Brain stem mapping: neurophysiological localization of motor nuclei on the floor of the fourth ventricle

Neurosurgery. 1995 Nov;37(5):922-9; discussion 929-30. doi: 10.1227/00006123-199511000-00011.


We have improved upon a brain stem mapping technique that can be used to locate cranial motor nuclei on the floor of the fourth ventricle. This technique helped to intraoperatively locate the facial colliculus and the motor nuclei of cranial nerves IX/X and XII in 14 patients undergoing removal of brain stem tumors. The motor nuclei of these cranial nerves are usually located relative to specific anatomic landmarks on the ventricular floor. These landmarks were not evident in most patients studied because of the distorting effects of the tumor. Different points of the floor of the fourth ventricle were electrically stimulated while electromyographic responses were recorded with electrodes inserted in the orbicularis oculi and orbicularis oris muscles, the lateral posterior pharyngeal wall, and the intrinsic muscles of tongue. Mapping was performed before and after tumor resection. The technique was found to be useful for locating cranial motor nuclei before tumor resection. It enabled surgeons to avoid damaging the nuclei when entering the brain stem. This technique, however, has certain limitations. Because this is a mapping technique, not a monitoring technique, continuous monitoring during tumor resection was unavailable. Also, the presence of a muscle response after tumor resection did not always indicate preservation of immediate postoperative function (7 days after surgery) because damage to the corticobulbar tract and/or the underlying neural circuitry was not detectable by mapping. Further research is needed to determine the point of stimulation in the functional motor circuitry and the relationship between intraoperative recordings and postoperative function in the long term.

MeSH terms

  • Adolescent
  • Adult
  • Brain Mapping / instrumentation*
  • Brain Neoplasms / physiopathology*
  • Brain Neoplasms / surgery
  • Brain Stem / physiopathology*
  • Brain Stem / surgery
  • Cerebral Ventricles / physiopathology*
  • Cerebral Ventricles / surgery
  • Child
  • Child, Preschool
  • Cranial Nerves / physiopathology*
  • Cranial Nerves / surgery
  • Electroencephalography / instrumentation
  • Electromyography / instrumentation
  • Facial Muscles / innervation
  • Female
  • Humans
  • Infant
  • Male
  • Monitoring, Intraoperative / instrumentation
  • Motor Neurons / physiology*
  • Neurologic Examination
  • Postoperative Complications / physiopathology