41 Stereotactic Radiosurgery for Meningiomas: Techniques and Results
This textbook addresses the many issues surrounding meningiomas. From anatomical and pathological considerations to imaging and natural history, clinical context based on age, adjuvant therapies, and surgical resection stratified by brain or spine location, one meningioma may be very different from another. These common tumors pose a variety of therapeutic challenges because of these issues. Over the past century, craniotomy and tumor resection along with the tumor’s dural base became the preferred approach for the majority of symptomatic patients with intracranial tumors.1 Over time, the morbidity of resection was reduced with microneurosurgical technique, better anesthesia, neuronavigation, and improved medical care. These achievements have been discussed. However, because these usually benign tumors may be associated closely with critical neural or vascular structures, complete resection may not be feasible.2–5 Meningiomas adjacent to venous sinuses may be resectable only at the risk of major neurological deficits caused by venous injury. Elderly or infirm patients often seek alternative approaches. This chapter reviews our experience in the care of over one thousand patients with intracranial meningiomas using stereotactic radiosurgery. We have found that our approach provides safe and effective management of these tumors when properly selected.
During our first 20 years of experience, radiosurgery was performed on 1191 intracranial meningiomas. Our first report was in 1991, when we detailed results from the first 50 patients.6 We recently reviewed results from the initial 972 patients with 1045 tumors managed over the initial 18 years.7 The brain locations of these tumors are shown in Table 41.1 . The decision to perform radio-surgery was made in patients with residual or recurrent smaller volume tumors after prior resection, those with symptomatic primary tumors in locations associated with higher risk for resection, those with concomitant medical illnesses or advanced age, those in younger patients who chose radiosurgery over other available options, and those in younger patients with minimal symptoms or who were asymptomatic but chose against observation. There are some relative contraindications or exclusion criteria for radiosurgery. These include large tumor volume (mean diameter > 3.5 cm), tumors with symptomatic optic nerve or chiasmal compression, optic nerve sheath tumors with preserved vision, elderly patients with asymptomatic tumors, or tumors with atypical imaging features and no prior histologic diagnosis.
The detailed results from 982 tumors (94%) were available for analysis. Five hundred and four patients (51%) had had no prior treatment, and prior resections were usually partial removals (84%). A solitary tumor was present in 818 patients, and multiple tumors were found in 161. Twenty-eight patients had neurofibromatosis type 2. Tumor pathology was studied in 511 residual or recurrent tumors. Prior radiotherapy (RT) had been delivered to 54 patients (48 after a resection, and six had RT alone); two patients had prior radiosurgery elsewhere. Eight patients had received chemotherapy. Twenty-five tumors (2.5%) developed after prior fractionated irradiation.
Radiosurgery was performed under local anesthesia with mild sedation as necessary, using a Leksell Gamma Knife (Elekta, Inc., Norcross, GA). We have used the Gamma Knife models U, B, C, 4C, and Perfexion for our patients with meningiomas. Radiosurgery was targeted with stereotactic computed tomographic (CT) guidance (before 1992), and with magnetic resonance imaging (MRI) since. A mean of 7.5 isocenters were used to provide conformal radiosurgery. The dose received by adjacent critical structures was determined, and selective beam blocking used if necessary to restrict the dose fall-off ( Fig. 41.1 ). We delivered a mean dose to the tumor margin of 14 Gy and a mean maximum dose of 28 Gy. The mean tumor volume in this series was 7.4 mL. The mean volume receiving ≤ 12 Gy was 8.4 mL. Radiation doses were prescribed to the 50% isodose volume for 886 tumors (85%) ( Fig. 41.2 ). For tumors near the optic nerve or chiasm, the average maximal optic dose was 6.4 Gy. After radio-surgery, patients were discharged home within 24 hours, and in recent years on the same day. The median follow-up in this study was 4 years; 842 patients were still living (86%). Follow-up past 5, 7, 10, and 12 years was obtained in 327, 190, 90, and 41 patients, respectively.
Number of Tumors
Tumor Response to Radiosurgery
Imaging studies after radiosurgery showed that 407 tumors had regressed, 454 were unchanged, and 96 had enlarged, for a raw tumor control rate of 90% ( Fig. 41.3 ). Imaging and clinical follow-up were requested for all patients but were not complete for all.
Based on prior histopathology, we had 424 World Health Organization (WHO) grade I meningiomas in this series, and 384 were available for study. We found that 172 tumors had regressed, 186 were unchanged, and 26 had enlarged, for a tumor control rate of 93%, at a median of 4 years. Ninety-one percent of patients were either improved (n = 21), or unchanged (n = 341) clinically. Imaging follow-up past 8 and 10 years was obtained in 79 and 53 tumors, respectively, both with a control rate of 91% ( Figs. 41.4 and 41.5 ). Past 10 years, 45 patients were stable, six were improved, and two were worse. For grade I meningiomas, the 5-, 10-, and 15-year actuarial tumor control rates were 97 + 1.2%, 87.2 + 4.4%, and 87.2 + 4.4%. Disease-specific survival was 98.9 + 0.5%, 96.2 + 1.9%, and 96.2 + 1.9%, respectively.
Of 56 WHO grade II tumors, 54 were available for review. Sixteen had regressed, 11 were unchanged, and 27 had enlarged for a tumor control rate of 50%, at a median of 2 years. During follow-up, 72% of these patients were stable clinically. Of 31 WHO grade III tumors, 29 were reviewed. We found that four regressed, one was stable, and 24 later enlarged, for a tumor control rate of 17% at a median of 15 months.