Introduction: Meningiomas are the most common benign extramedullary lesions of the foramen magnum. Given their location, foramen magnum meningiomas (FMM) can cause significant morbidity, and complete microsurgical resection can be challenging. Anterior and anterolateral FMM carry greater risks with surgery, but comprise the majority of these lesions. Stereotactic radiosurgery (SRS) has been reported for FMM in small case series. To more clearly define the outcomes of SRS and to delineate a rationale management paradigm for these lesions, we analyzed safety and efficacy in an international, multicenter trial.

Methods: Seven medical centers participating in the International Gamma Knife Research Foundation (IGKRF) provided data for this retrospective, cohort study. Patients treated with Gamma Knife SRS, with clinical and radiologic follow-up greater than 6 months were included.

Results: Fifty-seven patients met inclusion criteria for the study. Thirty-two percent had undergone prior microsurgical resection. Patients most frequently presented with cranial neuropathy (39%), headache (35%), numbness (32%), and ataxia (30%). Median pre-SRS volume was 2.9 cm3. Median SRS margin dose was 12.5 Gy (range 10-16 Gy). At last follow-up after SRS, 49% of tumors were stable, 44% had regressed, and 7% had progressed. Progression free-survival at 5 and 10 years was 97 and 92%, respectively. Greater margin dose was associated with a significantly increased likelihood of tumor regression with 53% of tumors treated with > 12 Gy regressing. Fifty-two percent of symptomatic patients noted some clinical improvement. Adverse radiation effects were limited to hearing loss and numbness in one patient (2%).

Conclusions: SRS for FMM frequently results in tumor control or regression, as well as symptom improvement. Margin doses > 12 Gy were associated with increased rates of tumor regression. SRS was generally safe and well-tolerated. Given this risk-benefit profile, SRS may be particularly useful in the management of small- to moderate-volume anterior and anterolateral FMM.

Patient Care: This is the largest series of patients with foramen magnum meningiomas treated with SRS. It helps define the outcomes of treatment in these patients and the role of SRS in a rationale management paradigm. Furthermore, it identifies a margin dose of > 12 Gy as an optimal treatment dose.

Learning Objectives: 1) Understand the efficacy of SRS for foramen magnum meningiomas 2) Understand the safety profile of SRS for foramen magnum meningiomas 3) Discuss management options for foramen magnum meningiomas

References: 1) George B, Lot G, Boissonnet H: Meningiomas of the Foramen Magnum: A Series of 40 Cases. Surg Neurol 47:371–9, 1997 2) Zenonos G, Kondziolka D, Flickinger JC, Gardner P, Lunsford LD: Gamma Knife surgery in the treatment paradigm for foramen magnum meningiomas. J Neurosurg 117:864–873, 2012