Monitoring Posterior Fossa Craniotomies

Abstract

The base of the skull is divided into three cranial fossae: posterior, middle, and anterior (Fig. 14.1). The posterior fossa is the deepest and largest and is enclosed by the occipital bone. Within the posterior fossa are the brainstem and cerebellum. The brainstem—consisting of the midbrain (mesencephalon), pons, and medulla—contains the nuclei of cranial nerves (CN) III–XII and is responsible for vital autonomic nervous system function. The brainstem also contains afferent and efferent fiber tracts that connect the brain with the rest of the body. The cerebellum is responsible for movement, balance, and coordination. Due to the complex anatomy and close proximity of these vital structures to each other, the use of intraoperative neuromonitoring (IOM) during posterior skull base surgery can aid the surgeon in identifying neural structures at risk as well as verifying neural integrity once the decompression is complete. This chapter focuses on surgeries for microvascular decompression (MVD), vestibular schwannoma, and Chiari malformation and the modalities used to preserve the neurological function of cranial nerves and brainstem structures during these types of surgeries.