A Systematic Review With Meta-analysis of the Mastoid Emissary Foramen: Implications for Posterior Cranial Fossa Surgery

INTRODUCTION: The mastoid emissary foramen (MEF), transmitting the mastoid emissary vein, is a key anatomical structure encountered during posterior cranial fossa and cerebellopontine angle approaches. Injury to this variable venous pathway may result in significant hemorrhage. However, published data regarding the prevalence and morphology of the MEF remain inconsistent. METHODS: A systematic review with meta-analysis was conducted according to PRISMA 2020 and Evidence-based Anatomy guidelines. Four databases were searched for osteological and imaging studies reporting MEF prevalence or morphometry were included. Pooled prevalence and morphometric estimates were calculated using random-effects models. RESULTS: Twenty-one studies comprising 8689 skull sides were included. The pooled prevalence of the MEF was 74% (95% CI: 65.16-82.03), with absence in 26%. A single MEF was most common (53%), while multiple MEFs were present in 16% of cases. Two, three, and four MEFs were observed in 12%, 4%, and 0.6% of cases, respectively. Nationality influenced the prevalence of multiple MEFs, whereas laterality and study type did not. The pooled mean diameter of the MEF was 2 mm (95% CI: 1.55-3.14). CONCLUSIONS: The MEF is a common but highly variable anatomical structure. Awareness of its prevalence and morphology is essential for neurosurgical planning, emphasizing the importance of high-resolution preoperative imaging to minimize vascular complications during posterior cranial fossa approaches.