Anatomy of the mastoid emissary vein and venous system of the posterior neck region: neurosurgical implications.

Objective: The superficial venous system of the posterior neck (suboccipital venous plexus) is a potential source of complications from bleeding and air embolism. Because there is little information available about this in the literature, an anatomic study of the superficial posterior neck venous system and a morphometric analysis of the mastoid emissary vein (MEV) complex were undertaken. Both surgical and endovascular implications were considered.

Methods: The posterior craniocervical regions of 15 silicon-injected human cadaveric specimens were dissected. The patterns and variances of venous anatomy were observed. Distances between fixed bony landmarks were measured with a caliper.

Results: The suboccipital venous plexus, which forms a complex venous network located between the posterior muscular layers of the neck, drains to the anterior vertebral vein and deep cervical vein. The MEV connects this plexus to the sigmoid sinus. Its average diameter was 2.15 mm, and it was located a mean of 21.14 mm from the asterion and a mean of 33.65 mm from the mastoid tip. However, the size of the MEV complex varied considerably.

Conclusion: The suboccipital venous plexus in the posterior neck region may be very large. The size of the veins in the plexus varies, but the drainage pattern remains consistent. The plexus is a potential source of intense bleeding and air embolism during posterior fossa approaches. The risks are greatest for lateral surgical approaches, as a result of the anatomic position of the venous system. The described measurements can be used to approach the MEV in endovascular procedures that involve the sigmoid sinus.