Image guidance has been used in several aspects of epilepsy surgery, including the removal of deep lesions, selective amygdalo-hippocampec-tomy, callosotomy, temporal resection, cortical resection and the placement of depth electrodes . The hippocampus and the corpus callosum are relatively fixed structures, and there is only minimal brain shift along the anteroposterior axis. Once hippocampal resection has begun, however, CSF drainage and the mesial displacement of the brain due to gravity lead to error in the mesio-lateral plane. According to Olivier et al. , this did not lead to interference with localization and gross total resection of the mesial structures.
In transylvian selective amygdalo-hippocampectomy, surgical orientation is achieved primarily through the exposure of anatomical landmarks, namely the uncus and the sulcus circularis insulae. This requires a wide opening of the Sylvian fissure with the associated risks of vessel injury and vasospasm. Image guidance allows orientation without the necessity to expose and identify such landmarks. Trajectories to the hippocampus and resection borders can be defined pre-operatively. Image guidance directs trans-sulcal dissection and also ensures complete resection of the relevant hippocampal structures; the outcome of epilepsy surgery has been shown to be closely related to complete hippocampal resection.
The location of focal cortical dysplasia is often difficult to identify macroscopically. Image guidance allows accurate anatomical correlation in cortical resections, and this becomes more accurate if the system is used concurrently with electrocorticography and motor mapping. It also facilitates the confirmation of the length of a callosal section, and in temporal lobectomy it aids a decision on the volumes of lateral temporal cortex and hippocampus that can safely be resected.
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