Brainstem Anatomy: A Study on the Basis of the Pattern of Fiber Organization

A focused dissection of the brainstem was performed to study the various fiber bundles and gray matter nuclei of the brainstem and to decipher the intricate anatomy. Ten formalin-fixed cadaveric human brains were procured. The fiber dissection techniques described by Klingler were then adopted to study the anatomy. The primary dissection tools used were thin handmade wooden spatulas and fine jeweler's forceps. The fibers were dissected layer by layer with the use of magnification. The brainstem dissection was performed from the dorsal, ventral, and lateral aspects to provide a 3-dimensional perspective of the internal architecture. We have presented a novel classification of the brainstem white matter in accordance with the internal organization. The fiber tracts of the brainstem can be divided into short projection fibers, long projection fibers, traversing fibers, and association fibers. From our dissection findings, we divided these white fibers of the brainstem into 3 zones from laterally to medially. The first or outermost zone consists of short projection fibers connecting the brainstem to the cerebellum and adjacent thalamic nuclei. The second zone or the middle zone lies medial to the first zone and consists of traversing and long projection fibers. These consist of both ascending and descending fibers. The third zone or the innermost zone consists of the brainstem association fibers. This division of the fiber bundles into zones will help neurosurgeons in understanding the course and anatomy of the fibers, which can be cumbersome to remember when only studying the sectional anatomy of the brainstem.