A pituitary tumor is an abnormal growth of tissue in an individual's pituitary gland, the small region in the brain responsible for keeping the delicate balance in hormone levels throughout the body. The pituitary gland produces hormones that tell all of the other hormones what to do and when to do it. A pituitary tumor can be cancerous or noncancerous, and it may or may not produce hormones. A pituitary tumor can produce excessive amounts of one or more hormones in the affected individual's body. A pituitary tumor can also destroy some of the healthy cells in the pituitary gland that are responsible for the secretion of hormones, resulting in underproduction of one or more hormones. Around three-fourths of all pituitary tumors inappropriately secrete hormones in the affected individual's body. Out of all tumors that develop in the skull, only fifteen percent are diagnosed as pituitary tumors.
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Multiple Endocrine Neoplasia
An individual affected by a pituitary tumor may also be affected by multiple endocrine neoplasia. Multiple endocrine neoplasias or MEN syndromes are endocrine system disorders that increase a patient's risk of developing noncancerous or cancerous tumors in the endocrine glands around the body. Pituitary tumors can be caused by multiple endocrine neoplasias because the most commonly affected glands in the endocrine system are the parathyroid gland, pancreas, adrenal glands, thyroid gland, and the pituitary gland. Pituitary gland tumors typically develop in multiple endocrine neoplasia type 1 (MEN1) patients. Multiple endocrine neoplasia type 1 occurs when a tumor suppressor gene called the MEN1 gene is mutated. The mutation causes the patient's body to be unable to produce a certain tumor-suppressing protein that is responsible for the downregulation of cell division to stop the development of tumors. The most common pituitary tumor in MEN1 is a prolactinoma.
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A McCune-Albright syndrome patient may develop a tumor in their pituitary gland as a complication of their rare disease. McCune-Albright syndrome is an uncommon disease that produces adverse effects on the structure and function of an individual's skin, endocrine system, and bones. McCune-Albright syndrome causes fibrous dysplasia in the bones, light brown patches of hyperpigmented skin, and an early onset of puberty. The thyroid gland in McCune-Albright syndrome patients can become enlarged and produce too much thyroid hormone. Because of the constant changes that occur in the endocrine glands of individuals affected by McCune-Albright syndrome, they are at an increased risk of developing a pituitary adenoma that secretes an excessive amount of growth hormone. One of the characteristic symptoms of McCune-Albright syndrome is the early onset of puberty due to an influx of hormones such as excess estrogen, testosterone, and growth hormone in the body.
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An individual who has developed a pituitary tumor may also be affected by Carney complex, which is an inherited genetic condition that causes an individual to experience skin pigment issues, the development of myxomas, and endocrine system tumors. Tumors that develop in Carney complex patients may be malignant or benign. Carney complex is the result of a genetic mutation on the PRKAR1A gene inherited from the affected individual's parents in an autosomal dominant manner. In a small number of cases of Carney complex, the genetic mutation occurs spontaneously. The most common type of pituitary tumor that develops in individuals with Carney complex is called a growth hormone-producing pituitary adenoma. This type of tumor in the pituitary gland initially develops from the somatotropic cells or the cells in the pituitary gland responsible for producing growth hormone. This type of pituitary tumor causes the excessive production of IGF1 from the liver and can lead to acromegaly and gigantism.
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An individual with a pituitary tumor may also have a family history of pituitary tumor development. The pituitary tumorigenesis in an individual can be the result of a number of abnormalities in the production of G-proteins. These abnormalities can run in families and have best been identified as ras-gene mutations, and any deletions, rearrangements, or mutations of the p53 gene. Along with the MEN1 gene abnormalities that cause an individual to have multiple endocrine neoplasias, some abnormalities can be passed from parent to child in the MEN4 gene that can cause an increased risk of developing a pituitary tumor. Another major running familial mutation identified as positively correlated with the development of pituitary tumors are those that occur in the AIP gene. In addition, a link has been found between patients who develop tumors in their pituitary gland and a maternal history of breast cancer. An individual who has a familial history of gigantism and or acromegaly is more likely to develop a tumor in the pituitary gland even if the pathophysiology of the direct family member's pituitary disorder is unknown.
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Genetic Mutations Later In Life
Some individuals develop tumors in their pituitary glands as a result of genetic mutations acquired later in their life, which can be due to a number of factors. The first factor known to play a role in pituitary tumorigenesis is an individual's hormone fluctuations throughout life. Genetic mutations that cause a pituitary tumor to develop can be caused by a post-menopausal phenomenon, such as post-menopausal periods. Patients who utilize hormone replacement therapy are also more likely to develop a mutation that causes the development of a pituitary tumor. For unknown reasons, individuals who gave birth at a young age are at an increased risk of developing a tumor in their pituitary gland later on in their life. A previous history of personal parathyroid, thyroid, colorectal, and adrenal tumors also causes an individual to be at a higher risk of developing tumors in the pituitary gland. In a small number of patients affected by pituitary tumors, a positive correlation was made with having had a twin pregnancy. A previous head injury or head trauma has predisposed some individuals to mutations that cause the development of a pituitary tumor.
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Vision loss is a complication that usually occurs with tumors that do not produce hormones or cause a deficiency of hormones the pituitary gland is responsible for producing. The reason behind this is symptoms of these types of pituitary tumors develop when the tumor is relatively small in size, where visual difficulties tend to occur when the tumor has grown to a larger size. Vision loss occurs when a pituitary tumor causes the optic chiasm or optic nerve to become compressed. The optic nerves are located in the area right above the pituitary gland, which makes them vulnerable to damage from a growing tumor. An affected individual may experience blurry, dim, or dark vision in one of their eyes if one of their optic nerves are being affected by the pituitary tumor. When a pituitary tumor presses on the optic chiasm in a certain way, patients may experience a loss of vision to the peripheral areas in both of their eyes.
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Apoplexy is cerebral bleeding or hemorrhage in the brain. Pituitary apoplexy is when an individual develops a pituitary adenoma that grows in a fashion that obstructs its own blood supply or spontaneously hemorrhages. Pituitary apoplexy causes acute swelling, bleeding in the brain, and tumor cell death. When tissues in the brain bleed, the increased pressure inside of the skull can cause the optic nerves, pituitary gland, and the nerves that control eye movement to become compressed. Symptoms of pituitary apoplexy include fever, stiff neck, hormone insufficiency, visual loss, nausea, vomiting, double vision, severe headache, and loss of consciousness. A CT scan and an MRI can detect pituitary apoplexy that has occurred due to a tumor in the pituitary gland.
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Permanent Hormone Deficiency
Permanent hormone deficiency is a term used to describe when the pituitary gland fails to make enough of the hormones it is responsible for producing. Permanent hormone deficiency may also be referred to as a permanent form of hypopituitarism in the medical community. Permanent hormone deficiency in the pituitary gland can be the result of a pituitary tumor causing damage to the hypothalamus, pituitary stalk, or pituitary gland itself. The most common hormones affected by pituitary tumor-precipitated permanent hormone deficiency include growth hormone, follicle-stimulating hormone, and luteinizing hormone. The cells in the pituitary gland responsible for secreting thyroid-stimulating hormone and adrenocorticotropic hormone are not as susceptible to permanent hormone deficiency. Individuals who have pituitary tumors greater than two centimeters in diameter are more likely to be affected by permanent hormone deficiency.