Stereotactic radiosurgery (SRS) has been performed for intracranial meningiomas for more than 30 years. Small to moderate-sized meningiomas are generally considered good candidates for SRS because of their neuro-imaging and radiobiological characteristics. Patient selection is critical for successful meningioma SRS. Factors related to tumor control and radiation-related complications in patients with WHO grade I or presumed meningiomas include history of prior surgery, tumor volume, and tumor location. Patients with small volume, nonoperated skull-base or tentorial meningiomas typically have the best outcomes after SRS.
Key points
- •
Meningiomas are typically well visualized on magnetic resonance imaging, facilitating complete radiosurgical coverage.
- •
A tumor margin dose from 12 to 15 Gy provides a high rate of tumor control and a low complication rate for well-selected patients with World Health Organization (WHO) grade I intracranial meningiomas. Higher doses are typically used when safe for patients with WHO grade II or III meningiomas.
- •
Tumor control is higher for WHO grade I meningiomas (≈95% at 5 years) compared to WHO grade II (≈60% at 5 years) and 10% for WHO grade III (≈10% at 5 years) meningiomas.
- •
Increasing tumor volume, prior or concurrent external beam radiation therapy, and location are important predictors of radiation-related complications. Meningiomas of the skull base or tentorium have a lower risk of radiation-related complications compared with convexity or falx meningiomas.
Introduction
Meningiomas are the most common nonglial tumor affecting the central nervous system. Although meningiomas have been described by earlier neurosurgeons, it was not until Cushing and Eisenhardt in 1938 detailed the clinical presentation, pathology, and surgical treatment that these tumors were more clearly understood. Based on the work and teachings of Dr Cushing, surgical excision became the preferred treatment for patients with symptomatic, intracranial meningiomas. In 1957, Simpson published his landmark article describing 5 grades of meningioma removal that demonstrated the relationship between the aggressiveness of meningioma resection and later tumor recurrences. A grade 1 resection is a complete macroscopic tumor removal with excision of its dural attachments and adjacent abnormal bone. Grade 2 is a complete macroscopic tumor removal with coagulation of its dural attachments. Grade 3 is a complete macroscopic removal of the tumor without resection or coagulation of its dural attachments or extradural extensions. Grades 4 and 5 are partial tumor resection and simple decompression, respectively. The rate of symptomatic meningioma recurrence was 9%, 19%, and 29% for patients having grades 1, 2, and 3 resections, respectively. Simpson concluded that surgery for intracranial meningiomas should be as extensive as possible, understanding that complete tumor removal is often not feasible for many skull-based tumors or for patients with tumors attached to the venous sinuses. Over the past 50 years, neurosurgeons have embraced this attitude, creating the foundation used in the management of meningioma patients.
Advances in anesthesia, neuroimaging, and microsurgical techniques have increased the number of patients having complete resection of their meningiomas with acceptable morbidity. However, some meningiomas invade the adjacent neurovascular structures and cannot be completely removed. Consequently, most neurosurgeons now recommend subtotal (nonradical) tumor resections for critically located meningiomas as a method to reduce symptomatic mass effect at less risk than a complete tumor resection. Nevertheless, even when a meningioma has been completely removed, the tumor recurrence rates may be as high as 15% at 5 years. For patients with benign meningiomas (World Health Organization [WHO] grade I) having tumor recurrence or progression, external beam radiation therapy (EBRT) has been used for many years as a postoperative adjunct to provide tumor growth control, and also for patients with atypical (WHO grade II) or malignant (WHO grade III) meningiomas. Numerous studies have documented that postoperative EBRT decreases tumor recurrence and improves survival for patients after incomplete meningioma resection. Despite improving progression-free survival (PFS) for meningioma patients, EBRT requires 5 to 6 weeks and can result in cognitive decline, radiation-induced neoplasms, or pituitary insufficiency.
As an alternative to surgical resection or EBRT, stereotactic radiosurgery (SRS) has been used for more than 30 years for patients with intracranial meningiomas. In this article, the tumor control and complication rates for patients with intracranial meningiomas having single-fraction SRS at the authors’ center from 1990 until 2008 are discussed.
Introduction
Meningiomas are the most common nonglial tumor affecting the central nervous system. Although meningiomas have been described by earlier neurosurgeons, it was not until Cushing and Eisenhardt in 1938 detailed the clinical presentation, pathology, and surgical treatment that these tumors were more clearly understood. Based on the work and teachings of Dr Cushing, surgical excision became the preferred treatment for patients with symptomatic, intracranial meningiomas. In 1957, Simpson published his landmark article describing 5 grades of meningioma removal that demonstrated the relationship between the aggressiveness of meningioma resection and later tumor recurrences. A grade 1 resection is a complete macroscopic tumor removal with excision of its dural attachments and adjacent abnormal bone. Grade 2 is a complete macroscopic tumor removal with coagulation of its dural attachments. Grade 3 is a complete macroscopic removal of the tumor without resection or coagulation of its dural attachments or extradural extensions. Grades 4 and 5 are partial tumor resection and simple decompression, respectively. The rate of symptomatic meningioma recurrence was 9%, 19%, and 29% for patients having grades 1, 2, and 3 resections, respectively. Simpson concluded that surgery for intracranial meningiomas should be as extensive as possible, understanding that complete tumor removal is often not feasible for many skull-based tumors or for patients with tumors attached to the venous sinuses. Over the past 50 years, neurosurgeons have embraced this attitude, creating the foundation used in the management of meningioma patients.
