Microsurgical anatomy of the lateral mesencephalic vein and its meaning for the deep venous outflow of the brain.

The cerebral venous outflow consists of the superficial system and the deep draining system. The deep one drains the areas of the great vein of Galen, the two basal veins of Rosenthal, and their tributaries. Simultaneous obstruction of these veins can effect great harm. In the case of obstruction of the vein of Galen, the basal vein can ensure the venous outflow. Therefore, attention should be paid to anastomoses between the basal vein and the infratentorial venous system. The lateral mesencephalic vein (LMV) is the most important anastomosis between the supra- and infratentorial system linking the basal vein to the superior petrosal sinus. Since microanatomical studies concerning this vein have received less attention the aim of the present study was to visualize the course of this vein, its junction with the basal vein, its tributaries and its relationship with neural structures. Fifty-two cadaveric hemispheres were examined under the operating microscope. The LMV could be identified in all cases, with a mean diameter of 1.07 mm. Thorough understanding of the microanatomy of the LMV is crucial to avoid brain damage due to venous infarction during surgery, and its preservation could ensure deep venous outflow in the case of obstruction of the vein of Galen.