The Anatomy of the Mastoid Emissary Vein and the Venous System of the Posterior Neck Region: Neurosurgical Implications

Introduction: The venous tributaries at and around the craniocervical region are a potential source of complications from bleeding and air embolism. However, anatomic information on the venous connections is lacking in the literature. This combined anatomic and morphometric study was undertaken to analyze the mastoid emissary vein (MEV) complex which is routinely encountered in neurovascular surgery or surgery of the craniovertebral junction. Methods: Human cadaveric specimens previously injected with colored silicone were dissected to trace extra- and intracranial vessels, particularly in the suboccipital and mastoid regions. Measurements were taken with a caliper in relation to strategic bony landmarks. Results: An extensive tributary system and engorgement of veins formed a complex venous network located between the posterior neck musculature. The MEV, averaging 1.83 mm in diameter (0.8–2.2 mm), is located 21.28 mm (S.D. ± 3.98) from the asterion and 29.75 mm (S.D. ± 3.64) from the mastoid tip. Conclusions: The MEV may in fact be a considerable structure—its size can be on the order of a cranial sinus. The cavernous venous system in the posterior neck region could be a source of bleeding and air embolism during neurosurgical approaches involving the sigmoid sinus. The risks are greater in the lateral approaches due to the anatomical position of the venous system. The measurements described here show the MEV is easily approachable in endovascular procedures involving the sigmoid sinus.