The electrical conductivity of human cerebrospinal fluid in vivo

Cerebrospinal fluid (CSF) is a clear, highly conductive liquid. Due to its much higher electric conductivity compared to other intracranial tissues, its influence is significant, for example, on volume conductor models, current distribution and heat generation in RF surgery. It has already been shown previously that it is important to include CSF in models to achieve more accurate results. Conductivity values measured in vitro are commonly used in modelling because in vivo values are not available. We have developed a method for taking calibrated in vivo human CSF conductivity measurements with a needle electrode. We used this method to take CSF conductivity measurements from four patients during brain surgeries that were conducted to remove tumours. The patients were selected so that the surgical path went through a ventricle to make sure that there was enough CSF volume to take the measurements. Two of the patients had meningiomas and the other two had gliomas. Measurements taken from clear CSF with our method resulted in conductivity values of 1.79–1.81 S/m. Impurities such as blood or the presence of cystic brain tumour decreased the measured electrical conductivity of CSF. Our results support the findings that the previously suggested conductivity value of 1.79 S/m for human CSF at 37 °C taken from in vitro measurements is applicable for modelling purposes.