Positive outcomes from Gamma Knife Radiosurgery in posterior fossa meningiomas

Meningiomas are the most common benign intracranial tumors, and in individuals ages 35 and older, the most common type of brain tumor diagnosed. They most often occur in people between the ages of 40 and 70. They originate from cells (arachnoid cap cells) within the arachnoid, a thin, spider web-like membrane that surrounds the brain and spinal cord. Although the majority of meningiomas are benign, undiscovered these tumors can grow slowly until they are very large, and in some locations, can be severely disabling and even life threatening.

Meningiomas of the posterior cranial fossa encompass approximately 7-12 percent of intracranial meningiomas. For symptomatic or progressive lesions, complete surgical resection is the optimal primary treatment when possible. Depending on their location, a complete surgical resection can be difficult as tumors are often in close proximity to critical vascular and neural structures. Although numerous studies have analyzed the role of stereotactic radiosurgery for intracranial meningiomas, few studies have assessed factors associated with outcome and remission of posterior fossa meningiomas.

Researchers at the University of Virginia, Charlottesville, analyzed factors predictive of outcomes and recurrence in patients with posterior fossa meningiomas treated with Gamma Knife® Radiosurgery. The results of this study, Gamma Knife Radiosurgery of Meningiomas Located in the Posterior Fossa: Factors Predictive of Outcome and Recurrence, will be presented by Robert M. Starke, MD, 4:01-4:15 pm, Monday, April 11, during the 79th Annual Scientific Meeting of the American Association of Neurological Surgeons in Denver. Co-authors are James H. Nguyen, BS, Jessica Rainey, BS, Brian J. Williams, MD, Jonathan H. Sherman, MD, Jesse Savage, MD, PhD, Chung Po Yen, MD, and Jason P. Sheehan, MD, PhD. Dr. Starke will be presented with the Leksell Radiosurgery Award for this research.

The authors analyzed outcomes in 152 patients with posterior fossa meningiomas treated with Gamma Knife Radiosurgery (GKRS) at the University of Virginia from 1990 to 2006. Additional patient demographics:

•Gender: 122 females, 30 males
•Median age: 58 years (range 12-82)
•Median follow-up: 7 years (range 2-16 years)
•Meningioma location: Centered over the tentorium (35, 23 percent); cerebellopontine angle (43, 28 percent); petroclival region (28, 18 percent); petrous region (6, 4 percent); and clivus (40, 26 percent)
•GKRS was used as the first surgical method in 75 patients; 77 patients were treated with GKRS following surgical resection.
•Pre-radiosurgery tumor volume: 5.7 cc (range 0.3-33c)

Patients were followed clinically and radiologically every six months for the first year, once a year until five years post radiosurgery, and then every two years thereafter. At each follow-up visit, a neurological examination was performed to check for new neurological deficits, and neuroimaging studies were reviewed to assess tumor response. A decrease or increase in tumor size was defined as a 15 percent or greater change in tumor volume when compared to the volume at the time of GKRS. The analysis yielded the following data:

Radiologic Dosage and Outcome

•Mean maximum dose to the tumor: 34 Gy (range 12-60 Gy); Mean tumor margin dose: 14 Gy (range 8-25 Gy); mean prescription isodose line: 43 percent (range 25-60).
•Post-radiosurgery tumor volume: 4.9 cc (range 0.1-33c).
•Fifty-five (36 percent) patients showed no change in tumor volume, 78 (51 percent) showed a decrease in volume, and 19 (13 percent) patients showed an increase in volume.
•Radiographic progression free survival at 3, 5, and 10 years was 98 percent, 96 percent, and 78 percent, respectively.

Clinical Outcome

•Symptom progression: 139 patients (91.4 percent) showed no symptom change or improvement; 13 (8.6 percent) patients deteriorated.
•Three patients required ventriculoperitoneal shunts to treat GKRS-related hydrocephalus.
•Seven patients (4.6 percent) required surgical resection following GKRS.

"Our research yielded some important data about factors which impact the progression and recurrence of posterior fossa meningiomas. We found that if the tumor was located in clivial or petrous locations, this was a predictor of worsening symptoms following GKRS. Previous studies have theorized that older patients with meningiomas most likely have slow growing lesions with longer survival rates. Our analysis, however, found that pre-GKRS covariates predictive of tumor progression included age greater than 65 and smaller peripheral dose. What remains to be determined in future studies is whether older patients might have a predisposition to develop a type of tumor that is more likely to progress," said Dr. Starke.

"Radiosurgery is an alternative treatment for posterior fossa meningiomas in patients who have operative risks including advanced age, those who refuse microsurgery, or those with residual or recurrent tumors. GKRS offers an acceptable rate of tumor control for posterior fossa meningiomas with a low incidence of neurological deficit side effects," concluded Dr. Starke.