Tests for Pituitary Tumors

A physical exam might alert the doctor to look for a somatotroph adenoma 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 the IGF-1 level is often more helpful because it doesn’t change much during the day, while the GH level can.

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

If IGF-1 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.

Most of the signs and symptoms of ACTH-secreting pituitary tumors come from having too much cortisol (a steroid hormone made by the adrenal glands) 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 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 disease, or if the cause is something else.

Several tests might be done.

Late-night (bedtime) salivary cortisol: Cortisol levels normally drop at night. This test measures the levels of cortisol in your saliva late at night to see if they stay elevated.

24-hour urinary free cortisol (UFC) excretion: For this test, you collect all 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 (DST): This test involves taking a cortisone-like drug called dexamethasone, then having your blood or urine cortisol levels checked. There are different versions of this test, using different doses and different periods of time.

Inferior petrosal sinus sampling (IPSS): This test might be used if an MRI of the head doesn’t clearly show a pituitary tumor. It is typically done in an operating room. Catheters (long, soft, small tubes) are put into veins on each inner thigh and are guided up into the petrosal sinuses, which are small veins near the pituitary. An injection that causes the pituitary to make more ACTH is typically given. Blood samples are taken from the catheters before and after the injection. 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.

Blood (serum) 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 cause prolactin levels to rise.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) blood levels can be checked to see if you have a gonadotropin-secreting tumor.

Levels of other hormones, such as prolactin, estrogen, progesterone, and testosterone, are often checked as well.

Tests to measure blood levels of thyrotropin (also known as thyroid-stimulating hormone, or TSH) and thyroid hormones such as T4 can usually identify people with a thyrotropin-secreting 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.

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 the best way to find pituitary tumors.

MRI images are usually more detailed than those from CT scans. They can show macroadenomas (larger tumors) of the pituitary gland, as well as most microadenomas (smaller tumors). MRI might not detect very small microadenomas, although many of these can now be seen with newer MRI machines, which can show even more detail.

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.

For a PET scan, you are injected with a slightly radioactive substance that collects mainly in tumor cells. A special camera is then used to create a picture of areas of radioactivity in the body. The pictures aren’t as detailed as those from an MRI, but they can sometimes help spot a tumor that isn’t visible on MRI.

PET/CT scan: Many centers now use machines that can do both a PET scan and a more detailed CT scan at the same time.