Interdisciplinary Neurosurgery (Dec 2022)
Intraoperative cortical and subcortical stimulation for lesions related to eloquent motor cortex and corticospinal tract in a developing country
Abstract
Objective: Surgery for lesions related to the eloquent motor cortex and the corticospinal tract is challenging. Intraoperative cortical and subcortical stimulation are reliable techniques for motor cortex and corticospinal tract (CST) mapping. Pre-operative functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) are able to provide helpful data for safe surgical planning with both cortical and subcortical lesion resection. The authors combine these imaging techniques with intraoperative stimulation to identify and preserve cortical and subcortical motor tissue. Methods: This is a prospective analysis of 56 patients between May 2020 and June 2021, who underwent lesion resection. Thirty-one patients underwent preoperative DTI, thirteen patients underwent preoperative fMRI and their data were used for a tractography-based neuronavigation system. All patients were operated under general anesthesia. Intraoperative mapping data were collected from operative protocol and neurophysiologist’s notes. The assessment of paresis was done by an independent neurosurgeon and was carried out using the motor strength scale of 0–5 according to the Medical Research Council scale. All patients with new or worsened postoperative motor deficits were followed for 6 months. Results: None of the patients exhibited a seizure during the operation. There were eight cases that experienced immediate motor deficits after surgery. At six months after surgery, only two patients (3.6%) had permanent motor deficits (motor strength scale rating 3 in one case and 4 in the other). The average distance between the lesions and CSTs in the positive subcortical stimulation response group was 3.39 ± 2.19 mm and 8.59 ± 3.27 mm in the negative group. Using a 5 mA stimulation threshold value resulted in a sensitivity of 12.5% and a specificity of 92.7%, corresponding to a negative predictive value of 84.4% and a positive predictive value of 25% for motor function. Conclusions: Intraoperative cortical and subcortical motor mapping in lesion resection resulted in a low ratio of permanent postoperative deficits. Subcortical alert threshold ≤ 5 mA is supposed to be a safe threshold in lesion resection with a high specificity of 92.7% and a negative predictive value of 84.4%.
