Comparative Efficacy of Navigated Transcranial Magnetic Stimulation vs. Direct Electrical Stimulation for Motor Cortex Mapping in Brain Tumor Patients: Impact of Histological Grading and Edema

Introduction: Transcranial magnetic stimulation (TMS) represents a distinctive technique for non-invasive brain stimulation. Recent advancements in image processing have enabled the enhancement of TMS by integrating magnetic resonance imaging (MRI) modalities with TMS via a neuronavigation system. This study aims to compare the efficacy of navigated TMS for motor cortex mapping with surgical mapping using direct electrical stimulation (DES), focusing on the influence of histological grading and peritumoral edema in patients with brain tumors.

Methods: This study included 30 neurosurgical procedures for tumors classified as glioblastoma multiforme (n=9, 30%), low-grade glioblastoma (n=8, 26.7%), meningioma (n=7, 23.3%), or brain metastasis (n=6, 20%), all located in or adjacent to the precentral gyrus. Peritumoral edema was present in 22 patients (73.3%). DES points were compared with TMS responses based on the original distances of vectorial modules.

Results: A notable similarity was observed between the mapping points obtained from TMS and DES. No statistically significant differences were found in the coordinate modules comparing the four histological types across both methods (X, p=0.527; Y, p=0.365; Z, p=0.078). Although a smaller distance between vectorial modules was noted in low-malignancy tumors, this difference was not statistically significant (p=0.680). Patients exhibiting deficits demonstrated high accuracy in both methods. Additionally, the presence of peritumoral edema reduced the accuracy of TMS mapping (p=0.038). The resting motor threshold was higher in patients with greater peritumoral edema intensity in both methods, although this difference was not statistically significant (p=0.0714).

Conclusion : In summary, TMS demonstrated reliable and precise application in brain mapping, yielding improved results across three spatial planes for various histological types of brain tumors compared to DES. The presence of peritumoral edema significantly influenced brain mapping outcomes. These findings indicate good accuracy for TMS in preoperative functional mapping for motor cortex tumor surgery.