RESUMO

Most of the motor mapping procedures using navigated transcranial magnetic stimulation (nTMS) follow the conventional somatotopic organization of the primary motor cortex (M1) by assessing the representation of a particular target muscle, disregarding the possible coactivation of synergistic muscles. In turn, multiple reports describe a functional organization of the M1 with an overlapping among motor representations acting together to execute movements. In this context, the overlap degree among cortical representations of synergistic hand and forearm muscles remains an open question. This study aimed to evaluate the muscle coactivation and representation overlapping common to the grasping movement and its dependence on the stimulation parameters. The nTMS motor maps were obtained from one carpal muscle and two intrinsic hand muscles during rest. We quantified the overlapping motor maps in size (area and volume overlap degree) and topography (similarity and centroid Euclidean distance) parameters. We demonstrated that these muscle representations are highly overlapped and similar in shape. The overlap degrees involving the forearm muscle were significantly higher than only among the intrinsic hand muscles. Moreover, the stimulation intensity had a stronger effect on the size compared to the topography parameters. Our study contributes to a more detailed cortical motor representation towards a synergistic, functional arrangement of M1. Understanding the muscle group coactivation may provide more accurate motor maps when delineating the eloquent brain tissue during pre-surgical planning.

Assuntos

Córtex Motor , Mapeamento Encefálico/métodos , Potencial Evocado Motor/fisiologia , Antebraço/fisiologia , Mãos , Humanos , Córtex Motor/fisiologia , Músculo Esquelético/fisiologia , Estimulação Magnética Transcraniana/métodos

RESUMO

BACKGROUND: Navigated transcranial magnetic stimulation (nTMS) is a well establish a noninvasive method for preoperative brain motor mapping. We commonly use magnetic resonance imaging (MRI) to supply the nTMS system. In some cases, MRI is not possible or available, and the use of computed tomography (CT) is necessary. We present the first report describing the association of CT and nTMS motor mapping for brain lesion resection. CASE DESCRIPTION: CT imaging of a 59-year-old man suffering from acquired immune deficiency syndrome for 17 years, presenting with seizure and right hemiparesis, revealed a small single hypodense ring-enhancing lesion in the left central sulci suggesting cerebral toxoplasmosis. After 3 weeks of neurotoxoplasmosis treatment, due to four consecutive tonic-clonic seizures, a new CT scan was performed and showed no lesion changes. MRI was in maintenance at that time. Infectious diseases department suggested a brain lesion biopsy. Due to lesion's location, we decided to perform a presurgical nTMS motor mapping. After a small craniotomy, we could precisely locate and safely totally remove the lesion. The pathology report revealed a high suspicious toxoplasmosis pattern. The patient was discharged after 2 days and continued toxoplasmosis treatment. After 6 months follow-up, he showed no signs of any procedure-related deficits or radiological recurrence. CONCLUSION: We report the feasibility and applicability of nTMS motor mapping using CT scan as an image source. It gives neurosurgeons another possibility to perform motor mapping for brain lesion removal, especially when MRI is not available or feasible.

RESUMO

OBJECTIVES: To determine whether high-frequency 250-500 Hz monopolar stimulation is effective for mapping cortical and subcortical language structures during brain tumor resection. METHODS: Using high-frequency monopolar stimulation, we mapped the speech areas of 41 awake patients undergoing brain tumor resection in the dominant hemisphere, subject to risk of lesions in the cortical and subcortical speech tracts. Patients were tested for object naming, semantic and other language tasks. RESULTS: Mapping was positive in 22 out of 41 patients. Nine patients presented clinical worsening immediately after surgery. Only one patient did not recover after the 30-day follow-up. Nineteen patients showed negative mapping for language tracts, none of whom exhibited worsening of symptoms at the final evaluation. The applied method showed 89% sensitivity and 56% specificity rates. CONCLUSIONS: The applied method was effective in identifying cortical and subcortical speech areas during the surgical resection of brain tumors. SIGNIFICANCE: Determining whether monopolar high-frequency stimulation is effective for language mapping is important, since it may be very effective in infiltrating tumor areas and nearby edema region.