Clinical anatomy of the mastoid and occipital emissary veins in a large series

Abstract

Detailed descriptions of the mastoid emissary veins (MEVs) and the foramina through which they travel are lacking in the literature. Therefore, the aim of our study was to explore and delineate the morphology, topography and morphometry of the MEV, mastoid foramen (MF) and occipital foramen (OF). One hundred cadaver heads and 100 dried human skulls were grossly examined The MF and OF varied from being absent to having as many as four small openings, each transmitting an emissary vein. The overall prevalence of MEV was 98% on the right and 72% on the left. The overall prevalence of OF was 7% on the right and 4% on the left. The mean length of the MEV from its point of origin to its point of termination was found to be 7.2 cm with a range of 3.8-11.8 cm. The mean diameter of the MEV at the mastoid emissary foramen was 3.5 mm with a range of 1.1-5.6 mm. In the majority of the cadavers (85%) it was observed that mastoid and occipital emissary veins formed a confluent venous system, while in the remaining 15%, they remained as single vessels. The MEV may be a significant source of bleeding during surgery of the skull base or middle ear, particularly during retrosigmoid and far-lateral approaches and detailed anatomical knowledge may help to prevent these complications. Endovascular treatment of dural arteriovenous fistulas is often extremely difficult due to limited access, however, the use of the MEV represents a unique and potentially valuable technique for accessing an isolated or inaccessible transverse or sigmoid sinus system.