Pituitary Microadenoma on MRI: What Does It Mean and What Happens Next?

A pituitary microadenoma is a small, benign (non-cancerous) growth in the pituitary gland, measuring less than 10 mm (1 cm). Cleveland Clinic notes that many are found by accident on brain imaging done for another reason, and that small ones often cause no symptoms. The next steps usually focus on whether it makes excess hormone, not on the size alone.

The pituitary is a small gland at the base of the brain that controls many other hormone glands, including the thyroid, adrenal glands, ovaries and testes. That is why a growth there, even a small one, leads to questions about hormones rather than only about the scan. Reports may use words such as 'lesion', 'focus', 'hypoenhancing area' or 'possible microadenoma'. Ask what the radiologist actually described and whether the finding is definite or uncertain.

Growths over 10 mm are called macroadenomas and are more likely to press on nearby structures. This guide covers the smaller, under-10-mm finding. It cannot tell you what your scan means; that needs your clinician.

Rarely, a pituitary growth can bleed or lose its blood supply suddenly. This is called pituitary apoplexy. The Pituitary Foundation describes it as an emergency that needs urgent hospital admission. Call local emergency services or go to an emergency department if you develop:

• a sudden, severe headache;
• sudden double vision, trouble moving the eyes, or loss of part or all of your vision;
• nausea and vomiting with the headache;
• drowsiness, confusion or reduced consciousness.

Yes. A growth found by chance is often called a pituitary incidentaloma. Cleveland Clinic states that adenomas may occur in as many as 20% of people at some point, and that most never cause symptoms or come to attention. Those found incidentally are usually small and do not produce hormones. The Pituitary Foundation notes that nonfunctioning tumours, which do not make hormones, are the most common type overall, accounting for about half.

Being common does not mean it should be ignored. The Endocrine Society guideline on pituitary incidentalomas recommends that everyone with one has a history, examination and blood tests, even without symptoms.

Some adenomas are 'functioning', meaning they release too much of a hormone. Others are 'nonfunctioning'. The scan cannot tell these apart, so blood tests are used. The Endocrine Society recommends screening for hormone excess and for low pituitary hormone levels.

MedlinePlus lists the tests that may be used, including:

If prolactin is high, remember that it has several possible causes besides a pituitary growth. A small adenoma that makes prolactin is called a microprolactinoma and is usually managed differently from other types; Cleveland Clinic notes that medicines are typically the first option for prolactinomas. Our high prolactin guide covers repeat testing and other causes in more detail.

• prolactin;
• IGF-1, to look for excess growth hormone;
• cortisol tests, which may use blood, urine, saliva or an overnight suppression test;
• thyroid tests (TSH and free T4);
• LH, FSH and testosterone or oestradiol.

The pituitary sits just below the nerves that carry vision from the eyes. Larger growths can press on them and narrow side vision. The Endocrine Society recommends a formal visual field test when the growth touches or presses on the optic nerves or chiasm.

Because most microadenomas are too small to reach these nerves, a vision test may not be needed. Ask whether your report mentions the optic chiasm, and report any new vision change straight away rather than waiting for the next scan.

For an incidental microadenoma that does not need surgery, the Endocrine Society suggests a repeat MRI at 1 year, then less often if the size stays the same. MedlinePlus also notes that small incidental tumours that cause no hormone problems can often be followed with repeat imaging.

Local practice varies, and the plan depends on the hormone results, any symptoms and how clear the first scan was. Ask who is responsible for booking the repeat scan and how you will hear the result.

Between scans, keep a simple record of any new symptoms. Changes worth reporting include new or different headaches, changes in side vision, periods becoming irregular or stopping, milky nipple discharge, reduced sex drive or erection problems, or unusual tiredness. MedlinePlus and the Pituitary Foundation list these among possible signs of hormone excess or reduced pituitary function. Report them to your clinician rather than waiting for the planned MRI.

Most nonfunctioning microadenomas are watched rather than treated. The Endocrine Society recommends referral for surgery in situations such as a visual field loss, pressure on the optic nerves, apoplexy with vision problems, or a growth that makes excess hormone other than prolactin. NCI and Cleveland Clinic describe surgery through the nose, medicines and radiation as the main treatments when they are needed.

Cleveland Clinic notes that adenomas need regular review and that one which keeps growing may eventually need treatment. If treatment is suggested, ask what it aims to achieve, what the alternatives are and what happens if you wait.

Bring the full MRI report and any blood results. These questions can help you leave with a clear plan.

• What size is it, and does it touch the optic nerves or chiasm?
• Which hormone tests have been done, and does it look functioning or nonfunctioning?
• Do I need a visual field test?
• When is the follow-up MRI, and who arranges it?
• Should I see an endocrinologist, and what symptoms should make me call before then?

On SameCase, patients and verified doctors share de-identified cases. Seeing how others with a pituitary microadenoma on MRI described their hormone tests, eye checks and follow-up scans can help you spot gaps in your own notes and prepare questions. Other people's cases cannot tell you what your scan means or what you should do; that remains with your clinician.