Abstracts

Rationale: The use of laser interstitial thermal therapy (LITT) for the treatment of mesial temporal lobe epilepsy (MTLE) has become more common. Despite a lower seizure-free outcome compared to classic anterior temporal lobectomy (estimated 65% with an Engel-I outcome vs. 80%), LITT is employed as a less invasive procedure for established diagnosis of MTLE.  It is stipulated that LITT non-responders either have an additional lesion (e.g. temporal neocortical or extra-temporal) or inadequate ablation due to technical limitations  of the method. Here we review data from a case of focal epilepsy with inadequate response to LITT. Methods: A 32 yo right-handed woman with drug-resistant epilepsy (3 focal impaired awareness seizures/month) underwent pre-surgical evaluation. Findings were: Long-term video-EEG - left anterior>mid temporal surface electrodes ictal onsets; MRI - left mesial temporal sclerosis (MTS);  FDG-PET scan - left temporal hypometabolism;  fMRI - left hemisphere language dominance.A LITT procedure was performed to ablate left mesial temporal structures and an intra-operative MRI confirmed the ablated region. She recovered from the surgery without complications and with a decrease in seizure frequency (4 over 6 months). She returned for a left anterior temporal lobectomy 6 months after LITT. Results: Post-LITT MRI  showed an area of necrosis covering the left hippocampus, but leaving some anterior structures, mostly the uncal cortex intact anteriorly . Intra-operative electrocorticography recording showed spontaneous spike/polyspike and wave discharges in the deepest mesial contacts recording from the remaining tissue in the amygdala/uncus and anterior hippocampus. No neocortical discharges were detected . The anterior temporal neocortex and all the mesial structures were removed , with resection posteriorly to complete a standard left anterior temporal lobectomy. The hippocampus appeared necrotic intra-operatively .Pathology revealed a small strip of gliotic cortex with extensive neural loss and near complete necrosis of the underlying white matter with accumulation of histiocytes and marked collagen deposition at the site of the LITT procedure. Conclusions: We review the pre-, intra-, and post-surgical imaging, and the pre- and intra-operative electrographic characteristics of this case, and correlate it with the tissue pathology. The patient has no deficits and has been seizure-free  for 5 months since the resective surgery . Based on the concordant radiologic, pathologic and clinical data, the recurrence of seizures in this patient appears to represent an example of inadequate ablation of medial temporal tissues, as opposed to presence of a secondary focus. This  case provides information for better understanding the effect and limitations of LITT, and for designing future prospective studies for laser ablation for the treatment of MTS. Funding: None.