Tests for Pituitary Tumors

Pituitary tumors are usually found when a person goes to the doctor because of symptoms they're having. But sometimes these tumors don’t cause symptoms, and they're found when a person has an imaging test of the head for some other health issue. (Tumors found this way are known as pituitary incidentalomas.)

If there’s a reason to suspect you might have a pituitary tumor, your doctor will do exams and tests to find out. Signs and symptoms might suggest that you could have a pituitary tumor, but tests are needed to be sure of the diagnosis and find out what kind of pituitary tumor it is.

Medical history and physical exam

If your symptoms lead your doctor to believe that you might have a pituitary tumor, the first step is to get your medical history to learn more about your symptoms and to check for possible risk factors. Your doctor may ask about your family history of tumors or other problems to see if you might have an inherited genetic syndrome, such as multiple endocrine neoplasia, type I (MEN1).

Your doctor will also examine you to look for possible signs of a pituitary tumor or other health problems. This will probably include exams to look for vision or nervous system problems that could be caused by a tumor.

If a pituitary tumor is strongly suspected, your doctor may refer you to an ophthalmologist (eye doctor) to check your vision more carefully, as pituitary tumors can damage nerves leading to the eyes. The most common test is to measure how well you can see. The doctor may also test your field of vision (or visual fields). Pituitary tumors can press on parts of the optic nerves (the nerves leading from the eyes to the brain). This can lead to the loss of peripheral vision, meaning that you can't see things off to the side without actually looking right at them. Eye doctors have special instruments that can test for this.

You might also be referred to other doctors, such as an endocrinologist (a doctor who treats diseases in glands that secrete hormones) or a neurosurgeon (a doctor who uses surgery to treat brain and pituitary tumors), who might order other tests.

Lab tests of hormone levels

If your doctor suspects you might have a hormone-producing pituitary tumor, hormone levels in your blood, urine, and/or other body fluids will be measured.

Somatotroph (growth hormone-secreting) adenoma

A physical exam may alert the doctor to look for this tumor because the signs and symptoms (of acromegaly or gigantism) are often very distinctive.

The first step is usually to check the level of insulin-like growth factor-1 (IGF-1) in your blood. When growth hormone (GH) levels are high, it causes the liver to make more IGF-1. Blood GH levels can be checked as well, but testing the IGF-1 level can often be more helpful because the IGF-1 level doesn’t change much during the day, while the GH level can.

If blood levels of IGF-1 (or both) are very high, the diagnosis is almost certainly a pituitary tumor.

If the levels are slightly increased, an oral glucose tolerance test is often done to be sure. You'll be asked to drink a sugary liquid, and then the levels of GH and blood sugar (glucose) will be measured at certain times. The normal response to suddenly taking in so much sugar is a drop in GH levels. But if the GH levels stay high, a pituitary tumor is likely the cause.

Corticotroph (corticotropin or ACTH-secreting) adenoma

Most of the signs and symptoms of ACTH-secreting tumors come from having too much cortisol (an adrenal steroid hormone) in the body. But there are also other reasons the body might have too much cortisol, such as if a person is taking some type of steroid or has an adrenal tumor. Having too much cortisol in the body leads to a condition called Cushing’s syndrome. If you have symptoms suggesting this syndrome, you'll need tests to see if it’s caused by a pituitary tumor (in which case it’s known as Cushing’s disease) or by something else.

Tests that might be done include:

• Late-night salivary cortisol: This test measures the levels of cortisol in your saliva late at night to see if they stay elevated. (They normally drop at night.)
• 24-hour urinary cortisol excretion: For this test, you collect all of your urine over a 24-hour period, which is then tested to measure your daily production of cortisol and other steroid hormones.
• Dexamethasone suppression test: This test involves taking a dose of a cortisone-like drug called dexamethasone, then having your blood or urine cortisol levels checked.
• Petrosal sinus sampling: This test is typically done in an operating room. Catheters (long, soft, small tubes) are put into veins on each inner thigh through tiny cuts and are guided up into the petrosal sinuses, which are small veins near the base of the brain that drain blood from each side of the pituitary. An injection of corticotropin-releasing hormone (CRH) is typically given, which causes the pituitary to make more ACTH. Blood samples are taken from the 2 catheters at different times before and after the injection, as well as from another part of the body. These samples are tested to see if the ACTH level is higher in the blood from the pituitary (and if so, if it is higher on one side than the other). If it is, the source of the high ACTH level is very likely a pituitary tumor.

