Radical but safe elimination of lesions in central areas of the brain and spine calls for accurate assessment of eloquent neural structures to reduce the risk of a permanent neurological deficit after surgery. Despite marked advances in cortical mapping of sensorimotor functions by neuroradiodiagnostic methods, their application in particular in subcortical mapping and mapping of verbal functions is still inadequate. Individual deviations in the anatomical and functional pattern of sensorimotor and verbal functions affected by a tumour require direct peroperative identification of these functions in cortical as well as subcortical areas. It was found that direct peroperative electrical stimulation of the central nervous system makes possible immediate and safe assessment of important cerebral and spinal regions on the surface as well as at deep sites and also checking of their function. The authors used direct electrical stimulation in a prospective study implemented from January 1996 till July 2000 in 50 supratentorial processes situated in eloquent areas of the brain (precentral 20, postcentral 19, perisylvic 5, extensive fronto-parietal 4, deeply situated 2) and in 4 spinal tumours. The group comprised 28 men and 26 women aged 1 to 79 years (mean age 45 years). In 30 instances cerebral gliomas were involved (low grade 14, high grade 16, according to WHO), 7 cavernomas, 7 metastases, 4 meningiomas and 2 AVM, the gliomas in the spine 1 high grade, the remainder low grade. The patients were examined before and after operation using MR and CT. The symptoms on admission were epileptic seizures (30 patients), hemiparesis (35 patients), speech disorders (11 patients). In spinal processes deficiency motor symptoms with paraesthesias were present. In low grade gliomas total/subtotal resection was achieved in 13/14, in high grade ones in 5/16, while partial resection in low grade gliomas was 1/14, in high grade ones 11/16. A transient postoperative deficit – more marked or new – was present in 8 patients and was found more frequently when the function was impaired already before operation and improved within 2 to 6 weeks. During the postoperative follow up the patients with low grade gliomas (6 to 53 months) 13/14 patients were clinically stable also on MR examination, 1 patient died due to progression of the disease. During the follow up of high grade gliomas (3 to 32 months) 9 patients died, 4 are stable and there was a progression of the disease in 3 patients. Direct peroperative neurostimulation mapping of nerve functions during microneurosurgical elimination of glial tumours from eloquent sites makes their extensive and safe resection possible which may be of benefit in particular in low grade glial tumours. The neurostimulation method makes it also possible to select an optimal approach to lesions which are not gliomas and are located in eloquent cerebral areas. This was used in 20 patients.

        Key words: functional mapping, peroperative monitoring, electrical stimulation, cerebral tumour, pyramidal tract