Abstracts

Rationale: Magnetic resonance thermometry-guided stereotactic laser amygdalohippocampotomy (SLAH) is increasingly being used as a surgical approach to treat patients with epilepsy in the setting of mesial temporal sclerosis. Although successful for the majority of patients, ~1/3 of patients experience seizure recurrence following this procedure. In cases where not all targeted amygdalohippocampal tissue was actually eliminated, repeat SLAH can improve outcomes. However, for many patients, seizure recurrence likely indicates an ictal onset zone outside of the ablated mesial structures. In this study, we explore the role of intracranial monitoring including stereoelectroencephalography (SEEG) in determining seizure onset following SLAH failure. Methods: We present data for 6 patients (5 male, 1 female ages 25-62) who were treated at our center between 2011 and 2017. These patients underwent SLAH without initial intracranial monitoring but continued to experience postoperative seizures and were subsequently re-evaluated by intracranial monitoring. All patients had undergone initial presurgical evaluation consisting of video EEG monitoring, PET and MRI scans, and neuropsychological testing and were determined to be candidates for SLAH by a multidisciplinary team. Demographic information, semiology, imaging data, intracranial monitoring results, subsequent surgical interventions, and outcomes were analyzed. Results: Of the 6 patients identified, 5 were evaluated with sEEG and 1 patient was evaluated using a combination of subdural grid/strip and depth electrodes. Remaining seizure foci were determined to be contralateral mesial temporal (2 patients, one of whom also had seizures arising from the ipsilateral mesial temporal remnant structures), residual mesial amygdala, entorhinal cortex, and parahippocampal gyrus (1 patient), parahippocampal gyrus (1 patient), posterior cingulate (1 patient), and poorly localizing to anterior temporal region (1 patient). 4 of these patients underwent repeat laser ablation targeted to area of seizure onset identified by intracranial monitoring and 2 underwent anterior temporal lobectomy. Patients experienced either seizure freedom (3 patients) or improvement seizure frequency (3 patients, Engel class IIB, IIB, IIIA) following repeat procedure.  Conclusions: Intracranial monitoring including minimally invasive SEEG can be effective in identifying the ictal onset zone in cases of seizure recurrence following SLAH.  Furthermore, initial laser ablation does not preclude patients from further intracranial monitoring followed by additional laser ablation or open resection. Funding: None