Objective: Foramen magnum meningiomas (FMMs) represent a considerable neurosurgical challenge given their location and potential morbidity. Stereotactic radiosurgery (SRS) is an established non-invasive treatment modality for various benign and malignant brain tumors. However, reports on the use of single-session or multisession SRS for the management and treatment of FMMs are exceedingly rare, with approximately 100 unique cases described in the literature until now. We report our multicenter treatment experience with SRS utilizing robotic radiosurgery.

Methods: Patients who underwent SRS between 2005 and 2020 as a treatment for a FMM at six different centers were eligible for analysis. All treatments were delivered using the CyberKnife robotic radiosurgery system (Accuray Inc., Sunnyvale, CA, USA). Local tumor (LC) control, symptoms, and adverse events were evaluated clinically and by magnetic resonance imaging.

Results: Sixty-two patients met the inclusion criteria. The median follow-up was 28.9 months. The median prescription dose and isodose line were 14 Gy and 70%, respectively. Single-session SRS accounted for 81% of treatments. The remaining patients received three to five fractions, with doses ranging from 19.5 to 25 Gy. Ten (16%) and thirteen patients (21%) were treated for a tumor recurrence after surgery or underwent adjuvant treatment, respectively. The remaining 39 FMMs (63%) received SRS as their primary treatment. For patients with an upfront surgical resection, histopathological examination revealed 22 World Health Organization grade I tumors with one grade II FMM. The median tumor volume was 2.6 cubic centimeter. Most common pre-SRS deficits included sensory dysfunctions (21%), headaches and neck pain (20%), as well as ataxia and muscle weakness (18%). No local failures were observed throughout the available follow-up, including patients with a follow-up ≥ five years (16 patients), leading to an overall LC of 100%. Tumor volume significantly decreased after treatment, with a median volume reduction of 21% at the last available follow-up (p < 0.01). Most patients either showed stable (47%) or improved (21%) neurological deficits at last follow-up. No high-grade adverse events were observed.

Conclusion: SRS appears to be an effective and safe treatment modality for FMMs. Despite the paucity of available data and previous reports, SRS should be considered for selected patients, especially those with subtotal tumor resections, recurrences, and patients not suitable for surgery.