Often more than one of these tests is needed to help distinguish ACTH-secreting pituitary tumors from other conditions that can cause similar symptoms, such as adrenal gland tumors.

Lactotroph (prolactin-secreting) adenoma (prolactinoma)

Blood prolactin levels can be measured to check for a prolactinoma. Blood levels of other hormones might also be checked, as other types of pituitary tumors (and other conditions) can also sometimes cause prolactin levels to rise.

Gonadotroph (gonadotropin-secreting) adenoma

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) blood levels can be checked to see if you have a gonadotropin-secreting tumor. Levels of related hormones, such as estrogen, progesterone, and testosterone, are often checked as well.

Thyrotroph (thyrotropin-secreting) adenoma

Tests to measure blood levels of thyrotropin (also known as thyroid-stimulating hormone, or TSH) and thyroid hormones can usually identify people with a thyrotropin-secreting adenoma.

Non-functional adenoma

Non-functional (non-functioning) pituitary adenomas don’t make enough excess hormones to cause symptoms. Sometimes, though, blood levels of pituitary hormones might still be higher than normal, even if they're not causing symptoms. They might also be lower than normal if the tumor has grown big enough to press on the pituitary cells that normally make these hormones. Because of this, checking blood hormone levels might still be helpful.

Testing for diabetes insipidus

Diabetes insipidus can develop if a pituitary tumor grows large enough to damage the part of the pituitary that stores the hormone vasopressin (also known as antidiuretic hormone, or ADH), which leads to too much water being lost in the urine. This condition can also have other causes, including surgery to treat pituitary tumors or other tumors near the pituitary gland.

In many cases, the cause of diabetes insipidus can be determined with tests that measure the amount of urine made over a 24-hour period, sodium and glucose levels in the blood, and osmolality (total salt concentration) of the blood and urine.

If these test results are not clear, then a water deprivation test may be done. In this test, you are not allowed to drink fluids for several hours, sometimes overnight. After the water restriction, your blood and urine osmolality and your blood sodium level will be checked. If your pituitary isn't making enough vasopressin, you'll continue to make urine even though you aren't taking in any fluid. This will cause your urine osmolality to remain low, as opposed to rising as it normally would if your urine was being concentrated. You may also be given an injection of vasopressin to see if this corrects the problem.

Imaging tests

Imaging tests use x-rays, magnetic fields, or other means to create pictures of the inside of your body. You might have one or more of these tests to look for pituitary tumors or to see if they have grown into nearby structures. In some cases, an imaging test of the head done for another reason may show a pituitary tumor.

Magnetic resonance imaging (MRI)

MRIs use radio waves and strong magnets to create detailed pictures of the inside of the body.

This test is very helpful for looking at the brain and spinal cord, and it's considered the best way to find pituitary tumors. MRI images are usually more detailed than those from CT scans (see below). They can show macroadenomas of the pituitary gland, as well as most microadenomas. MRI might not detect very small microadenomas, although many of these can now be seen with newer MRI machines, which have stronger magnets and can show even more detail.

Computed tomography (CT) scan

A CT scan uses x-rays to create detailed cross-sectional images of part of your body. CT scans can find a pituitary adenoma if it's large enough, but MRI scans are used much more often to look at the brain and pituitary gland.

Lab tests of pituitary tissue samples

In diagnosing cancers and tumors in most other parts of the body, imaging tests and blood tests may strongly suggest a certain type of tumor, but a biopsy (removing a sample of the tumor to examine under a microscope) is often the only way to be sure of the diagnosis. In many cases, doctors won't treat a tumor until a biopsy has been done.

A biopsy, however, isn't usually needed before treating a pituitary tumor. One reason is that the hormone tests for most types of pituitary adenomas are very accurate, so a biopsy isn’t likely to provide much more information. Biopsies in this part of the body can also pose a risk of serious side effects, even though this risk is small. Also, some types of adenomas can be treated without surgery, using medicines or radiation therapy.

When pituitary tumors are removed by surgery, they're looked at under a microscope to determine their exact type. Special stains may be used on the tumor to color the areas making hormones, and other lab tests may be done as well to help classify the tumor.