Intraoperative localization of the central sulcus by cortical somatosensory evoked potentials in brain tumor. Case report.

Perplexing findings of cortical somatosensory evoked potentials (SEP's) for determining the central sulcus during a craniotomy are reported in a case of brain tumor. On stimulation of the contralateral median nerve in that patient, phase-reversal of SEP waves N1 and P2 was observed not only across the central sulcus but also across the precentral sulcus. In topographic mapping of the N1-P2 amplitude, the sulcus dividing the maximum polarity was the central sulcus; this was confirmed by the cortical stimulation-evoked motor responses. For accurate localization of the central sulcus by cortical SEP's, the distribution of potentials must be analyzed with extensive exposure of the sensorimotor cortex.