Foramen magnum meningioma: Series of 20 cases. Complications, risk factors for relapse, and follow-up

INTRODUCTION: Meningiomas account for 2.2% to 2.5% of all cerebral tumors, of which only 2% are located in the foramen magnum. Foramen magnum meningiomas (FMMs) are commonly found in women, with a mean age at onset of 52 years old. They generally behave more aggressively than other meningiomas. MATERIALS AND METHODS: We performed epidemiological, anatomical and surgical analyses of 20 patients diagnosed with FMMs who underwent surgical treatment from 1999 to 2019 at Santa Paula Hospital in Sao Paulo. This case series was compared with previously published ones to better understand this relatively rare disease. RESULTS: Twenty patients were included, with a mean follow-up of 110 months. Their mean age was 37.8 years old. The mean preoperative Karnofsky performance status scale (KPS) was 84%. We found a female (65%) and left hemisphere predominance (50%). Involvement of both hemispheres was found in 25% of patients. FMM locations were anterior, anterolateral, lateral and posterior, in 45%, 35%, 10%, and 10%, respectively. Simpson resection grades I, II, and III were achieved in 25%, 60%, and 15% of cases, respectively. Mean postoperative KPS was 79%. Three patients with anterior and bilateral located meningiomas had a worse postoperative KPS in comparison to the preoperative one. CONCLUSION: Anterior and bilateral FMMs seem to be related to a worse prognosis. A gross total resection can reduce the recurrence rates. The KPS is worse in patients with recurrence.