Open Access: Optimization of Curvilinear Needle Trajectories for Transforamenal Hippocampotomy

Epilepsy has a point prevalence of about 0.6% globally and accounts for 1% of the global burden of disease in terms of disability-adjusted life-years.1,2Forty-seven percent of patients are seizure-free with their first antiepileptic drug, and an additional 13% are seizure-free with their second antiepileptic drug.3 Thus, about 40% of patients are refractory to medical therapy, and many of them are potential surgical candidates. Although epilepsy surgery outcomes reflect seizure-free rates of 70% to 80%,4-6 only a small fraction of potential surgical candidates are referred for treatment, in part because of physician bias against the highly invasive surgery.7,8 Furthermore, the invasiveness of current surgical procedures likely causes many otherwise eligible patients to forgo surgery despite the high likelihood of a seizure-free outcome.

In recent years, needle-based thermal ablation has been investigated as a minimally invasive alternative to selective amygdalohippocampectomy (SAH). An SAH resection is less aggressive than standard anterior temporal lobectomy but has demonstrated equivalent or nearly equivalent outcomes.5Parrent and Blume9 reported amygdalohippocampotomy by magnetic resonance (MR) imaging (MRI)–guided radiofrequency ablation; seizure outcomes were worse than with anterior temporal lobectomy. However, more recent clinical trials using MRI-guided laser ablation systems have more positively indicated the efficacy of percutaneous thermal ablation for epilepsy. Curry et al10 reported seizure freedom at the 3-month follow-up for 5 pediatric patients treated using the Visualase Thermal Therapy System (Medtronic, Dublin, Ireland). For a small series of procedures using the Visualase laser, Willie et al11 reported 6-month seizure freedom for 7 of 13 patients and substantial improvement for an additional 3 patients. Hawasli et al12 effectively treated 1 case of medically refractory epilepsy using the Monteris Neuroblate System (Monteris, Plymouth, Minnesota). Despite some promising results, these ablation procedures to date have not matched the success of SAH. One of the primary limitations of current laser-induced thermal therapy procedures is that the laser probes used with currently available devices are restricted to linear trajectories, which cannot lesion the entire hippocampus, even with directionally aiming probes. Additionally, these procedures still require full operating room preparation for twist-drilling the skull.

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