Advances in anesthesia, neuroimaging, and microsurgical techniques have increased the number of patients having complete resection of their meningiomas with acceptable morbidity. However, some meningiomas invade the adjacent neurovascular structures and cannot be completely removed. Consequently, most neurosurgeons now recommend subtotal (nonradical) tumor resections for critically located meningiomas as a method to reduce symptomatic mass effect at less risk than a complete tumor resection. Nevertheless, even when a meningioma has been completely removed, the tumor recurrence rates may be as high as 15% at 5 years. For patients with benign meningiomas (World Health Organization [WHO] grade I) having tumor recurrence or progression, external beam radiation therapy (EBRT) has been used for many years as a postoperative adjunct to provide tumor growth control, and also for patients with atypical (WHO grade II) or malignant (WHO grade III) meningiomas. Numerous studies have documented that postoperative EBRT decreases tumor recurrence and improves survival for patients after incomplete meningioma resection. Despite improving progression-free survival (PFS) for meningioma patients, EBRT requires 5 to 6 weeks and can result in cognitive decline, radiation-induced neoplasms, or pituitary insufficiency.
As an alternative to surgical resection or EBRT, stereotactic radiosurgery (SRS) has been used for more than 30 years for patients with intracranial meningiomas. In this article, the tumor control and complication rates for patients with intracranial meningiomas having single-fraction SRS at the authors’ center from 1990 until 2008 are discussed.
Indications and technique
The treatment options for patients with intracranial meningiomas include observation with serial imaging, microsurgical resection, EBRT, and SRS. When used appropriately, each modality is important in the management of meningioma patients, and it is not uncommon that a combination of these approaches is needed to achieve tumor control. Factors that are considered in deciding the appropriate treatment include tumor size, tumor location, prior surgery, tumor grade, and patient preference.
Patients with large tumors and symptomatic mass effect are generally considered poor candidates for SRS and surgical resection is performed whenever feasible. Conversely, patients diagnosed with small tumors, especially those patients with minimal deficits, can be considered for observation with serial imaging. Oya and colleagues from the Cleveland Clinic reported 244 patients (277 tumors) who were managed conservatively (mean follow-up, 3.8 years) for their intracranial meningioma. Of note, when volumetric analysis was performed, 114 of 154 tumors (74%) showed tumor enlargement. Factors associated with tumor growth included age ≤60 years, lack of calcification, hyperintensity on T2-weighted magnetic resonance imaging (MRI), tumor size greater than 25 mm, and adjacent edema. Hashimoto and colleagues performed volumetric analysis on 113 patients with incidentally discovered meningiomas. During a mean follow-up period of 46.9 months, 71 tumors (63%) showed a volume increase ≥15%. Tumors located at the skull base grew less frequently (40% vs 75%) and had a longer doubling time when compared with non-skull-base meningiomas (161 months vs 112 months). However, the follow-up period in these studies (approximately 4 years) is too short to conclude that observation alone will be effective for most meningioma patients whose life expectancy when diagnosed is often 20 to 30 years.
If resection is performed and complete tumor removal is not possible, a decision must be made postoperatively either to follow patients with serial MRI or to proceed directly to some form of radiation treatment. Recent studies have shown high rates of tumor progression within 5 to 15 years of subtotal benign meningioma surgery. Therefore, it is likely that most patients in their 50s and 60s with WHO grade I meningiomas and definable tumor remnants on postoperative MRI will show tumor growth postoperatively. Patients with a WHO grade II meningioma and residual tumor should be evaluated for either EBRT or SRS. Patients with residual tumor that is more diffuse are typically best suited for EBRT, whereas patients with more nodular tumor remnants can be managed well with SRS. Patients with WHO grade III meningiomas should undergo postoperative EBRT, with SRS being used primarily as a salvage therapy if the patient has progressive tumor enlargement after EBRT.
Radiosurgery at the Mayo Clinic (Rochester, MN) is performed with the Leksell Gamma Knife (Elekta Instruments, Norcross, GA). Dose planning is primarily performed using stereotactic MRI. In recent years, stereotactic CT has been used in addition to MRI for patients with skull-base meningiomas. Modern SRS software facilitates the creation of conformal dose plans that minimize the radiation exposure to adjacent normal structures ( Fig. 1 ). Dose prescription must take into account the tumor size, location, histology, and history of prior radiation therapy. Tumor margin doses of 12 to 15 Gy are typically prescribed for patients with presumed or documented WHO grade I meningiomas. Higher radiation doses are generally given to patients with WHO grade II or III meningiomas if they have not received prior EBRT and the tumor volume is less than 10 cm 3 . The radiation dose to the optic apparatus must be considered in patients with tumors in the parasellar region. Doses of 10 to 12 Gy can be given safely to small segments (2–4 mm 3 ) of the optic nerve and chiasm in a single fraction. Table 1 outlines the type and number of single fraction meningioma SRS cases performed at the Mayo Clinic from 1990 to 2008.
| Tumor Type | No. of Patients (%) |
|---|---|
| Presumed | 256 (42.5%) |
| WHO Grade I | 225 (37.4%) |
| WHO Grade II | 39 (6.5%) |
| WHO Grade III | 15 (2.5%) |
| Radiation-induced | 28 (4.7%) |
| Multiple meningiomas | 23 (3.8%) |
| Neurofibromatosis type II | 16 (2.7%) |
Related posts:
Stereotactic Radiosurgery of Pituitary Adenomas
Stereotactic Radiosurgery of Intracranial Cavernous Malformations
Radiosurgery for Vestibular Schwannomas
Stereotactic Radiosurgery of Intracranial Dural Arteriovenous Fistulas
Stereotactic Radiosurgery for Brain Metastases
Stereotactic Radiosurgery for Intracranial Gliomas
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
