Association between the morphological features of the central sulcus and the somatomotory representation: anatomo-functional evaluation of neuroplasticity through nTMS.

Abstract

In recent years navigated transcranial magnetic stimulation (nTMS) has emerged as a useful tool for the preoperative mapping of brain cortical areas surrounding neoplastic tissues allowing for maximal safe tumor resection and minimizing new postoperative permanent neurological deficits. Three patients presenting with an intrinsic brain tumor (one metastasis from mammary carcinoma, one high-grade glioma, and one low-grade glioma) located within or in close relationship to the central sulcus were enrolled for this study. The MRI-based morphological and nTMS mapping of the central sulcus of the intact hemisphere was complemented by the examination of the contralateral region harboring the lesion. The findings were independently compared, in search of evidence of tumor-induced neuroplasticity and/or signs of parenchymal dislocation/infiltration caused by the tumor. An individual description of each mapping session is provided. Significant discrepancies were observed between morphological MRI and functional nTMS mapping in two patients, demonstrating a tumor-induced shift of distinct cortical areas controlling hand and/or facial movements. In the cases of gliomas, a lower MT was detected in the lesioned hemisphere, possibly due to increased electrical excitability caused by the tumor itself. The integration of MRI-based morphological mapping of the central sulcus with the detection of its somatomotor representations through nTMS can assist neurosurgeons when planning the resection of a motor-eloquent tumor, stratifying the risks of secondary neurological deficits. The combination of the two preoperative techniques is able to disclose tumor-induced neural plasticity subsequently guiding a more precise resection.