Presurgical functional mapping of the sensorimotor area using evoked magnetic fields

: In the present study, we evaluated the usefulness of magnetoencephalography (MEG) for presurgical identification of not only the central sulcus by somatosensory evoked magnetic fields (SEFs), which is a well-known, reliable technique, but also the primary hand motor area by movement-related cerebral magnetic fields (MRCFs). Subjects were 10 patients with brain tumor (6 glial tumors, 3 cavernous angiomas, and 1 metastatic tumor) around the sensorimotor area. Identification of the central sulcus by SEF responses to multiple sites of stimulation (median nerve, tibial nerve, thumb, and lower lip) was performed in all patients, and identification of the hand motor area by MRCF responses to the index finger extension task was made in 9. All MEG data were superimposed on sectional or three-dimensional magnetic resonance (MR) images. The central sulcus was clerAly identified by SEFs in all patients, even in 5 whose MR images showed severe distortion, and the primary hand motor area was identified by MRCFs in 6 of 9 patients. The central sulcus and primary motor area identified by MEG were confirmed by cortical recording of somatosensory evoked potentials in response to median nerve stimulation in 7 patients and motor evoked potentials in response to direct cortical stimulation in 5. All patients underwent tumor removal guided by functional mapping by MEG and experienced no surgical complications. In conclusion, MEG is a useful tool in presurgical functional mapping of the sensorimotor area. This is the first report of a case in which identification of the hand motor area by MRCFs was used in a clinical setting.