**10. Use of LITT in epilepsy**

Pharmacoresistant or drug-resistant epilepsy (DRE) is a significant clinical challenge with prevalence of approximately 28 to 40% in patients with epilepsy [139, 140]. In addition, approximately 10% of pediatric patients with epilepsy meet the criterion of DRE within 18 months of diagnosis [140]. Epilepsy surgery has been shown to have beneficial long-term effects in terms of seizure control (seizure free outcome rate of 67 and 26% at 5 and 15 years follow-up, respectively) and psychosocial outcomes in patients with DRE [141–143]. Based on a recent meta-analysis, the incidence of neurological deficits, permanent neurological deficits,

wound infection/meningitis following temporal lobectomy with/without amygdalohippo‐ campectomy and extratemporal lobar/multilobar resections have been reported to be 5.2, 0.8, 1.1 and 19.5, 3.2, 1.9%, respectively [144]. The complication rates have been shown to in‐ crease from 10% during first resective surgery in pediatric patients with complex refractory epilepsy to 50% during second respective surgery [145]. Given this success of epilepsy surgery in controlling seizures with associated morbidity in patients with DRE, there is always a need to improvise on surgical techniques so as to reduce the morbidity while improving the outcomes. Introduction ofMRI-guided LITTin neurosurgery overthe past decades have paved a way to exploration of this technique in patients with DRE. MRgLITT is a minimally invasive stereotactic technique that can be used to ablate the epileptogenic zone and associate fibers so as to simulate the resection and disconnection procedures, respectively. FDA approved Auto LITT in 2009, following a successful Phase 1 multicenter trial investigating the safety of this system in patients with recurrent GBM. In 2012, Curry et al. [146] firstreported the use of MRIguided (1.5T) LITT (Visualase thermal system) in five patents with DRE. In this study, they ablated six epileptic zones (cingulate tuber *n* = 1, mesial temporal sclerosis *n* = 1, hypothala‐ mic hamartoma *n* = 2 and frontal cortical dysplasia *n* = 2) in five patients with DRE and all patients were reported to be seizure-free at 2–13 months of follow up [146]. No complica‐ tions were reported in this study. Another study reported the use of this modality in a 3-yearold with a diagnosis of precocious puberty and pharmacoresistant gelastic seizures and MRI showed type III hypothalamic hamartoma (both pedunculated and sessile component) [88]. Patient underwent MRgLITT using Visualase system without perioperative complications. There was significant improvement in behavior and seizures at 2 weeks after the procedure. At 6 months follow up, patient remained seizure-free with improvement in behavior and selfindulging learning patterns such as playing and entertainment [88]. A year later, Wellmer et al. [147] reported the successful use of 3T MR-guided stereotactic radiofrequency thermal coagulation in two patients with DRE due to type IIB frontal focal cortical dysplasia. These focal cortical dysplasias were identified as epileptogenic zones prior to LITT and one of these lesions was in close proximity to the cortico-spinal tract as elicited by the motor-evoked potentials using in-depth electrodes. Both patients were seizure-free at 12 and 5 months with no persistent postoperative complications (one patient had transient mouth paresis) follow‐ ing thermal coagulation [147]. Authors emphasized the importance of precise placement of radiofrequency probe and destruction of epileptogenic zone, taking into account the sur‐ rounding eloquent area. Gonzalez-Martinez et al. [148] reported robot (ROSA, Medtech Surgical, Inc.) assisted placement of laser probe (Visualase Inc.) under intraoperative MRI guidance to ablate a periventricular heterotopic lesion in a 19-year-old female with DRE of 10 years duration. Authors reported that combination of robot, LITT and intraoperative MRI is a safe, accurate, efficacious and time-efficient minimally invasive technique that can be used for placement and ablation of epileptogenic zone in patients with DRE [148]. Esquenazi and colleagues [149] reported the utility and feasibility of stereotactic MRgLITT (3T) in two patients with DRE and periventricular nodular heterotopia. One patient underwent temporal lobecto‐ my in addition to LITT and was seizure-free during the follow up and another patient had significant seizure control leading to adjustment in medications following the procedure [149]. Former patient with two procedures had transient visual deficit and no complications in another patient were reported during the follow up. Stereotactic placement of multiple trajectories to achieve conformity of complex tumor shapes at deeper locations was also described in this report. Recently, Lewis and colleagues [150] described the feasibility and efficacy of MRgLITT in 17 pediatric patients with DRE using Visualase system. In this retrospective study, 17 patients with DRE underwent 19 MRgLITT procedures with a mean follow up of 16.1 months. Focal cortical dysplasia (*n* = 12) was the most common pathology followed by tuberous sclerosis complex (*n* = 5), hypothalamic hamartoma (*n* = 1), mesial temporal sclerosis (*n* = 1), Rasmussen encephalitis (*n* = 1) and tumor (*n* = 1) [150]. One LITT procedure was aborted and one was partially completed leading to completion of LITT in 17 procedures. Nine patients had prior surgeries including two patients had three, one had two and the rest had one procedure each prior to LITT. Engel class I, class II, class III and class IV outcome were achieved in 41, 6, 18 and 35%, respectively, following LITT with an average postprocedure hospital stay of 1.56 days. 38% of patients with Engel class I/II outcomes and 56% of patients with Engel class III/IV outcomes had at least one resective surgery prior to LITT [150]. Inaccurate fiber placement, device malfunction, inaccurate fiber placement with IVH (aseptic meningitis and ventriculostomy) and post-ablation edema/drug-induced gastritis were noted in one patient each leading to eight individual complications in four patients [150]. Patients with lesions <2 cm in size, well-circumscribed solitary lesions and concordant EEG and presurgical data were considered optimal candidates for LITT ablation in this study [150]. Recently, Patel et al. [98] reported the utility of LITT in 10 patients with pharmacoresistant epilepsy [98]. Total operative time and ablation time were 2.6±0.4 h and 7.6±2.3 mins, respec‐ tively. No procedure-related complications were noted in this study. However outcome in terms of seizures control was not reported in this study [98]. Based on these studies, LITT has shown promising results in patients with DRE, especially those who require repeat resection surgery with favorable outcome while minimizing morbidity. However, long-term prospec‐ tive randomized controlled studies are warranted to validate the efficacy of LITT in patients with DRE and to establish appropriate selection and inclusion criterion to achieve favorable outcomes.
