Abstract

 

Burr-hole (BH) craniotomy is a surgical procedure that makes a small hole in the skull for cerebrospinal fluid (CSF) drainage or evacuation of blood. Several computational studies using human brain models suggested that the BH filled with CSF after brain surgery may interfere spatial distribution of the electric field (E-field). However, few studies validated computational models incorporating clinical brain MRI images from patients. Here, we examined the E-field strength in target areas in the presence of the BH. Realistic head mesh models were constructed from MR images of three patients. BH was located in the frontal bone in all patients. To characterize the BH effect during tDCS, we labeled a BH filled with (BH-CSF) and without CSF (BH-nCSF). We simulated a tDCS using a pair of 5x5 cm rectangular electrodes at 2 mA and evaluated the E-field strength, E(|V/m|). We considered three electrode configurations (F3-FP2, FP1-F4, and F3-F4: Anode-Cathode), and two target areas (DLPFC and the cortical region beneath the BH). The average E in DLPFC by all three montages was significantly greater (p<0.0391) in BH-CSF (0.337±0.194) in comparison to BH-nCSF (0.186±0.0275). A similar trend was observed in the cortical surface beneath the BH, where BH-CSF (0.634±0.298) was significantly greater (p<0.0078) than BH-nCSF (0.237±0.0280). A Wilcoxon signed-rank test was used for the statistical analysis. Our preliminary results indicated that the BH effect can vary significantly if the position of the BH is closer to the target areas. Specifically, the high conductivity of CSF in BH appeared to draw a greater E-field in the cortical areas beneath the BH, which can manipulate the efficacy of tDCS. Together, our study may suggest that BH conditions including the position and electrical conductivity of tissue filling the BH need to be considered to avoid unfavorable effects of tDCS.