Occipital emissary foramina in human skulls: review of literature and proposal of a classification scheme of the occipital venous anastomoses in the posterior cranial fossa

Abstract

Objectives: The present study aims to explain the interesting discrepancy between the occipital emissary foramina and the respective emissary veins in the literature. Majority of the studies report that the foramina have a low and variable frequency, but the emissary veins are reported to be disproportionately present in quite large number of patients in some diagnostic imaging studies. Methods: Seventy-five adult skulls were examined for the presence of occipital foramina. Results: A complete occipital emissary foramen was found only in one skull (1.33%), but a number of other skulls also showed some foramina on the external and internal surfaces of squamous part of the occipital bone. Conclusion: It can be concluded that foramina of another vein which is related to the squamous part of occipital bone, the occipital diploic vein, might be the main reason for the discrepancies present in the literature. The suggested classification scheme of venous anastomoses in the posterior cranial fossa can explain the variable bony foramina observed in skull series.