Located at the base of the skull, the pituitary gland serves as the body’s control center for hormones. Pituitary adenomas are slow growing, benign tumors within the gland.
Patients are diagnosed with an MRI scan and an endocrinological evaluation that determines whether hormone levels have been affected by the tumor. If the tumor is large, a visual evaluation may be needed as well.
Small tumors less than 1 centimeter are called microadenomas, while tumors larger than 1 centimeter are macroadenomas. Pituitary tumors are also divided into functioning and nonfunctioning varieties. As the terms imply, functioning tumors produce hormones, though often in large, unregulated amounts. Nonfunctioning tumors don’t produce significant amounts of hormones.
What are the symptoms?
Symptoms of pituitary adenomas depend on the type of hormone production affected by the tumor.
A tumor that produces large amounts of ACTH causes a condition known as Cushing Disease, which leads to obesity, high blood pressure, and muscle weakness, among other symptoms. A prolactinoma produces large amounts of prolactin. Symptoms include irregular menstruation, sexual dysfunction and breast discharge. A growth-hormone producing tumor leads to acromegaly, a condition that causes progressive enlargement of hands and feet as well as altered facial features.
A nonfunctioning adenoma leads to problems by compressing the pituitary gland and decreases or even cuts off normal hormone production.
Large tumors also can affect the optic nerves leading to a form of tunnel vision called bitemporal hemianopsia. In some cases, a pituitary adenoma causes headaches or a sensation of pressure or fullness behind the eyes. Rarely, bleeding into a tumor can lead to severe headaches, along with double and blurred vision.
What are the treatment options?
Medication can help correct hormone production with pituitary adenomas, though the gold-standard treatment is surgical removal. Doctors remove, or resect, as much of the tumor as safely as possible to eliminate pressure on the optic structures and remove parts of the tumor affecting hormone production.
Most pituitary surgeries don’t involve cutting into the skull. Surgeons access the gland through the sphenoid sinus, an air-filled space behind the nose, in a procedure known as transsphenoidal surgery. An incision is made either under the patient’s lip or inside the nose. A variation of the surgery using endoscopic assistance is even less invasive.
The major risk of transsphenoidal surgery is injury to the carotid arteries, to nearby tissues that affect vision or to healthy pituitary tissues that are often indistinguishable from the tumor. If the pituitary gland doesn’t function properly after surgery, the patient may require life-long hormone replacement.
Not all pituitary tumors require treatment. Sometimes a microadenoma is found on an MRI scan performed for other reasons. In such cases, a period of observation may be recommended. Treatment may be needed only when the microadenoma enlarges over time.
If the entire tumor can’t be removed surgically, radiation treatment may be needed to prevent its growth. Radiation may be an option for patients who are medically unable to undergo surgery or who oppose surgery.
Conventional radiation therapy uses a comparatively small number of radiation beams on the entire region around the pituitary gland, which usually results in a significant amount of normal, healthy tissue being irradiated as well. To compensate, conventional radiation treatment is given in daily doses over several weeks. The technique is generally effective in preventing tumor growth and in correcting hormone-producing tumors for many years.
Radiation therapy usually results in lower hormone production. Therefore, even if a pituitary adenoma doesn’t affect the patient’s hormone production, treatment with conventional radiation therapy can cause abnormally low hormone levels. In treating adenomas, conventional radiation therapy also irradiates nearby parts of optic tissues, though the risks of impaired vision are usually low.
A newer option for treating pituitary adenomas, radiosurgery focuses radiation on the tumor only, minimizing exposure to other tissues. Emerging data indicates radiosurgery may be more effective than conventional radiation in lowering abnormal hormone production and does so over a shorter time period.
Most radiosurgery techniques are one-time treatments, which increases the risk of some side effects, including vision loss. The risk of radiation injury is greater for patients when the tumor is close to or involves nearby optic tissues or part of the brain known as the hypothalamus. For higher-risk patients, staged, or fractionated, treatments may reduce the risk of injuring other tissues.
How effective is CyberKnife treatment?
Treating pituitary adenomas with the CyberKnife combines the advantages of conventional radiation and radiosurgery. Since CyberKnife performs radiosurgery, radiation exposure is limited to the adenoma. CyberKnife treatment can be fractionated, however, like conventional radiation therapy.
This approach lessens the radiation risk to sensitive structures around the tumor, like optic tissues and part of the brain known as the hypothalamus. CyberKnife fractionated stereotactic radiosurgery is also well suited for treating adenomas that invade the cavernous sinus, which contains nerves that control eye movement and facial sensation.
CyberKnife works best with:
- Patients with small tumors that overproduce a pituitary hormone
- Patients who have a residual tumor after transsphenoidal surgery
- Patients with hormone-producing tumors and who continue to have higher than normal hormone levels after surgery
- Patients with an adenoma that has invaded the cavernous sinus
- Patients who are unable to have or opposed to transsphenoidal surgery