MRIs are an effective diagnostic tool for pituitary tumors. Although MRI scans can miss very small tumors, newer machines are better equipped to detect them.

Most pituitary tumors are noncancerous, or benign, tumors called pituitary adenomas.

A head MRI creates images of the brain and its various structures. Doctors may order this type of imaging test to help diagnose pituitary tumors.

Pituitary tumors can be functional and secrete hormones or non-functional, which means they do not secrete hormones. As part of the diagnostic work-up for pituitary tumors, a doctor may order tests to check hormone levels in the blood and urine.

This article describes how doctors use MRIs to diagnose pituitary tumors and discusses the accuracy of MRIs in detecting these tumors.

It also considers the next steps following a negative MRI result, outlines some additional diagnostic tests doctors may use, and answers some frequently asked questions about pituitary tumors.

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According to the American Cancer Society (ACS), MRI is the most effective method of detecting pituitary tumors, as it can provide more detailed images than other imaging forms.

However, an MRI can miss very small microadenomas. Newer MRI machines have stronger magnets and are better equipped to detect these very small tumors.

A 2021 study notes that contrast MRI is more effective at detecting pituitary microadenomas than non-contrast MRI. A contrast MRI involves injecting a dye into the circulatory system before the MRI to help enhance certain tissues and blood vessels on MRI scans.

Learn whether a pituitary tumor is a brain tumor.

MRIs and Cushing’s disease

A 2022 study notes that doctors often use MRI to help diagnose Cushing’s Disease. This condition can occur when a benign pituitary tumor triggers the release of excess cortisol into the blood.

Doctors refer to such tumors as adrenocorticotropic hormone (ACTH)-producing microadenomas.

However, according to the study, up to 64% of ACTH-producing microadenomas are undetectable on MRI.

Learn more about Cushing’s syndrome.

MRI accuracy and age

A 2022 study investigated the accuracy with which doctors interpret MRI scans of brain tumors in children.

Overall, the accuracy of reports was good, with 72.55% of 550 scans reaching the correct prediction. However, accuracy varied considerably according to tumor type and location.

Pituitary tumors were among the tumor types with the highest diagnostic accuracy, with pituitary adenomas having an accuracy of around 99.64%.

The study authors noted that this is likely due to pituitary tumors having characteristic and well-recognized radiological features and occurring in locations with limited potential for an alternative diagnosis.

Learn more about head and brain MRI scans.

A negative MRI result does not confirm the absence of a pituitary tumor since up to 64% of ACTH-producing pituitary microadenomas are undetectable on MRI.

In the case of suspected Cushing’s disease, people who continue to show signs and symptoms of the disease may benefit from a procedure called endoscopic endonasal transsphenoidal surgery (EETS).

In EETS, a surgeon inserts a flexible scope into the nostril and up into a small space in the nasal cavity called the sphenoethmoid recess.

The surgeon then opens up the area to access the pituitary gland. They may then take samples of the tumor and later analyze them under a microscope to determine the tumor type.

However, as the ACS explains, a person beginning treatment for a pituitary tumor does not usually require a biopsy. This is because hormone tests for most types of pituitary tumors are highly accurate, meaning there is little need for more biopsy samples.

Additionally, some of these tumors are treatable without surgery, using medications and radiation therapy.

Learn more about radiation therapy.

How urgent is a pituitary tumor?

According to Cancer Research UK, most pituitary tumors are slow-growing and benign. A person with a non-functioning tumor may only become aware of its existence following scans or tests for other conditions.

Even after diagnosis, an asymptomatic pituitary tumor may not require treatment. Instead, doctors may recommend a watch-and-wait approach.

However, people who have a genetic syndrome that increases their risk of a pituitary tumor may receive regular tests to help detect and treat these tumors early. This increases the likelihood of a cure.

In some cases, tumor can cause a blood clot or hemorrhage in the pituitary gland. Medical professionals refer to this as pituitary apoplexy. As a 2023 review explains, the condition can be life threatening without urgent medical treatment.

