Radiosurgery an Effective Treatment for Benign Intracranial Tumors

Benign intracranial tumors occur about as often as primary malignant brain tumors. Most benign tumors are noninvasive, well defined, and well visualized on MRI and have a slow rate of progression. Each of these features makes them good candidates for radiosurgery — the single-session, focused delivery of radiation to an image-defined intracranial target.

The advantages of radiosurgery are that it can deliver a destructive dose of radiation to the target with little or no radiation effects on adjacent structures and that it is conducted in a single session.

Mayo Clinic neurosurgeons have performed radiosurgery for the past two decades. They have accumulated a depth of expertise and a vast database that includes patient characteristics, radiosurgical dosimetry and outcomes. Mayo Clinic in Minnesota alone has conducted 4,500 procedures, 35 percent of which have been for benign tumors of one of the following types: meningiomas, vestibular schwannomas, or pituitary adenomas. Control has been achieved in 95 percent of treated patients for these types of tumors.

Bruce E. Pollock, M.D., a Mayo Clinic neurosurgeon in Minnesota, notes that proper patient selection is critical. Across Mayo Clinic's three sites in Arizona, Florida, and Minnesota, patients are seen by neurosurgeons who have expertise in both open procedures and radiosurgery. Dr. Pollock recently reviewed more than 1,400 cases of meningiomas, vestibular schwannomas, and pituitary adenomas. He states that "when these types of benign tumors are small, occur in critical locations, have atypical or malignant features, or have recurred following previous surgery, radiosurgery is an excellent choice."

Mark K. Lyons, M.D., a neurosurgeon at Mayo Clinic in Arizona, adds that radiosurgery is well tolerated and of particular utility in elderly patients with medical conditions that put them at risk for an open procedure. He notes that radiosurgery does not preclude an open procedure should that be necessary at a later time. For that reason, when given the option many patients, regardless of age, choose radiosurgery to minimize the risk associated with open procedures.

Radiosurgery for Meningiomas

Studies have found that the rate of recurrence for a surgically removed meningioma is about 18 percent to 25 percent at 10 years. As Ronald Reimer, M.D., a neurosurgeon at Mayo Clinic in Florida, notes, "We've learned the importance of maintaining surveillance of meningiomas for a long period of time because they may recur or progress after many years of radiographic stability."

Radiosurgery has been found to reduce the risk of recurrence or progression. The two factors affecting both long- and short-term outcomes are tumor progression outside the field of radiation and tumor histology. Tumors that can be clearly imaged and those that are benign and without atypical histology have a far greater rate of success: Progression-free survival at five years as high as 100 percent in a series of 206 tumors at Mayo Clinic, compared with 83 percent for patients with atypical meningiomas.

Relative to brain site location, Mayo clinicians have found that radiosurgery is an effective therapy for cavernous sinus meningiomas except when there is symptomatic mass effect, an unusual clinical presentation, or nontypical features on imaging. Radiosurgery is typically not recommended for convexity and parasagittal meningiomas.

Vestibular schwannoma before and after radiosurgery

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Radiosurgery for Vestibular Schwannomas

Radiosurgery for small to moderate-sized vestibular schwannomas has been reported in several studies to improve the preservation of hearing and facial nerve function compared with surgical resection. This conclusion was supported by a Mayo Clinic study that compared surgical resection and radiosurgery for vestibular schwannomas with an average diameter of less than 3 cm. These Mayo investigators also found that the radiosurgical patients experienced less postprocedure dizziness.

Radiosurgery for Pituitary Adenomas

Radiosurgery is considered safe and effective for hormone-secreting pituitary adenomas. A major advantage of radiosurgery for these tumors compared with radiotherapy is that radiosurgery appears to shorten by more than half the time required to achieve biochemical remission and normalize hormone levels.

Controversy remains over whether pituitary suppressive medications at the time of surgery have a negative impact on tumor control. Several studies including a series of 46 acromegaly cases at Mayo Clinic, however, found that patients were more than four times as likely to reach normal hormone levels if they were off such medications before surgery.

Dr. Pollock notes that at Mayo Clinic patients with a pituitary adenoma that is both clearly defined and does not involve the optic apparatus are most often treated with radiosurgery. Patients in whom a pituitary tumor appears to be enlarging and who experience new or progressing visual field deficits, however, are referred for surgical resection.

"Small pituitary adenomas can often be treated successfully with surgery, but those that extend beyond the confines of the pituitary fossa and extend up toward the optic nerves or hypothalamus can be more difficult to remove entirely at surgery," notes Dr. Reimer.

A retrospective Mayo Clinic study of 62 patients with nonfunctional adenomas, 59 of whom had had prior tumor resection, found that with radiosurgery, the risk of new anterior pituitary deficits was 35 percent and that no patients experienced a decline in visual function.

Across Mayo's three sites, neurosurgeons have found that as an alternative to or in conjunction with traditional neurosurgery, radiosurgery is an effective, noninvasive option for treating benign intracranial tumors.