Arterial and neural relations at the posterior and lateral aspects of the medullo-spinal junction.

The authors report the results of a series of 59 microdissections of the region of the foramen magnum. These dissections were made under the strict conditions of a surgical approach using an operating microscope. The major anatomic structures of the medullo-spinal junction are arranged mainly at its lateral aspect. The customary surgical approaches to the posterior cranial fossa give ready access to the cerebello- and latero-medullary cisterns. The description of the neurovascular structures contained therein assumes a particular importance because of the relative frequency of lesions developing at this level. This study deals particularly with the vertebral a. (VA), the inferior posterior cerebellar a. (IPCA), the cranial nn. IX (glossopharyngeal n.), X (vagus n.), XIc and XIs (cranial and spinal accessory n.) and XII (hypoglossal n.). The anatomy of this posterior and lateral region is characterised by the contrast between the relatively uniform course of the VA and the variable course of the IPCA, a true guideline whose very irregular arrangement accounts for the diversity of its relations with the last four cranial nn.