Abstracts

Rationale: In selected patients with medically intractable mesial temporal lobe epilepsy (MTLE) surgical resection can provide significant benefit in reduction or elimination of their seizures. The standard approach involves craniotomy for resection of the hippocampus as well as variable amounts of amydgala and temporal neocortex. Associated procedural risks limit this therapy in patients who are poor surgical candidates. A novel therapy, laser interstitial thermal (LIT) therapy offers a minimally invasive approach to lesioning mesial temporal lobes structures in these patients. We report early radiographic changes in our series of patients who underwent LIT therapy for MTLE. Methods: Ten consecutive patients underwent LIT procedures for MTLE diagnosed via imaging and electrographic monitoring. LITT was performed using the Visualase system (Visualase, Inc., Houston, TX). This uses a 980-nm laser diode to provide real-time thermal ablation under phase-contrast MRI guidance. MR imaging sequences were obtained on a 3T MR scanner during lesioning and additionally at standard 6 week (early) and 6 month (late) post-therapy time points. Statistical analysis was performed using Fisher's exact test and a p-value of 0.05 deemed significant. Results: All patients underwent uncomplicated ablation of the hippocampus, 6 (60%) on the right side and 4 (40%) on the left. Mean clinical follow-up was 105 days (range 38-239). At time of last follow-up, 8 (80%) of patients were Engel class 1, one (10%) was class 3 and one (10%) was class 4. All patients demonstrated stereotyped changes on MRI at immediate, early and late time points. Qualitative characteristics of the ablation zone and interface on T1, T1 with contrast, T2, FLAIR, ADC and GRE sequences are reported in Table 1. Average area of ablation as measured on contrast-enhanced T1 sequences was 2053 mm³ (range 619-3624). Cerebral edema adjacent to the ablated tissue was noted in 4 (40%); this did not qualitatively impact immediate recovery or relate to post-therapy Engel classification (p = 0.44). Conclusions: In our series, patients undergoing LITT for mesial temporal lobe epilepsy had no significant procedural complications and display at least equivalent clinical outcomes on early follow-up when compared that described in the literature for open surgical resection. The ablated area demonstrates characteristic features on MRI that can be used to confirm delivery of thermal energy as well as serve as a marker of treatment area. Post-therapy cerebral edema and area of ablation did not significantly impact rates of seizure reduction and/or freedom. Long-term imaging follow-up will be important in further characterization of MRI changes over time in patients undergoing LIT therapy.