A pituitary lesion is any abnormal growth or structural change in or near the pituitary gland, a pea-sized gland at the base of the brain that controls hormone production throughout the body. Most pituitary lesions are benign tumors called adenomas, but the term also covers fluid-filled cysts, inflammatory conditions, and rare cancerous growths. They are surprisingly common: autopsy studies find pituitary lesions in roughly 10.7% of people, and MRI-based studies detect them in about 3.4% of the general population, meaning many people carry one without ever knowing.
Types of Pituitary Lesions
The most common type by far is the pituitary adenoma, a slow-growing, noncancerous tumor of the anterior (front) portion of the gland. Adenomas fall into two broad categories. Functioning adenomas actively produce excess hormones and tend to cause symptoms earlier, when they’re still relatively small. Nonfunctioning adenomas don’t secrete hormones on their own, so they often grow larger before anyone notices them. In one comparative study, nonfunctioning tumors had an average volume roughly 50% greater than their functioning counterparts by the time of diagnosis.
Beyond adenomas, other lesions can develop in the same area. Rathke cleft cysts are fluid-filled sacs that form from leftover tissue during fetal development. They typically appear as well-defined cystic structures on imaging and are often found incidentally. Craniopharyngiomas are more complex growths that may contain both solid and calcified components. They carry a higher chance of causing hormone deficiency and neurological problems, with up to 95% of patients showing some degree of pituitary hormone loss at diagnosis. Doctors also watch for vascular issues like aneurysms and, rarely, hemorrhage within the gland itself.
Symptoms From Hormone Overproduction
When a functioning adenoma pumps out too much of a specific hormone, the symptoms depend on which hormone is involved.
Prolactin-secreting tumors (prolactinomas) are among the most common functioning adenomas. In women, excess prolactin disrupts menstrual cycles, causes missed periods, can trigger unexpected breast milk production, and reduces fertility. Men experience reduced sex drive, erectile dysfunction, and infertility. Because these symptoms are noticeable, prolactinomas are often caught while still small.
Growth hormone-secreting tumors lead to a condition called acromegaly in adults. Classic signs include enlargement of the hands, feet, and jaw, excessive sweating, headaches, and glucose intolerance. Over time, unchecked growth hormone excess can cause joint problems, diabetes, high blood pressure, and heart or respiratory complications.
ACTH-secreting tumors drive the adrenal glands to produce too much cortisol, resulting in Cushing’s disease. This causes weight gain (especially around the midsection), severe fatigue, muscle weakness, high blood pressure, thinning skin with purplish stretch marks, mood changes, and impaired blood sugar control. Chronic cortisol excess also raises the risk of blood clots and cardiovascular disease.
Symptoms From Size and Pressure
Nonfunctioning lesions, and large functioning ones, cause problems by pressing on surrounding structures. The pituitary sits in a small bony pocket directly below where the two optic nerves cross, so growth in this area can squeeze those nerves. Up to 75% of patients with significant compression develop visual impairment, most commonly losing peripheral vision on both sides, a pattern called bitemporal hemianopia. In rare cases, blindness can occur. About 42% of people with nonfunctioning adenomas first notice something is wrong because of eye symptoms.
Larger lesions can also press on nearby cranial nerves that control eye movement. Roughly half of patients with substantial pressure effects develop some degree of eye movement difficulty. The nerve most frequently affected is the one that controls upward, downward, and inward eye movement along with eyelid opening, leading to drooping eyelids, double vision, or an eye that drifts outward.
Pressure on the healthy pituitary tissue itself can reduce normal hormone output, causing fatigue, low thyroid function, adrenal insufficiency, or problems with reproductive hormones. Persistent headaches are another common complaint, even with moderately sized lesions.
How Pituitary Lesions Are Diagnosed
Many pituitary lesions are discovered accidentally during brain imaging done for an unrelated reason, such as a head injury or chronic headaches. These incidental findings are called pituitary incidentalomas. Once a lesion is found, two things need to happen: detailed imaging and a thorough hormone evaluation.
The standard imaging study is an MRI of the sellar region (the bony pocket where the pituitary lives), using a contrast agent to highlight the gland’s structure. This reveals the lesion’s exact size, location, and relationship to surrounding tissues like the optic nerves. It also helps distinguish between an adenoma, a cyst, an aneurysm, or hemorrhage. MRI can pick up features like calcification or solid components that point toward a craniopharyngioma rather than a simple cyst.
Blood tests measure the full panel of pituitary hormones and the hormones they regulate downstream. Doctors check cortisol and its controlling hormone ACTH, growth hormone and its marker IGF-1, prolactin, thyroid-stimulating hormone alongside thyroid hormone levels, and the reproductive hormones LH and FSH along with testosterone or estrogen. If the lesion is overproducing a hormone, levels will be abnormally high. If it’s compressing healthy pituitary tissue, one or more hormone levels will be abnormally low.
Treatment Approaches
Treatment depends on the type of lesion, whether it produces hormones, and how much pressure it puts on nearby structures.
Prolactinomas are unusual among pituitary tumors because they typically respond well to medication. Drugs that mimic dopamine’s action can shrink these tumors and normalize prolactin levels, often making surgery unnecessary. Growth hormone-secreting and TSH-secreting tumors can also be managed with medications that suppress hormone release, though surgery is more commonly part of the plan.
For most other pituitary adenomas, particularly nonfunctioning tumors causing vision loss or significant hormone disruption, surgery is the primary treatment. The standard technique is transsphenoidal surgery, which reaches the pituitary through the nasal passages and the thin bone at the back of the sinuses. This avoids opening the skull and generally allows for a shorter recovery. Outcomes are good when performed by experienced surgeons, and most patients go home within a few days.
Small, nonfunctioning lesions that aren’t causing symptoms or hormone changes are often simply monitored with periodic MRI scans and blood work. Many of these never grow or cause problems.
Pituitary Apoplexy
One complication worth knowing about is pituitary apoplexy, a sudden bleed or loss of blood supply within a pituitary tumor. It causes a severe, abrupt headache (typically felt behind the eyes), sudden vision changes, double vision, nausea and vomiting, and sometimes confusion or loss of consciousness. Blood pressure and heart rate may drop, and body temperature can fall. About 80% of patients experiencing apoplexy have a deficiency in at least one pituitary hormone at the time it happens.
Apoplexy is a medical emergency. Diagnosis relies on urgent neuroimaging. A CT scan is usually done first because it’s fast and can show bleeding within the gland. An MRI follows to define the full extent of the damage, identifying both hemorrhagic and necrotic tissue. Treatment may involve emergency surgery to relieve pressure, along with hormone replacement to stabilize the body’s critical functions.