Purpose Foramen magnum meningiomas (FMMs) are a major surgical challenge, due to relevant surgical morbidity and mortality. The paper aims to review the clinical (symptomatic improvement, complication rate, length of hospital stay) and radiological outcome (completeness of resection) of microsurgical resection of FMMs, and to identify predictors of complications. Methods A multi-institutional retrospective review of prospectively maintained database of FMMs included 51 patients (74.5% females) with a median tumor volume of 8.18 cm3 (range, 1.77–57.9 cm3) and median follow-up of 36 months (range, 0.30–180.0 months). Tumors were resected though suboccipital approach (58.8%) or transcondylar approach (39.3%). Results Gross-total resection (GTR) was achieved in 80.4%, while local tumor control in 98% of cases. Clinical symptoms improved in 34 patients (66.7%) and worsened in 5 (9.8%). The median length of hospital stay was 5 days. Mortality was null. Postoperative complications developed in 15 patients (29.4%), with cerebrospinal fluid leak (7.8%) and lower cranial nerves deficits (7.8%) as the most frequent. Craniospinal location (p = 0.03), location anterior to the dentate ligament (DL) (p = 0.02), involvement of vertebral artery (VA) (p = 0.03) were significantly associated with complication rate. These three elements allow calculating the Foramen Magnum Meningioma Risk Score (FRMMRS), to estimate the risk of post-operative complications. Conclusion Microsurgical resection allows for high GTR rate and local tumor control rate, despite complications in one third of the patients. The FMMRS allows classifying FMMs and estimating the risk of post-operative complications.
