Brainstem Lesion Surgery : Surgical Approaches and Indication

Abstract

  This is a review paper of a variety of surgical techniques and approaches to the brainstem. Brainstem surgery is indicated to remove lesions, such as cavernous malformations, gliomas, hemangioblastomas, and so on. As a rule, an incision should be made on the brainstem at the point where the lesion is the closest to the brainstem surface. To simulate the entry route, the “two-point method” has been proposed. Although, it is necessary to understand the anatomy of the important structures in the brainstem, simulation with preoperative imaging studies is also useful to understand deviated structures presented by the lesions. In order to minimize the damage due to surgery, intraoperative monitoring is very useful, such as motor evoked potential (MEP), auditory brainstem response (ABR), somatosensory evoked potential (SEP), electrocardiogram (EEG), and electrical stimulation of the facial nerve.

  A typical approach to the dorsal midbrain is the occipital transtentorial approach (OTA). To approach the midbrain from the ventral side, the orbitozygomatic approach or trans-lamina terminalis approach is useful. The trans-fourth ventricle approach is used to approach the pons or medulla oblongata from behind. To widely open the fourth ventricle, trans-cerebellomedullary fissure (CMF) approach is useful. As for an antero-lateral approach to the pons and medulla oblongata, the subtemporal approach, anterior petrosal approach, and far lateral (transcondylar) approach are all approaches of choice in avoiding injuries to the pyramidal tract.