The mastoid emissary vein: an anatomic study with magnetic resonance imaging

The mastoid emissary vein (MEV) is a small venous channel connecting the intracranial and extracranial venous systems. Most current knowledge about the MEV has been obtained through cadaver studies. This study aimed to explore the MEV in vivo, using magnetic resonance imaging (MRI). Ninety-six patients were enrolled in this study. The initial examinations used the conventional MRI sequences; contrast examinations were performed using thin-sliced sections. The MEVs were identified bilaterally in 59.3 % of the 96 patients and unilaterally in 29.2 %. The original site, size, and intraosseous course of the MEVs were highly variable. On coronal images, the MEVs originated from a variable height on the posterior wall of the sigmoid sinus, most frequently from the lower third of the wall. Intraosseous MEV courses were classified as straight, curved, or tortuous, with the straight type occurring most frequently. The MEVs were dominant on the right side in 51.8 % of cases and on the left side in 24.7 % of cases. Two patients had two MEVs on the same side. Furthermore, on eight sides (5.6 %), the diploic venous channel was found to communicate with the MEV. The MEV is a structure with diverse morphologies and right-sided dominancy. MEVs should be evaluated before performing surgical and endovascular procedures around the suboccipital region.