Perioperative use of transcranial magnetic stimulation

A practical means of noninvasively stimulating the cortex was developed in the mid-1980s. Both electrical and magnetic stimulating pulses applied transcranially were shown to be capable of exciting motor cortex. Transcranial magnetic stimulation (TCMS), compared with transcranial electrical stimulation, produced relatively pain-free cortical excitation. This generated interest in developing clinical applications making use of TCMS. This article reviews the basic principles of perioperative TCMS. Two clinical applications that require TCMS are then discussed. The first involves the use of TCMS for monitoring the functional integrity of the spinal cord descending motor paths during surgery. Spinal cord motor path monitoring may have utility because several case reports have suggested that somatosensory evoked potentials may not always predict new postoperative motor deficits. The second application involves the use of discrete TC:MS for localizing eloquent cortex in the preoperative period. The ability to define cortical areas functionally as they relate to surgical pathology is an invaluable aid for planning a surgical approach to their cure. A method under development at the authors' institution for correlating TCMS-derived functional data with anatomical data acquired from magnetic resonance imaging is described, and the use of this method for locating motor and visual association cortices is reviewed.