Microsurgery of the fourth ventricle: Part 1. Microsurgical anatomy.

Operations on the 4th ventricle offer the potential for injury of the brain stem, cerebellum, cranial nerves, and major cerebellar arteries and veins. Twenty-five cadaver brains were examined using 3x to 25x magnification to define the relationship of these vital structures to the 4th ventricle. The 4th ventricle has a roof, a floor, and two lateral recesses. Most of the cranial nerves arise near the floor, which sits on the pons and medulla. The superior half of the roof, formed by the superior medullary velum, lingula, and cerebellar peduncles, is intimately related to the cerebellomesencephalic fissure, the superior cerebellar arteries, and the vein of the cerebellomesencephalic fissure. The inferior half of the roof, formed by the inferior medullary velum, tela choroidea, nodule, and uvula, is intimately related to the cerebellomedullary fissure, the posterior inferior cerebellar arteries, and the veins of the cerebellomedullary fissure. The lateral recesses and adjoining parts of the roof and floor are intimately related to the cerebellopontine fissures, the anterior inferior cerebellar arteries, and the veins of the cerebellopontine fissure. The cerebellar peduncles converge on and form a major part of the ventricular surface. The hili of the dentate nuclei abut on the superolateral recesses of the ventricle near the superior poles of the tonsils.