How Are Pituitary Tumors Diagnosed?
Pituitary tumors are usually found when a person goes to the doctor because of symptoms they are having. But sometimes these tumors don’t cause symptoms, and they are found by medical tests done for other health problems.
If there’s a reason to suspect you might have a pituitary tumor, your doctor will use one or more tests to find out. Signs and symptoms might suggest that you could have a pituitary tumor, but tests are needed to confirm the diagnosis.
Medical history and physical exam
If your symptoms lead your doctor to believe that you might have a pituitary tumor, the first step is take a complete medical history to check for risk factors and to learn more about your symptoms. 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 may 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 eye doctor to check your vision, 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). At first, pituitary tumors only press on part of the optic nerves. This often leads to the loss of peripheral vision, meaning things that you can see off to the side without actually looking directly 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.
Blood and urine tests of hormone levels
If your doctor suspects you might have a hormone-producing pituitary tumor, hormone levels in your blood and/or urine will be measured.
Growth hormone-secreting adenoma
A physical exam may alert the doctor to look for this tumor because the signs and symptoms are often very distinctive.
The next step is to check the levels of growth hormone and insulin-like growth factor-1 (IGF-1) in your blood samples, which are taken the morning after an overnight fast. When growth hormone levels are high, they cause the liver to make more IGF-1. Testing the IGF-1 level can be more helpful than checking the level of growth hormone, because the IGF-1 level doesn’t change much during the day, while the level of growth hormone can go up and down.
If both levels are very high, the diagnosis is clearly a pituitary tumor. If the levels are slightly increased, another test called a glucose suppression test is often done to be sure. You will be asked to drink a sugary liquid, and the levels of growth hormone and blood sugar will be measured at intervals afterward. The normal response to suddenly taking in so much sugar is a drop in growth hormone levels. If the growth hormone levels remain high, a pituitary adenoma is probably the cause.
Corticotropin (ACTH)-secreting adenoma
Most of the signs and symptoms of ACTH-secreting tumors come from having too much cortisol (an adrenal steroid hormone). Quite a few diseases can cause Cushing’s syndrome, in which the body makes too much cortisol. If you have symptoms suggesting this condition, you will need tests to determine if it’s caused by a pituitary tumor or something else.
These tests may include measuring levels of cortisol and ACTH in blood samples taken at different times of the day. You may be asked to collect all of your urine over a 24-hour period, which is then tested to measure daily production of cortisol and other steroid hormones. Blood or urine cortisol levels may be checked again after taking a dose of a powerful, cortisone-like drug called dexamethasone. Levels of cortisol in the saliva late at night can also be checked. These tests help to distinguish ACTH-secreting pituitary tumors from other diseases, such as adrenal gland tumors, that can cause similar symptoms.
Prolactin-secreting adenoma (prolactinoma)
Blood prolactin levels can be measured to check for a prolactinoma.
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.
Tests to measure blood levels of thyrotropin (TSH) and thyroid hormones can usually identify people with a thyrotropin-secreting adenoma.
Non-functional (null cell) adenoma
A pituitary adenoma is considered non-functional if it doesn’t make too much of a pituitary hormone. Pituitary hormone levels are not high in people with non-functional tumors. Sometimes, though, blood levels of some pituitary hormones may actually be low because the adenoma crowds out the cells that normally make these hormones.
Testing for diabetes insipidus
Diabetes insipidus can occur if the part of the pituitary that stores the hormone vasopressin (ADH) is damaged, which leads to too much water being lost in the urine. This condition can be caused by pituitary macroadenomas (or carcinomas in rare cases), or by tumors starting in parts of the brain or nerves next to the pituitary gland. It can also be a side effect of surgery to treat pituitary tumors or tumors next to the pituitary gland.
In many cases, this diagnosis is made 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 tests are inconclusive, then a water deprivation study may be done. In this test, you are not allowed to drink fluids for several hours. The test is often done overnight. If your body is not making enough vasopressin, you will continue to make urine even though you are not taking in any fluid. You may also be given an injection of vasopressin to see if this corrects the problem.
Venous blood sampling
Corticotropin (ACTH)-secreting adenomas may be too small to be seen on imaging tests such as MRI scans (see the next section). When the ACTH level is high, but a person’s MRI scan is normal, a venous sampling test may be useful to find the tumor.
For this test, catheters (small tubes) are placed into veins on each inner thigh through small nicks in the skin and are guided all the way up into the petrosal sinuses near the base of the brain. The sinuses hold 2 small veins that drain the blood from each side of the pituitary gland. After an injection of corticotropin-releasing hormone (CRH, a hormone from the hypothalamus that normally causes the pituitary to secrete ACTH), blood samples are taken from both sides and compared to see if the ACTH level is higher on one side than the other. If it is, the source of the high ACTH level is a pituitary tumor.
Imaging tests use x-rays, magnetic fields, or other means to create pictures of the inside of your body. They may be done 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 detect a pituitary tumor.
Magnetic resonance imaging (MRI) scan
MRI scans use radio waves and strong magnets to create detailed pictures of the inside of the body. The energy from the radio waves is absorbed and then released in a pattern formed by the type of tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body. A contrast material called gadolinium is sometimes injected into a vein to improve the quality of the image.
MRI scans are very helpful in looking at the brain and spinal cord and are considered to be the best way to identify pituitary tumors of all types. 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. But MRI might not detect microadenomas that are smaller than 3 mm (about 1/8 inch) across. Sometimes the MRI scan will show a small abnormality in the pituitary that has nothing to do with the patient’s symptoms. Between 5% and 25% of healthy people have some minor abnormality of the pituitary gland that shows up on an MRI scan.
MRI scans can take a long time – often up to an hour. You have to lie inside a narrow tube, sometimes with a small frame around your head, which can be confining and may upset people with a fear of enclosed spaces. Newer, open MRI machines may help with this, but the images might not be as detailed, so they can’t be used in all cases. The MRI machine also makes buzzing and clicking noises that may be disturbing. Some people may need medicine to help them relax for the test.
Computed tomography (CT) scan
The 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 is large enough, but MRI scans are used much more often to look at the brain and pituitary gland.
A CT scanner has been described as a large donut, with a narrow table that slides in and out of the middle opening. You will need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken. Instead of taking one picture, like a standard x-ray, a CT scanner takes many pictures as the camera rotates around you. A computer then combines these pictures into an image of a slice of your body.
Before the test, you may get an injection of a contrast dye through an IV (intravenous) line. This helps better outline any tumors that are present. The injection can cause some flushing (redness and warm feeling). A few people are allergic to the dye and get hives or, rarely, have more serious reactions like trouble breathing and low blood pressure. Be sure to tell the doctor if you have any allergies or have ever had a reaction to any contrast material used for x-rays.
Tests of pituitary tissue samples
In diagnosing tumors of most parts of the body, imaging tests and blood tests may strongly suggest a particular type of tumor, but a biopsy (removing a sample of the tumor to examine under a microscope) is usually the only way to be certain of the diagnosis. In many situations, doctors will not treat the tumor until a biopsy has been done.
But a biopsy is not usually needed before treating a pituitary tumor. One reason is that the hormone tests for some types of 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 very small risk of serious side effects. On top of this, some types of adenomas can be treated without surgery, using medicines or radiation therapy.
When pituitary tumors are removed by surgery, they are examined under a microscope to determine their exact type. Special stains may be used on the tumor to color the areas making hormones, which helps classify the tumor.
Last Medical Review: May 8, 2014 Last Revised: December 17, 2014