Abstracts

Rationale: Epilepsy surgery is difficult when uncertainty of the epileptogenic zone persists despite multimodal presurgical evaluation. In such cases, a minimally invasive therapeutic challenge of thermal ablation is an attractive management option when compared to craniotomy. Though the laser thermocoagulation technique is ideally suited for this approach, it has yet to become available and cost-effective in many countries. We sought to evaluate a novel stereotactic volumetric radiofrequency ablation (vRFA) technique to deliver a therapeutic challenge and better delineate the extent of the epileptogenic zone in ‘difficult-to-treat’ refractory focal epilepsies, both lesional and nonlesional. This technique also differs fundamentally from beside RF thermocoagulation traditionally done using Stereo-EEG electrodes in that it is done 1) in the operating room under anesthesia and 2) using multiple stereotactic trajectories and conventional RF ablation probes.

Methods: Patients undergoing the stereotactic vRFA procedure between January 2016 and Jan 2021 were included in the study for retrospective analysis. The vRFA technique involves stacked RF lesions generated using a conventional RF generator at multiple target points within multiple stereotactic trajectories eventually summating to provide an ‘ablative cone’ in the cortical regions felt to be epileptogenic after non-invasive and/or invasive evaluations. Patients with a minimum of 2 months of post-operative follow-up were included in this study.

Results: Twenty-two patients underwent vRFA procedures and had a mean follow-up period of 15.9 ­+ 9.2 months. MRI was negative or subtle in 9 (41%). Stereo-EEG was performed in 19 patients. Ablative targets were insulo-opercular (6), peritrigonal/paraventricular (4); paracentral lobule (3); orbito-frontal (2), cingulate (2), lingual (2), temporo-parietal (2), and cuneus/occipital (2). Fourteen patients (63%) remained seizure-free on last follow-up. Overall, 17 had a favorable response to vRFA challenge characterized as > 2 months of seizure-freedom. Amongst the seizure-free patients, two were seizure free after the initial favorable response to vRFA was followed by craniotomy and cortical topectomy of the lesioned area following seizure relapse. Two patients were rendered seizure free after cortical resection despite no initial favorable response to vRFA. Five patients who were not seizure-free on last follow-up did have an initial favorable response, of whom two are awaiting resection. Noteworthy sensorimotor deficits in 3 (permanent in one), visual field deficits in two, and cognitive deficits in one patient occurred.

Conclusions: Stereotactic vRFA is a minimally invasive thermoablative technique using low-cost conventional RF lesioning hardware that may be useful 1) as a minimally invasive test of hypothesis in difficult-to-treat epilepsy surgeries and 2) in countries lacking the latest laser thermoablative technology. The safety and long term efficacy warrant verification prospectively.

Funding: Please list any funding that was received in support of this abstract.: None.