How far is C3 located from the left pre-auricular point?

The distance from the left preauricular point to C3 is traditionally established as approximately 9 cm. This measurement is part of the standard international 10-20 electrode placement system used in electroencephalography and other neurophysiological monitoring. The preauricular point, located just in front of the ear, serves as a reference point for locating the electrode positions on the scalp.

In this system, C3 is situated on the left side of the head, and by using standardized measurements relative to this reference point, clinicians can accurately place electrodes for monitoring purposes. This consistency in measurements is crucial for ensuring reliable data during procedures that use neurophysiological monitoring, such as those performed by neurophysiologic intraoperative monitoring professionals. Understanding these distances helps in maintaining the integrity and accuracy of electrophysiological assessments in relation to surgical interventions.