitary adenomas and represent the bulk of pituitary disease in general.
They’re broken down into microadenomas and macroadenomas. Micro is less than a centimeter, macro is greater than a centimeter. So that’s easy enough.
I said benign above because they are generally well differentiated tumors. One of the general concepts you will find in medicine is that when a growth or tumor is well differentiated, it doesn’t tend to spread. This is the case for pituitary adenomas. They are however malignant in the sense they are dangerous because of their position – in the brain.
So, they have a space occupying or mass effect. And I touched on this in the other topic on pituitary diseases in general in that superior growth of the tumor hits the optic chiasm, affecting visual fields, lateral growth effects sinus cavities producing sinus symptoms and rhinorrhea of cerebrospinal fluid, dural encroachment produces headaches, cranial nerve irritation produces motor deficits called palsies, and so forth.
In addition to the mass effects of pituitary adenoma growth, the patient will display endocrine problems consistent with the hormones they are hyper secreting.
The most common type of pituitary adenoma is the prolactin secreting adenoma. The excessive prolactin produces a drop in libido in men and excessive lactating and amenorrhea in women. Because dopamine inhibits prolactin secreting cells, dopamine agonist are used to treat prolactin secreting adenomas. As such, these patients don’t need surgery as much as the other pituitary adenoma patients, and their prognosis is generally better.
How is a Pituitary Adenoma Diagnosed?
Diagnosing these tumors is fairly straightforward. Prolactin secreting adenomas yield high prolactin levels in the blood. But many other conditions also cause high prolactin levels. So, the work up must rule out kidney disease (the kidneys clear prolactin so if there’s kidney disease, prolactin levels will be high), thyroid disease (Thyroid Releasing Factor, TRF secreted by the hypothalamus, also stimulates prolactin production, so if there’s a hyperthyroid state because of high TRF, prolactin may be high), and other situations yielding high serum prolactin levels.
So that’s enough for prolactin secreting adenomas. Let’s turn to a few other types of pituitary adenomas.
What is Cushing’s Disease?
ACTH secreting pituitary adenomas produce a condition known as Cushing’s disease. The increased ACTH goes to the adrenals and leads to excessive steroid secretion there. The excessive adrenal steroids produce obesity, fatigue, and a myriad of other very unfortunate signs and symptoms. Cushing’s disease should be contrasted to Cushing syndrome.
Cushing’s disease is when there is a hypersecretion of ACTH by a pituitary adenoma. Cushing syndrome is when there is simply a surplus of corticosteroids in the body – either something else is making the adrenals do this; or the patient may be getting excessive steroids as a prescription. So, the excess of steroids is the syndrome, the excess of ACTH coming from a tumor in your pituitary driving up adrenal production of steroids is the disease.
And it’s important to make this distinction clinically so you know exactly how to treat the patient. A lot of testing in the urine and blood shows confusing similarities between the two disorders. So, the favorite diagnostic test used to distinguish Cushing’s disease from Cushing syndrome is called the dexamethasone suppression test.
Another recurring theme in medicine in general, if there is a disease process, you will want to document that you can suppress it to prove that it is a disease process and not just a normal low or a normal high. The dexamethasone suppression test is a great example of this. If you give a patient dexamethasone, a low dose should suppress the adrenal’s production of steroids if there is no pituitary tumor. If the pituitary requires a high amount of the steroid dexamethasone to suppress ACTH production, that implies Cushing’s disease, there’s an ACTH producing tumor of the pituitary we were talking about above. If it is impossible to suppress ACTH production of corticosteroids even using a high dose of dexamethasone, then it is more than likely that there is an ectopic source of ACTH production some in the body outside of the pituitary. Such an ectopic source will not respond to any corticosteroid feedback mechanisms as will a pituitary adenoma. So that’s three situations and how we make the distinction between them using the dexamethasone suppression test.
So that’s prolactin secreting adenomas. And that’s ACTH secreting pituitary adenomas. Here’s a few more types:
- Thyroid Stimulating Hormone (TSH) secreting
- Growth Hormone (GH) secreting
- Nonsecreting tumors
A patient with a pituitary adenoma may demonstrate either mass effects from the space occupying lesion in the brain or endocrine effects if there is a secretory nature to the pituitary tumor or both.
Treatment for these unfortunate patients ranges from surgical sphenoidectomy to remove the tumor, to somatomedin agaonists aimed at suppressing hormone production, to radiation of the pituitary which is unfortunately extremely slow plus can cause a great deal of fibrosis.