Relationships between the epileptic focus and hand area in central epilepsy: combining dipole models and anatomical landmarks

Object. When considering resection of epileptic generators near the central sulcus, it is essential to define the spatial relationship between the epi leptic generator and the primary sensorimotor hand area. In this study, the authors assessed the accuracy of dipole modeling of electroencephalographi c spikes and median nerve somatosensory evoked potentials (SSEPs) in defini ng this relationship preoperatively and noninvasively. Methods. Epileptic spikes and SSEPs in patients with focal central area epi lepsy were represented by dipole models coregistered onto global magnetic r esonance images. In patients who underwent surgery, spike dipoles were also compared with findings of electrocorticography (ECoG) and with the resecti on area. To improve the accuracy of the dipole models, anatomical landmarks of the hand area were used to assess the error in SSEP dipole location, an d this error measure was used to correct the location of spike dipoles. Five patients with central epilepsy were studied, three of whom underwent E CoG-guided surgical resections. The location of SSEP dipoles correlated wel l with anatomical landmarks of the primary sensory hand area. The relative position of the spike and SSEP dipoles correlated well with the patients' i ctal symptoms, ECoG findings, and the location of the epileptic focus las d efined by the resection cavity in patients who became seizure free postoper atively). Corrected spike dipoles were located even closer to the resection cavity. Conclusions. The calculation of the relative location of spike and SSEP dip oles is a simple noninvasive method of determining the relationship between the primary hand area and an epileptic focus in the central area. The spat ial resolution of this technique can be further improved using easily ident ifiable anatomical landmarks.