Pituitary Tumors

Pituitary adenomas are benign tumors which can cause symptoms through mass effect or hormone overproduction. Growth of a non-functional pituitary adenoma can put pressure on the optic nerves and brain, resulting in visual symptoms and related neurological problems. Alternatively, growth of hormonally active tumors can lead to overproduction of hormones normally produced by the pituitary gland, resulting in diseases caused by excessive growth hormone (acromegaly), ACTH (Cushing's disease) or prolactin. Surgery is the most effective treatment when visual problems are present, and rapid decompression with surgery often is successful in improving vision. Surgery is also frequently curative for small, hormone producing pituitary tumors. However, particularly when larger tumors are present, complete tumor removal is often not possible and tumor recurrence is common unless additional treatment is employed.

Certain hormone producing tumors, particularly prolactin secreting adenomas, can be successfully treated with medication. Medical management of growth hormone secreting tumors and ACTH secreting adenomas is less successful. For non-secreting tumors as well as certain hormone-producing tumors, conventional fractionated radiotherapy is usually administered when residual tumor remains after surgery. This treatment significantly reduces tumor recurrence rates, but is associated with suppression of normal pituitary function (hypopituitarism) in a significant percentage of patients.

Radiosurgery can prevent regrowth of residual tumor remaining after surgical decompression in a high percentage (>90%) of patients, resulting in long-term tumor control. Radiosurgery can also control hormone overproduction by pituitary tumors in many cases, although results vary depending on tumor type and length of follow-up, with the highest control rates reported for growth hormone producing tumors. A key advantage of radiosurgery is the strict limitation of radiation dose to the target volume, resulting in reduced risks of loss of normal hormone production (hypopituitarism) compared with conventional radiotherapy. However, certain pituitary tumors are too large or located too close to the optic nerves to be safely treated with radiosurgery; in general, the residual tumor must be less than 3 centimeters in size and located at least 3 millimeters from the optic nerves. Radiosurgery may also be used to treat patients whose tumors have recurred despite previous radiotherapy. The Perfexion Gamma Knife allows great precision in treating near the optic nerves.

References
Witt T. et al: Gamma Knife Radiosurgery for Pituitary Tumors. in Gamma Knife Brain Surgery. Prog Neurol Surg. Basel, Karger, 1998, vol 14, pp 114-127

Pollock B, et al: Stereotactic Radiosurgery for Pituitary Adenomas: Imaging, Visual and Endocrine Results. Acta Neurochirurgica-Supplemenum 1994;62:33-38