T he brainstem forms the central axis of the brain and comprises the midbrain, pons, and medulla oblongata; it occupies the anterior portion of the cranial posterior fossa (Fig. 1). It is composed of neurons aggregated into nuclei and nerve fibers grouped into bundles called tracts, fasciculi, or lemnisci. These elements of the internal structure may be related to prominences or depressions on the surface, which must be identified by the surgeon. The brainstem is basically composed of 4 types of structures: 1) ascending and descending pathways that connect the spinal cord with the prosencephalon; 2) reflex centers associated with control of breathing, the cardiovascular system, and also consciousness, along the reticular formation; 3) most of the nuclei of the cranial nerves (from CN III to XII); and 4) cerebellar peduncles. 23,36,41,43,49 Brainstem surgery remains a challenge for the neurosurgeon. Recent improvements in neuroimaging, microsurgical techniques, and electrophysiological monitoring, in association with detailed knowledge of regional and functional anatomy, have allowed surgical procedures at this region to become safer and more likely to be successful. To plan the most appropriate approaches, to choose the safest entry zones, and to minimize possible surgical complications, 14,41 it is important for the neurosurgeon to keep in mind both the surface anatomy and the internal architecture of the brainstem. obJective Brainstem surgery remains a challenge for the neurosurgeon despite recent improvements in neuroimaging, microsurgical techniques, and electrophysiological monitoring. A detailed knowledge of the microsurgical anatomy of the brainstem surface and its internal architecture is mandatory to plan appropriate approaches to the brainstem, to choose the safest point of entry, and to avoid potential surgical complications. methods An extensive review of the literature was performed regarding the brainstem surgical approaches, and their correlations with the pertinent anatomy were studied and illustrated through dissection of human brainstems properly fixed with 10% formalin. The specimens were dissected using the fiber dissection technique, under ×6 to ×40 magnification. 3D stereoscopic photographs were obtained (anaglyphic 3D) for better illustration of this study. results The main surgical landmarks and their relationship with the cerebellum and vascular structures were identified on the surface of the brainstem. The arrangements of the white matter (ascending and descending pathways as well as the cerebellar peduncles) were demonstrated on each part of the brainstem (midbrain, pons, and medulla oblongata), with emphasis on their relationships with the surface. The gray matter, constituted mainly by nuclei of the cranial nerves, was also studied and illustrated. coNclusioNs The objective of this article is to review the microsurgical anatomy and the surgical approaches pertinent to the brainstem, providing a framework of its external and internal architecture to guide the neurosurgeon during its ...
