Lying behind and between the eyes at the base of the brain, the pea-sized pituitary gland secretes hormones into the bloodstream. Most tumors of the pituitary gland are slow-growing and benign. Nonetheless, they may cause serious, uncomfortable side effects if left untreated.
Some potential side effects are caused by hormones secreted by the tumor itself. These tumors, called "functioning tumors," contribute to an excess of one or more hormones circulating in bloodstream. "Non-functioning tumors" lack the capacity to secrete hormones, but cause problems when they grow in a way that impinges upon healthy cells.
Functioning pituitary tumors
Patients with functioning or homone-secreting tumors generally require immediate relief of their symptoms, which may include hypertension and diabetes. Pituitary tumors are named after the hormone they secrete. Prolactin-secreting tumors, for example, secrete the hormone prolactin and often can be successfully treated with medication only. Other hormone-secreting tumors are often treated with microsurgery.
Gamma Knife radiosurgery is ideally suited for situations in which the tumor is incompletely removed, recurs, or can’t be safely resected during microsurgery. In these cases, elevated hormone levels generally decrease within six to 12 months following Gamma Knife radiosurgery. Hormone secretion returns to normal in 50 to 90 percent of cases, depending on the type of tumor.
Symptoms of functioning pituitary tumors vary according to the hormone secreted by the tumor cells:
Prolactin (PRL) - Excess PRL prodcution causes inappropriate production of milk (galactorrhea), irregular menstual cycles or cessation of menses (amenorrhea) and infertility. In men, excess PRL leads to impotence and infertility.
Growth Hormone (GH) - In children, excess production leads to gigantism. In adults, it leads to enlargement of the hands, feet and jaw (acromegaly). In addition, these patients may suffer from diabetes mellitus, hypertension, heart disease and arthritis.
Adrenocorticotropic Hormone (ACTH) - ACTH stimulates the adrenal gland to secrete cortisol. Excess cortisol (Cusing's disease) causes excessive fat buildup in various areas, including the face, neck and abdomen. Other symptoms include thin skin, easy bruising, diabetes mellitus, hypertension and excessive hair growth.
Thyroid Stimulating Hormone (TSH) - Excess TSH production leads to hyperthyroidism, which manifests in rapid heart beats, hypertension, irritability, weight loss and intolerance to heat.
Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) - In women, FS and LH help regulate egg production by the ovaries and control the menstrual cycle. In men, these hormones help regulate the testes' production of sperm and testosterone. Excess production can lead to abnormalities with these functions.
Non-functioning pituitary tumors
Non-functioning or non-secreting tumors are characteristically slow-growing. However, excessive growth can lead to insufficient production of one or more hormones, or compression of the visual nerves. These tumors can grow to be quite large and are usually found only when symptoms of compression are noted. Loss of peripheral vision is often the first sign.
Microsurgery is commonly used to treat non-functioning tumors. Afterwards, if the residual tumor is small, close observation is all that is needed. If a previously resected tumor recurs, further surgery, radiosurgery, or fractionated radiation therapy may be required.
In select cases, Gamma Knife radiosurgery has the advantage of delivering a high dose of radiation in a single fraction while minimizing the risk of damage to the nearby visual nerves and normal pituitary gland cells. Overall, Gamma Knife radiosurgery has a very high chance of preventing further tumor growth – and in some cases shrinking the residual tumor – with very little risk of visual loss or damage to the hypothalamus.
Gamma Knife radiosurgery after microsurgery
Radiosurgery is not recommended for tumors that elevate and compress the visual nerves because of the risk of injury to these nerves. However, in cases where microsurgery has successfully reduced the tumor near the optic apparatus, Gamma Knife may be used to treat the residual tumor.
