Prevalence of the Sphenoidal Emissary Foramen in a Chilean Osteological Sample: Anatomical and Surgical Implications.

Background: The sphenoidal emissary foramen (SEF) is an inconstant foramen of the sphenoid bone that facilitates venous communication between the pterygoid venous plexus and the cavernous sinus. Understanding its prevalence and laterality is crucial to preventing vascular injury during skull base procedures. Methods: A cross-sectional observational study was conducted on 133 adult Chilean dried skulls. Each specimen was examined both internally and externally to record SEF presence and laterality. Three independent observers performed the assessments under direct lighting, achieving excellent interobserver agreement (κ = 0.87, 95% CI = 0.81-0.92). Descriptive statistics, Chi-square tests, and Cramer's V coefficients were calculated to evaluate side dominance and effect size at a significance level of p < 0.05. Results: The SEF was present in 40.17%. Bilateral foramina were observed in 26.79%, and unilateral SEF in 13.38%. Left-sided SEF (9.12%) was more common than right-sided SEF (4.26%), showing a significant difference (p = 0.03; Cramer's V = 0.19, 95% CI = 0.02-0.33). This mild but significant left-sided prevalence indicates slight directional asymmetry rather than functional lateralization. Conclusions: The Chilean prevalence of the SEF lies within the mid-range of international data and closely aligns with Brazilian osteological reports. Although a minor left-sided predominance was observed, the effect size was weak (Cramer's V = 0.19), reinforcing the interpretation of the SEF as a normal morphological variability rather than a true anatomical variant. Precise preoperative identification of the SEF is crucial to reduce the risk of venous injury and avoid unintentional penetration.