Anyone who has received a diagnosis of a pituitary tumor should seek urgent medical care if they experience potential symptoms of pituitary apoplexy, such as:

  • headache
  • nausea
  • vomiting
  • problems with vision

Learn more about the symptoms of a pituitary tumor.

The ACS lists some diagnostic tests that doctors may use to diagnose pituitary tumors. These include.

Hormone tests

Doctors may order hormone tests to help diagnose a hormone-producing pituitary tumor. These tests measure levels of certain hormones in the person’s blood, urine, or other body fluids.

The table below shows the types of tumor a doctor may test for, the types of tests they will order, and the hormones these tests measure.

Tumor typeTest typesHormones measured
Somatotroph (growth hormone-secreting) adenomaBlood• insulin-like growth factor-1 (IGF-1)
• growth hormone
• glucose
Corticotroph (corticotropin or ACTH-secreting) adenomaBlood and urinecortisol
Lactotroph (prolactin-secreting) adenoma (prolactinoma)Bloodprolactin
Gonadotroph (gonadotropin-secreting) adenomaBlood• luteinizing hormone (LH)
• follicle-stimulating hormone (FSH)
• estrogen
• progesterone
• testosterone
Thyrotroph (thyrotropin-secreting) adenomaBlood• thyrotropin or “thyroid-stimulating hormone” (TSH)
• other thyroid hormones

However, non-functioning pituitary tumors do not make enough excess hormones to cause symptoms but may make enough for a blood test to detect.

A large non-functioning tumor may also press on the pituitary gland, interfering with its hormone production ability. This could lead to lower-than-normal hormone levels on blood tests.

Learn more about blood tests for pituitary tumors.

Tests for diabetes insipidus

In some cases, a pituitary tumor can grow so large that it damages the part of the pituitary gland that makes the antidiuretic hormone called vasopressin. This causes a condition called diabetes insipidus, in which a person excretes too much water in their urine.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that in diabetes insipidus, blood glucose levels are normal, but the kidneys cannot properly concentrate urine.

Tests for diabetes insipidus include:

  • testing the amount of urine a person produces within 24 hours
  • testing sodium and glucose levels in the blood
  • testing salt concentration levels in the blood and urine

Learn how diabetes insipidus influences sodium levels.

Computerized tomography (CT) scan

A CT scan uses X-rays to create cross-sectional images of the body. These scans may detect large tumors, but MRI scans are better equipped to detect pituitary tumors.

Learn the difference between a CT and an MRI.

What is the most reliable test for pituitary function?

While MRI scans can detect pituitary tumors, hormone tests are the most reliable tests for pituitary function. These tests measure levels of certain hormones in the blood or urine and can help doctors diagnose hormone-producing pituitary tumors.

Can a pituitary tumor go undetected?

Not all pituitary tumors cause symptoms. For example, non-functioning ones may not cause symptoms unless they become very large and press on the pituitary gland and other nearby structures.

A pituitary tumor that does not cause symptoms may remain undetected unless a doctor discovers it during tests for another condition.

MRIs are the most effective method for detecting pituitary tumors. However, a negative MRI result does not necessarily mean that a person does not have a pituitary tumor.

When diagnosing pituitary tumors, doctors may order additional tests, such as blood and urine tests to check hormone levels. This is because certain types of tumor can secrete hormones, causing excess hormone levels in body fluids.

Similarly, a large pituitary tumor can press on the part of the pituitary gland that secretes hormones, resulting in lower-than-normal hormone levels.

Most pituitary tumors are benign, and a person may only discover their existence following tests for another health condition. Moreover, benign tumors do not always require treatment.

However, a person should contact a doctor if they suspect they may have a pituitary tumor or have received a diagnosis of one and develop new or worsening symptoms. The latter may indicate a medical emergency called pituitary apoplexy, which requires urgent treatment.