Brain Stem Anatomy and Surgical Approaches

Abstract The brain stem is one of the most important neural structures in the central nervous system. It is about 7–10 cm long and it can reach up to 4 cm in an axial direction at its widest portion. Its anterior boundary is the clivus; laterally it is limited by the bony portion of the temporal bone, superiorly by the diencephalon, posteriorly by the cerebellum, and inferiorly it continues on as the spinal medulla in close juxtaposition to the foramen magnum. Due to its complex anatomy, it is crucial to understand not only its external structure but also its inner composition, which is formed by the main pathways that run upward and downward, its nuclear complexes, internal and external connections, cortical connections, and their medullary projections. Only with a thorough knowledge of brain stem anatomy can we find ways to safely access lesions in the brain stem since many of these lesions distort the anatomy in the brain stem that consists of densely packed, highly critical neural nuclei and white matter tracts. In this chapter, we will analyze the internal and external brain stem anatomy followed by providing some practical anatomical tips related to surgical approaches to the brain stem.