Abstracts

Rationale: We reported recently on the factors predicting a seizure free status following a standard anterior medial temporal resection (SAMTR). This study revealed that during an intracranial electrode study, rapid seizure spread to the temporal neocortex from a mesial onset was associated with a statistically significant failure to control seizures with an SAMTR. This paper aims to identify the non-invasive markers as predictors for seizure freedom following extended temporal lobectomy (ETL). Methods: A cohort of 25 patients undergoing SAMTR (4cm or less lateral neocortical resection along with mesial structures) or ETL (greater than 4cm lateral neocortical resection) for medically refractory seizures were evaluated for seizure free status post operatively. The SAMTR patients were matched for age and duration of epilepsy to be used as controls for the ETL group. This former group was further divided into those with good and poor outcomes based on the absence or presence of seizures respectively. All cases with ETL had good outcomes. Post-operative seizure status was classified based on the Engel classification system; Class I (good outcome), Class II, III, and IV (poor outcome). Fifty-six scalp and intracranial electroencephalograms (icEEG) were assessed for initial extent of onset and subsequent rate of spread to the temporal neocortex or extratemporal regions and rated as fast/slow spread. A preoperative positron emission tomogram (PET) was analyzed for the distribution of hypometabolism in the ipsilateral temporal lobe for each patient. All cases included had non-lesional etiologies in addition to mesial temporal sclerosis (MTS). Patients with neoplasms, cavernomas, lateral neocortical resections only or if combined with extratemporal procedures were excluded from the study. Results: IcEEG analysis revealed a focal onset with a rapid spread (<10 seconds from time of onset) outside the mesial temporal lobe for cases with ETL (75% of cases) and for those with SAMTR (100%) with poor outcomes. Similarly, the scalp EEG recordings had a diffuse temporal onset with a rapid spread to the entire ipsilateral hemisphere in under 12 seconds for the ETL group (75% of seizures) and the SAMTR with poor outcome (100% of seizures). The median time for spread outside the temporal lobe to the ipsilateral hemisphere for all seizures was found to be 12 seconds.  On the other hand, all SAMTR with good outcomes had a focal temporal onset with very slow spread to the ipsilateral hemisphere on scalp EEG. The PET localized medial temporal in 33% of cases that had good outcomes following SAMTR, but involved the entire temporal lobe in 67% in the SAMTR cases that failed. The ETL cases however, localized to the entire lobe or the lateral temporal neocortex in 100% of cases. Conclusions: Our study confirmed that rapid spread from a mesial temporal onset was associated with a poor outcome following a SAMTR. Diffuse temporal onset with rapid spread to the ipsilateral hemisphere, and hypometabolism localized to the entire or lateral aspect of the temporal lobe are useful non-invasive tools to predict the potential for poor outcome. These can be used to guide the need for further evaluations and the extent of treatment to control the seizure network. Funding: None applicable