Neuromonitoring

The goal of neuromonitoring is to measure the function of eloquent brain areas during resection of tumors even if the patient is in general anaesthesia. In most cases the region of interest is the brain area responsible for movement of the opposite half of the body, but other areas that are responsible e.g. for visual and sensory perception can be monitored as well. With this technique the surgeon is receiving two sorts of information during the course of the operation: 1) functionality of the analyzed brain region and 2) the distance to the region.

Neuromonitoring is based upon electric principles because cells of the nervous system are sending and receiving information with electric potentials. During the operation nervous cells, for instance those responsible for movement, can be stimulated with an electric probe and the resulting activity in the muscles of the body, which are controlled by those cells, can be measured. Like this the functionality of the nervous cells is monitored. To obtain information on the distance to an eloquent brain area the electric current of the stimulating probe can be changed. One milliampere (1mA) is roughly infiltrating the brain tissue for 1mm. During the operation, for instance near the region responsible for movement, the surgeon can measure if he receives activity in the corresponding muscles after applying different strengths of electrical current. If a potential is received with 5 mA we know that the distance to the nervous cells controlling that particular set of muscles is approximately 5mm.

All in all neuromonitoring is working like a compass for eloquent brain areas. Therefore it can help to decide if a resection can be continued safely near eloquent brain areas or if the resection must be stopped. However, it is not a tool to visualize the tumor itself and does not help in “in-eloquent” brain areas, where the output of the nervous cells can not be measured.