PREOPERATIVE LOCALIZATION OF THE CENTRAL SULCUS BY DIPOLE SOURCE ANALYSIS OF EARLY SOMATOSENSORY-EVOKED POTENTIALS AND 3-DIMENSIONAL MAGNETIC-RESONANCE-IMAGING

Surgery of lesions within or close to the central area of the brain al ways carries the risk of iatrogenic motor or sensory deficits. Functio nal localization by means of intraoperative direct stimulation of the motor area or by recording somatosensory evoked potentials (SSEP's) fr om the surface of the somatosensory cortex is believed to reduce the o perative risk. The authors introduce the combination of dipole source analysis of scalp-recorded SSEP's with three-dimensional (3-D) magneti c resonance (MR) imaging as a tool for preoperative localization of th e central sulcus. This provides information on both functional and str uctural localization for preoperative planning. Four repeated measurem ents of right and left median nerve SSEP's were obtained from 20 subje cts. Dipole source analysis showed a retest reliability of the 3-D loc alization error of 2.9 +/- 2.0 mm. Compared to the MR evaluation, dipo le source analysis was found to mark the central sulcus within 3 mm fo r 15 conditions (subjects X side of stimulation), while the 3-D MR mea surement was accurate to within 6 mm for 10 conditions and 9 mm for 14 conditions. Dipole locations were confirmed in six patients who under went surgery of the central region. With respect to this application, dipole source analysis combined with 3-D MR imaging appears to be a va luable tool for preoperative functional localization. The accuracy in localization will be further improved when realistic head models becom e available that can take into account individual head geometry. Furth er development of the proposed new method holds promise that evoked po tentials and electroencephalography will gain greater use in presurgic al functional localization.