VENOUS DRAINAGE The venous drainage of the posterior fossa can be divided into three systems: the Galenic system, anterior petrosal system, and posterior (or tentorial) system. Galenic System
The Galenic system includes the precentral cerebellar vein, the superior vermian vein, the anterior pontomesencephalic vein, and the posterior and lateral mesencephalic veins. The precentral cerebellar vein is located in the midline in the fissure between the lingula and the central lobule of the vermis. It is formed by the union of veins from the brachium pontis and vermis. It sits posterior to the collicular plate and precentral lobule of the vermis to enter the vein of Galen. It is an important landmark during supracerebellar approaches to the pineal and tectal plate region. The superior vermian vein curves along the anterior surface of the culmen and receives tributaries from the vermis. It also enters the vein of Galen, either with or just adjacent to the precentral cerebellar vein. The posterior mesencephalic vein originates from the outer aspect of the cerebral peduncle and curves around the brain stem in the ambient cistern. Often, it is adjacent to the basal vein of Rosenthal. One of the main tributaries to the posterior mesencephalic vein is the lateral mesencephalic vein, which is an important landmark for identifying the junction of the tegmentum and the cerebral peduncle. The anterior pontomesencephalic vein is a complex of small veins that runs along the ventral and rostral surfaces of the pons and mesencephalon. This vein curves along the interpeduncular fossa below or
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