Introduction: Laser interstitial thermal therapy (LITT) has demonstrated 50-60% seizure freedom at 1-year follow-up in patients with mesial temporal lobe epilepsy (mTLE), with upwards of 60-71% seizure freedom in those with mesial temporal sclerosis (MTS). Reports to date have been confined to relatively small single-institution series.[1–6] We therefore aimed to investigate patient-related and surgical factors associated with seizure outcome from LITT for mTLE in a large cohort across multiple epilepsy centers.

Methods: This multicenter, retrospective cohort study included 87 patients across 8 centers who underwent amygdalohippocampal complex (AHC) LITT for mTLE. Aggregation, deidentification, normalization, and comparison of patient images and clinical data was accomplished with CranialCloud and CranialSuite. Ablation cavities were manually traced on the immediate postoperative MRI. To compare the specific ablation location across patients, all scans underwent non-linear registration to common atlas space derived from 7T MRI.[7–12] A probability map was calculated in atlas space by aggregating normalized ablation cavities and their associated clinical outcome.

Results: At last follow-up 62.1% achieved seizure freedom (73.2% in MTS; 52.2% in non-MTS). Volume of amygdala or hippocampus ablated was not related to seizure outcome. Normalization of ablation cavities demonstrated significant variability in ablation location. Seizure freedom was associated with more anterior and medial ablations; while ablations posterior to the lateral mesencephalic sulcus were associated with no more than 50% chance of seizure freedom [Fig1].

Conclusions: This study is the largest series of AHC LITT for mTLE. Our findings echo prior reports and further support the importance of selecting patients with MTS. The wide variation in ablation location along with its association with seizure outcome highlight the importance of understanding proper targeting. Targeting the uncus, amygdala, and hippocampal head are associated with seizure freedom; while extending the ablation more posteriorly has diminishing returns and has been associated with visual complications.

Patient Care: This research will improve patient care by furthering our understanding about appropriate patient selection and surgical technique for stereotactic laser interstitial thermal therapy for the treatment of drug-resistent mesial temporal lobe epilepsy.

Learning Objectives: 1) To assess the importance of mesial temporal sclerosis in laser interstitial thermal therapy for mesial temporal lobe epilepsy. 2) To understand the variability in surgical technique that exists with laser interstitial thermal therapy for mesial temporal lobe epilepsy. 3) To analyze the effect of laser ablation volume and location on outcomes in mesial temporal lobe epilepsy.

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