Pituitary adenomas are benign (noncancerous) tumors of the pituitary gland - a small structure located behind the eyes, beneath the brain. Most pituitary tumors are benign, meaning that they do not spread to distant locations in the body. Cancerous pituitary tumors are extremely rare.
The pituitary gland is a principal part of the endocrine system (the set of glands and organs that produce hormones). The pituitary is called the “master endocrine gland,” because it produces specific hormones that control the activities of other endocrine glands and organs in the body.
Pituitary adenomas usually develop in older adults, but they may occur in children. These tumors are very common, occurring in up to 20% of adults. Although most pituitary adenomas are harmless, some cause serious problems. Typically, a pituitary adenoma develops in the anterior pituitary, and its impact is determined by its size and whether it secretes hormones.
Types of Pituitary Adenomas
Functional (hormone-producing) pituitary adenomas excessively secrete one or more hormones - prolactin, growth hormone (GH), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH).
Nonfunctional pituitary adenomas do not secrete hormones.
Macroadenomas are large (>1 centimeter) and may compress adjacent structures, causing serious complications such as loss of vision. Large tumors impair the pituitary’s function, causing hormone deficiencies (hypopituitarism).
Microadenomas are small (<1 centimeter) and rarely compress nearby tissues, but they can be harmful if they secrete excessive hormones.
Classification of Functional Pituitary Adenomas
Prolactin-secreting adenomas (prolactinomas) are the most common type, and they cause hyperprolactinemia.
Growth hormone-secreting adenomas cause acromegaly in adults or gigantism in children.
Adrenocorticotropic hormone (ACTH)-secreting adenomas cause Cushing’s disease.
Thyroid-stimulating hormone (TSH)-secreting adenomas are rare and lead to hyperthyroidism.
Gonadotropin (LH and FSH)-secreting adenomas are very rare and cause reproductive dysfunction.
The underlying cause of pituitary adenomas is unknown, and there are no lifestyle or environmental factors that increase a person’s risk of developing this condition. Rare cases are linked to inherited genetic syndromes.
The signs and symptoms of pituitary adenomas correlate with the tumor size and whether excess hormone is secreted. The onset of symptoms is gradual and early symptoms may go unnoticed for years.
Excess ACTH stimulates the adrenal glands to overproduce cortisol (Cushing’s disease). Normally, cortisol maintains blood pressure and helps the body react to stressful conditions; however, too much cortisol disrupts numerous bodily functions.
Excess gonadotropins (LH and FSH) disrupt reproductive processes.
Menstrual period changes
Low testosterone level in males
Loss of libido.
Large pituitary adenomas may cause headaches, nausea, and vomiting. Compression of the optic chiasm causes loss of peripheral vision. Injury to the posterior pituitary impairs antidiuretic hormone (ADH) production (a condition known as diabetes insipidus) and leads to excess urination, dehydration, and thirst. Additional pituitary hormone deficiencies cause infertility.
Functional microadenomas are tiny, but they cause problems by secreting excessive hormones. Conversely, small, asymptomatic nonfunctional adenomas (so-called incidentalomas) are usually found on MRIs performed for other reasons.
Several tests are used to diagnose pituitary tumors.
Visual Field Examination - Compression of the optic chiasm causes a loss of peripheral vision on both sides.
Hormone Testing - Blood, urine, and saliva are tested for abnormal hormone levels. Hormone levels are also tested in response to certain hormone-suppressant medications.
Imaging Studies - Magnetic resonance imaging (MRI) of the pituitary provides detailed pictures of the gland and surrounding structures. Computed tomography (CT) may also be obtained.
Surgery is the predominant treatment for pituitary adenomas. Treatment is important for functional or large tumors; however, small, asymptomatic nonfunctional adenomas (incidentalomas) are closely watched and not necessarily treated unless they grow.
Pituitary Surgery: Most pituitary adenomas are removed through the nose (transsphenoidal approach). This approach allows neurosurgeons to remove the tumor without entering the brain. Surgery is usually more successful for small tumors than large ones. Postoperative complications include hormone deficiencies such as low ACTH (secondary adrenal insufficiency) characterized by low cortisol, low blood pressure, low blood sugar, hair loss, and loss of libido. Some patients develop low vasopressin, which causes diabetes insipidus. These complications are treated with hormone replacement medications. Additional complications may include infection of the linings of the brain (meningitis), or leakage of cerebrospinal fluid from the nose.
Medications: Sometimes medications are prescribed in lieu of surgery or for treatment of complications after surgery. Medications are available to block the production of excess hormones or correct hormone deficiencies.
Radiation Therapy: Radiation is used to destroy the tumor when surgery alone is inadequate or when a patient is a poor candidate for surgery. External radiation treatments are administered over a period of weeks. Another method, called Gamma Knife stereotactic radiosurgery, uses a focused beam of radiation directly precisely at the pituitary tumor. Radiation therapy does not provide immediate results and patients may take years to achieve the full effect.
Pituitary adenomas are not associated with any known lifestyle or environmental risk factors, so there are no available methods to prevent the condition. People with a family history of pituitary tumors associated with inherited genetic syndromes should be regularly monitored for early signs of the disorder.
Melmed S, Kleinberg D. Chapter 9. Pituitary Masses and Tumors. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology, 12e. Philadelphia, PA: Elsevier Saunders; 2011.
Pituitary Tumors. American Cancer Society website. http://www.cancer.org/cancer/pituitarytumors/detailedguide/pituitary-tumors-what-causes. Accessed May 15, 2014.
Pituitary Disorders. Johns Hopkins Medicine website. http://www.hopkinsmedicine.org/neurology_neurosurgery/specialty_areas/pituitary_center/conditions/. Accessed May 15, 2014.
Tina is a Life Science Writer for a number of online publications, including Innerbody.com. Her expertise is in conveying complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. In her spare time, she enjoys drawing science-related cartoons.