Microsurgical anatomy of the subtentorial supracerebellar and infracerebellar approach to the trigeminal and facial nerves.

The microsurgical anatomy of the subtentorial supracerebellar approach to the trigeminal nerve and the infracerebellar lateral approach to the facial nerve was examined in five formalin-fixed adult cadavers. Particular attention was directed to the arrangement of the blood vessels within the posterior fossa, especially the superior petrosal vein and its tributaries, the superior cerebellar artery (SCA), the anterior inferior cerebellar artery (AICA) and the posterior inferior cerebellar artery (PICA). The subtentorial supracerebellar approach provides satisfactory exposure of both, the lateral segment of the SCA, which is the most common vessel involved in the neurovascular conflict resulting in trigeminal neuralgia and the y-inverted shaped superior petrosal vein. The latter results more often from the convergence of the pontotrigeminal vein and the vein of the cerebellopontine fissure. The relationship between the AICA, the PICA and the vertebral artery to the facial-vestibulocochlear complex was studied by an infracerebellar lateral approach. The subpial course of the facial nerve, where the vascular compression is usually found which results in hemifacial spasm, was also documented. These two approaches, as well as a historical review of the evolution of these surgical techniques, since the first description by Dandy, are discussed. Copyright 1999 Harcourt Publishers Ltd.