Your symptoms and physical exam results may lead your doctor to believe that you might have a pituitary tumor. If your doctor suspects you have a hormone-producing tumor, the next step is to measure hormone levels in blood and/or urine samples.

Biochemical testing for growth hormone-secreting adenomas: A physical exam may alert the doctor to look for these tumors because the signs and symptoms are often very distinctive . The next step is to check for excessive growth hormone production. Levels of growth hormone and insulin-like growth factor-I (IGF-I) will be measured in your blood samples, which are taken the morning after an overnight fast. Experts think that the IGF-1 test is the most important one because growth hormone levels tend to vary during the day.

If both levels are very high, the diagnosis is clearly a pituitary tumor. If the levels are slightly increased, a glucose suppression test is done. You will be asked to drink a sugary liquid, and your growth hormone levels 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.

Biochemical testing for corticotropin (ACTH)-secreting adenomas: Quite a few diseases can cause overproduction of adrenal steroid hormones. Patients with symptoms suggesting this condition need tests to determine whether a pituitary tumor is the cause.

These tests may include measuring levels of cortisol and ACTH in blood samples taken at different times of the day. A sample of all the urine a person produces over a 24-hour period is often tested to measure daily production of cortisol and other steroid hormones. Other tests include measuring ACTH levels. These may be repeated after taking a dose of a powerful, cortisone-like drug called dexamethasone. These tests help to distinguish patients with corticotropin-secreting adenomas from patients with other diseases, such as adrenal gland tumors, that may cause similar symptoms.
 

Biochemical testing for prolactin-secreting adenomas (prolactinomas), gonadotropin-secreting adenomas, and thyrotropin-secreting adenomas: Prolactinomas are always associated with high blood prolactin levels. Likewise, patients with gonadotropin-secreting tumors have high luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in their blood. Tests to measure blood levels of thyrotropin (TSH) and thyroid hormones can usually identify people with a thyrotropin-secreting adenoma.

Biochemical testing for nonfunctional (null cell) adenomas: A pituitary adenoma is considered nonfunctional if tests for excessive hormone production are negative. Some pituitary hormone blood levels may actually be lowered because the adenoma interferes with their production.

Biochemical testing for diabetes insipidus: Diabetes insipidus is caused by damage to the part of the pituitary that produces vasopressin. This condition can be caused by macroadenomas of several types and by pituitary carcinomas, but it is more common with metastatic cancer. It sometimes occurs as a side effect of surgical treatment of pituitary tumors.

In many cases, this diagnosis is made by tests to measure sodium (salt) 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 necessary. This is a test to determine whether your kidneys retain body water when you are not allowed to drink fluids for several hours. The test is often done overnight. If there is not enough vasopressin produced, you will continue to urinate even when you do not drink anything. You may also be given an injection of vasopressin to see if this corrects the problem.

Venous Blood Sampling

Corticotropin-secreting adenomas are often too small to be detected by MRI scans. When biochemical test results indicate a corticotropin-secreting adenoma, but the patient�s MRI scan is normal, then a venous sampling study may be useful.

In this study, catheters (small tubes) are placed into the groin veins through a small nick in the skin and guided into the petrosal sinuses, which hold 2 small veins that drain the blood from each side of the pituitary gland. After an injection of corticotropin-releasing hormone (CRH), blood samples are taken from both sides and compared to see if the ACTH level is higher on one side than the other. The side with the higher ACTH level contains the pituitary tumor.

Imaging Tests

Computed tomography (CT): The CT scan is an x-ray procedure that produces detailed cross-sectional images of your body. Instead of taking one picture, like a conventional x-ray, a CT scanner takes many pictures as it rotates around you. A computer then combines these pictures into an image of a slice of your body. The machine will take pictures of multiple slices of the part of your body that is being studied. Often after the first set of pictures is taken you will receive an intravenous (IV) injection of a radiocontrast agent, or �dye,� that helps better outline structures in your body. A second set of pictures is then taken.

CT scans take longer than regular x-rays and you will need to lie still on a table while they are being done. But just like other computerized devices, they are getting faster and your stay might be pleasantly short. The newest CT scans take only seconds to complete. Also, you might feel a bit confined by the ring-like equipment you�re in when the pictures are being taken.

The contrast dye is injected through an IV line. Some people are allergic to the dye and get hives, a flushed feeling, or rarely more serious reactions like trouble breathing and low blood pressure can occur. Be sure to tell your doctor if you have ever had a reaction to any contrast material used for x-rays. If you have, you may need medicine before you can have such an injection during your test.

The CT scan can find a pituitary adenoma if it is large enough. It is used less often than the MRI (see below), which is better at finding adenomas.

Magnetic resonance imaging (MRI): MRI scans use radio waves and strong magnets instead of x-rays. 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 of radio waves given off by the tissues into a very detailed image of parts of the body. A contrast material might be injected to improve the quality of the image.

MRI scans are particularly helpful in examining the brain and spinal cord. MRI scans can be uncomfortable. First, they take a long time - often up to an hour. Also, you have to lie inside a tube, which is confining and can upset people with claustrophobia (a fear of enclosed spaces). The machine also makes a thumping noise, but some places provide headphones with music to block this out. You will also be given an injection of a contrast agent called gadolinium, which will help outline a pituitary adenoma.

MRI is the best imaging test to identify pituitary tumors of all types. MRI can identify a macroadenoma of the pituitary gland, as well as most microadenomas. But the MRI may not be able to detect microadenomas that are smaller than 3 mm (about 1/8 inch). 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.

Testing of Vision and Visual Fields

Because the tumor can damage nerves leading to the eyes, vision should be tested. The most common test is to test how well a person can see. A more subtle test is to test visual fields. The tumors will only damage part of the optic nerves at first. This means that only part of a person�s vision will be lost. This is usually the �peripheral vision,� meaning things that you can see on one side or the other without actually looking directly at them. Eye doctors have special instruments that can test for this.

Examination of Pituitary Tissue Specimens

In diagnosing tumors of most parts of the body, imaging tests and blood tests may strongly suggest a particular type of tumor. However, a biopsy (taking a sample of the tumor to examine under the microscope) is considered the only way to be certain of that diagnosis.

In many situations, doctors will not treat a tumor until a biopsy has been done. A pituitary tumor is one of the exceptions to this general rule. One reason is that biochemical tests for some types of adenomas are very accurate. The other reason is that 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. Immunohistochemical studies are often done. These studies use special antibodies made the laboratory. They are attached to chemicals giving color to the areas of hormone production, which allows specific pituitary hormones to be seen.