The pituitary gland, often called the “master gland,” is a small, pea-sized structure located at the base of the brain within a bony pocket called the sella turcica. As a central component of the endocrine system, it controls many essential bodily functions by releasing hormones that regulate other glands, such as the thyroid, adrenals, and gonads. A pituitary adenoma is a common growth arising from the cells of this gland. Understanding its unique location and behavior is central to understanding its effects on overall health and internal chemistry.
Defining the Pituitary Adenoma
A pituitary adenoma is a growth that originates specifically from the cells of the pituitary gland. While it is a tumor located inside the skull, it is technically not classified as a “brain tumor” because it does not arise from brain tissue, unlike growths such as gliomas or meningiomas. An adenoma is a tumor of the glandular tissue itself, and the vast majority—over 99%—are benign, meaning they are non-cancerous and do not spread to other parts of the body.
These growths are classified based on their size, which dictates how they might affect surrounding structures. Microadenomas measure less than one centimeter and usually remain within the confines of the sella turcica. Macroadenomas are larger, measuring one centimeter or more, and their increased size can lead them to press on nearby nerves and brain structures. Even though they are benign, macroadenomas can cause significant health problems due to their physical presence within the limited space of the skull.
Hormonal Effects of Adenoma Activity
Pituitary adenomas are divided into functional (secreting) and non-functional (non-secreting) types, based on whether they produce excess hormones. Functional tumors cause disease by overproducing a specific hormone, creating a state of hormonal excess that affects the entire body.
Functional Tumors
The most common type is a prolactinoma, which produces excess prolactin. This leads to symptoms such as irregular menstrual cycles and milky breast discharge in women, or reduced libido and erectile dysfunction in men. Other functional adenomas cause distinct medical conditions. Tumors producing excessive Adrenocorticotropic Hormone (ACTH) lead to Cushing’s disease, characterized by high blood pressure, weight gain, and a rounded face due to high cortisol levels. Excessive Growth Hormone (GH) production causes acromegaly in adults, resulting in abnormal growth of the hands, feet, and facial features. These hormone-producing tumors cause symptoms even when they are microadenomas.
Non-Functional Tumors
Non-functional adenomas do not secrete biologically active hormones and are often called “silent” tumors. They typically do not cause symptoms until they grow large and become macroadenomas. Their effect is primarily due to physical pressure, known as a mass effect. The growth can press on the optic chiasm, the structure where the optic nerves cross, often resulting in peripheral vision loss. Large adenomas can also compress surrounding healthy pituitary tissue, causing a deficiency in other pituitary hormones, a condition called hypopituitarism.
Detection and Diagnostic Procedures
The presence of a pituitary adenoma is often discovered in one of two ways: through symptoms caused by hormone excess or mass effect, or incidentally during an imaging scan for an unrelated condition. Patients experiencing hormonal symptoms or vision changes, such as a loss of side vision, prompt a targeted evaluation.
Diagnosis relies on a combination of anatomical assessment and hormonal evaluation. The gold standard for visualizing the tumor is a specialized Magnetic Resonance Imaging (MRI) scan of the pituitary gland. MRI uses contrast to provide detailed images of the tumor’s size, location, and relationship to the optic chiasm. This imaging helps differentiate the adenoma from other growths in the area.
Hormonal assessment involves blood and sometimes urine tests to measure the levels of various pituitary hormones and their targets. For example, a high prolactin level strongly suggests a prolactinoma, while tests for insulin-like growth factor-1 (IGF-1) screen for excess growth hormone. Specific tests, such as late-night salivary cortisol or a 24-hour urinary free cortisol measurement, are used to confirm excessive cortisol production in suspected ACTH-producing tumors.
Approaches to Management and Treatment
The management plan for a pituitary adenoma is highly individualized based on the tumor’s size, functional status, and the patient’s overall health and symptoms. For small, non-functional microadenomas that are not causing symptoms, the initial strategy is often “watchful waiting.” This involves regular hormonal and imaging surveillance to monitor for changes in size or the onset of symptoms before intervening.
Medical therapy is the first-line treatment for certain functional tumors, particularly prolactinomas. Dopamine agonist medications, such as cabergoline, are highly effective in shrinking prolactinomas and normalizing prolactin levels. Medication may also be used to control hormone levels for other functional tumors, often in preparation for or following surgery.
Surgery is the most common approach for macroadenomas causing mass effect, especially vision loss, and for functional tumors that do not respond well to medication. The preferred surgical technique is the transsphenoidal approach, where the tumor is removed through the nose and sphenoid sinus, avoiding the need for an open craniotomy. Radiation therapy is typically reserved as an adjuvant treatment for tumors that cannot be fully removed by surgery or for those that recur.