Surgical Anatomy of the Posterior Part of the Foramen Magnum and the Posterior Paramedian Approaches

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The atlanto-occipital joint lies in the lateral portion of the foramen magnum, which along with the vertebral artery (VA) forms obstacles to approaches that pass through the lateral foramen magnum. Because the sigmoid sinus and jugular foramen are situated in the lateral part of the foramen magnum, lesions of foramen magnum must be approached from either the anterior or posterior side. The transoral approach, which is an approach from the anterior side, is rarely utilized. In contrast, the posterior approaches are often utilized and are divided into three groups: posterior midline, posterior paramedian, and lateral foramen magnum approaches [1, 2, 4, 6, 13, 16, 19–21]. The posterior paramedian is further subdivided into the intradural, epidural, and combined approaches. In this chapter, we explain the posterior paramedian intradural and epidural approaches for lesions in the anterior or anterolateral foramen magnum. In addition, we explain the surgical anatomy relevant to these approaches, including the bony structures, surrounding nuchal muscles, the VA as it penetrates the dura mater, and venous and neural structures near the foramen magnum.