CORTICAL MAPPING DEMONSTRATES HUMAN SOMATOSENSORY GYRUS IS LARGER THAN MOTOR GYRUS

Craniotomy with intraoperative rolandic cortical mapping was used to e valuate and compare the relative exposed surface areas of somatosensor y gyri (SSG) and motor gyri (MG). The records of patients who underwen t intraoperative photography and electrophysiologic mapping of SSG and MG were reviewed. Patients were excluded if the perirolandic area was involved with tumor or if the operative exposure did not permit adequ ate visualization of perirolandic cortex. Twenty-five patients (10 fem ales, 15 males, median age 31 years) with varying pathologies met thes e criteria. Twenty of the 25 craniotomies were performed on the left s ide. Outlines of the exposed SSG and MG were traced on transparencies, which were then digitized. The areas of the exposed surfaces of SSG a nd MG were computed-in pixels. A ratio (SIM = surface area of exposed SSG/surface area of exposed MG) was computed for each patient. S/M was >1 (surface area of the SSG was larger than the surface area of MG) i n 19 of 25 patients (76%). S/M ranged from 0.79 to 1.62 (median 1.18). These data indicate that the exposed surface area of SSG is usually l arger than MG (p < 0.01). This information may help discern the locati on of the SSG and MG to focus intraoperative cortical mapping and may have utility in the evaluation of functional magnetic resonance imagin g (MRI) and positron emission tomography.