Pituitary adenomas are remarkably common. Autopsy and radiological studies estimate that 14% to 23% of people have one, meaning roughly one in five or six adults is walking around with a small growth on their pituitary gland without knowing it. The vast majority of these never cause symptoms or require treatment.
How Prevalence Is Measured
The surprisingly high 14% to 23% figure comes from two types of studies: autopsies, where pathologists examine the pituitary gland after death, and imaging reviews, where researchers look at brain MRIs performed for other reasons. These numbers reflect all pituitary adenomas, including tiny ones that would never be noticed during a person’s lifetime.
When researchers look specifically at MRIs done on people without any suspected pituitary problems, the pooled detection rate is about 3.4%. The difference between that number and the autopsy figures makes sense: many adenomas are too small to show up on a standard brain scan but are visible under a microscope. In brain screening exams where no pituitary disease is suspected, the detection rate drops to less than 1%. But when imaging is performed because a doctor already suspects a pituitary issue, the rate jumps above 10%.
Clinically Diagnosed vs. Incidental
There is a wide gap between how many people technically have a pituitary adenoma and how many ever find out. Most of these growths are microadenomas, smaller than 10 millimeters, that sit quietly in the pituitary gland and produce no excess hormones. They are discovered incidentally when someone gets a brain MRI or CT scan for an unrelated reason, like a headache, head injury, or neurological workup. These are called pituitary incidentalomas.
A smaller subset of adenomas grow large enough or produce enough hormones to cause noticeable symptoms. These are the ones that lead to a clinical diagnosis. The published incidence rate has been rising in recent decades, largely because MRI technology has improved and more brain imaging is being performed for other conditions. More people aren’t developing pituitary adenomas; doctors are just finding more of the ones that were always there.
Types and Their Relative Frequency
Not all pituitary adenomas behave the same way. They are classified by whether they secrete hormones and, if so, which ones.
- Prolactinomas are the most common type, making up about 50% of all diagnosed cases. They overproduce prolactin, the hormone involved in breast milk production, and can cause irregular periods, unexpected breast discharge, and fertility problems in women. In men, the main symptom is reduced sex drive, which is often overlooked or attributed to other causes.
- Nonfunctioning adenomas account for roughly 30% of cases. These don’t secrete excess hormones. They typically cause problems only when they grow large enough to press on nearby structures, leading to headaches or vision changes.
- Growth hormone-secreting adenomas represent about 11% of cases. These cause a condition called acromegaly in adults, characterized by gradual enlargement of the hands, feet, and facial features.
- ACTH-secreting adenomas make up around 5% of cases. They drive the body to produce too much cortisol, leading to Cushing’s disease, which causes weight gain (particularly around the midsection and face), thinning skin, and easy bruising.
- TSH-secreting and gonadotropin-secreting adenomas are rare.
Who Gets Them
Pituitary adenomas can appear at any age, but diagnosed cases generally increase with age, at least up to about 80 years old. The pattern differs between men and women in an interesting way: women are diagnosed more often during their younger years, while men are diagnosed more often later in life. Overall, there is no significant difference in total incidence between the sexes.
The age and sex pattern largely reflects which symptoms are easiest to recognize. Prolactinomas, the most common type, cause menstrual irregularities and unexpected breast discharge in women. These are hard to miss and tend to prompt medical evaluation early. In men, the equivalent symptom is decreased libido, which is less specific and less likely to lead to a pituitary workup. As a result, men’s adenomas are often caught later, sometimes only when the tumor grows large enough to compress the optic nerves and affect vision.
Hereditary Cases
The vast majority of pituitary adenomas occur sporadically, with no identifiable genetic cause. A small fraction, estimated at roughly 2% to 4% of all cases, are linked to hereditary conditions. The best-known is familial isolated pituitary adenoma (FIPA), where multiple family members develop pituitary tumors without other associated hormone conditions. One study of over 1,000 pituitary tumor patients found a FIPA prevalence of about 1%.
Pituitary adenomas can also occur as part of broader genetic syndromes that affect multiple endocrine glands. These hereditary cases tend to appear at younger ages and sometimes behave more aggressively, but they represent a very small slice of total diagnoses. If you have a close family member with a pituitary adenoma, your individual risk is still low, though it may be worth mentioning to your doctor.
What the Numbers Mean in Practice
The high prevalence of pituitary adenomas can sound alarming, but context matters. The 14% to 23% figure includes every microscopic growth found on autopsy. The overwhelming majority of these are tiny, hormonally inactive, and would never cause a single symptom. For most people who have an incidental finding on a brain scan, the standard approach is periodic monitoring with follow-up imaging and hormone blood tests to confirm the adenoma isn’t growing or becoming active.
Among those whose adenomas do produce symptoms, treatment outcomes are generally favorable. Prolactinomas, the most common symptomatic type, typically respond well to medication that shrinks the tumor and normalizes hormone levels. Other types may require surgery, but even then, the pituitary gland’s location at the base of the brain allows surgeons to reach it through the nose without opening the skull, which shortens recovery considerably.
If you’ve been told you have a pituitary adenoma, the most useful question isn’t whether it’s common (it is) but whether it’s producing excess hormones and whether it’s growing. Those two factors, not the mere presence of the adenoma, determine whether any intervention is needed.