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Epilepsy
Research paper
Stereotactic EEG-guided laser interstitial thermal therapy for mesial temporal lobe epilepsy
  1. James X Tao1,
  2. Shasha Wu1,
  3. Maureen Lacy2,
  4. Sandra Rose1,
  5. Naoum P Issa1,
  6. Carina W Yang3,
  7. Katherine E Dorociak2,
  8. Maria Bruzzone1,
  9. Jisoon Kim1,
  10. Ahmad Daif1,
  11. Jason Choi4,
  12. Vernon L Towle1,
  13. Peter C Warnke4
  1. 1 Department of Neurology, The University of Chicago, Chicago, Illinois, USA
  2. 2 Department of Psychiatry, The University of Chicago, Chicago, Illinois, USA
  3. 3 Department of Radiology, The University of Chicago, Chicago, Illinois, USA
  4. 4 Department of Neurosurgery, The University of Chicago, Chicago, Illinois, USA
  1. Correspondence to Dr James X Tao, Department of Neurology, The University of Chicago, Chicago, IL 60637, USA; jtao{at}neurology.bsd.uchicago.edu

Abstract

Objective To determine the outcomes of combined stereo-electroencephalography-guided and MRI-guided stereotactic laser interstitial thermal therapy (LITT) in the treatment of patients with drug-resistant mesial temporal lobe epilepsy (mTLE).

Methods We prospectively assessed the surgical and neuropsychological outcomes in 21 patients with medically refractory mTLE who underwent LITT at the University of Chicago Medical Center. We further compared the surgical outcomes in patients with and without mesial temporal sclerosis (MTS).

Results Of the 21 patients, 19 (90%) underwent Invasive EEG study and 11 (52%) achieved freedom from disabling seizures with a mean duration of postoperative follow-up of 24±11 months after LITT. Eight (73%) of 11 patients with MTS achieved freedom from disabling seizures, whereas 3 (30 %) of 10 patients without MTS achieved freedom from disabling seizures. Patients with MTS were significantly more likely to become seizure-free, as compared with those without MTS (P=0.002). There was no significant difference in total ablation volume and the percentage of the ablated amygdalohippocampal complex between seizure-free and non-seizure-free patients. Presurgical and postsurgical neuropsychological assessments were obtained in 10 of 21 patients. While there was no group decline in any neuropsychological assessment, a significant postoperative decline in verbal memory and confrontational naming was observed in individual patients.

Conclusions MRI-guided LITT is a safe and effective alternative to selective amygdalohippocampectomy and anterior temporal lobectomy for mTLE with MTS. Nevertheless, its efficacy in those without MTS seems modest. Large multicentre and prospective studies are warranted to further determine the efficacy and safety of LITT.

  • temporal lobe epilepsy
  • anterior temporal lobectomy
  • drug resistant epilepsy
  • laser ablation
  • selective amygadalohippocampectomy

https://doi.org/10.1136/jnnp-2017-316833

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    Introduction

    Epilepsy surgery has been the ‘gold standard’ treatment for patients with medically refractory epilepsy. Temporal lobe epilepsy (TLE) is the most common focal epilepsy in adults.1 Seizure freedom can be achieved in 60%–80% of patients with TLE after selective amygdalohippocampectomy (SAH) or anterior temporal lobectomy (ATL).2–4 Nevertheless, traditional epilepsy surgeries that require craniotomy carry a significant risk of surgical complications and neurocognitive impairments,5 6 which often deter patients from considering the surgery. Consequently, epilepsy surgery has been significantly underused across epilepsy centres.7

    Minimally invasive surgical procedures, such as stereotactic radiosurgery, radiofrequency thermal ablation and MRI-guided stereotactic laser interstitial thermal therapy (LITT), have been developed to mitigate the risk of surgical complications and neurocognitive impairments associated with traditional epilepsy surgery.8 9 MRI-guided stereotactic LITT appears to be an attractive technique with several advantages over other techniques, including real-time monitoring of ablation volume with MRI thermometry, preventing off-target injury with temperature threshold, sharp lesion demarcation and immediate efficacy.10 11 Early data suggest that LITT might be a safe and effective treatment for patients with medically refractory mesial temporal lobe epilepsy (mTLE).12–15 None of these studies though have systematically used invasive EEG recordings to outline the epileptogenic zone and guide the ablation. Ablation based on anatomy alone can fail if the ictal onset zone (IOZ) was not covered, reducing the therapeutic efficacy of LITT. We report here the outcomes in 21 patients with mTLE who underwent invasive EEG consisting of stereo-electroencephalography (SEEG) with depth electrodes+/-subdural strip electrodes and LITT at the University of Chicago epilepsy centre and further assess the safety and efficacy of LITT for patients with medically refractory mTLE.

    Methods

    Patient selection and intracranial EEG recording

    We enrolled 21 patients with drug-resistant mTLE who underwent MRI-guided stereotactic LITT at the University of Chicago Medical Center from January 2014 to October 2017. One patient diagnosed with both mTLE and psychogenic non-epilepsy seizures (PNES) was excluded from the outcomes analysis due to the uncertainty of postoperative seizures versus PNES. All patients received a standard presurgical evaluation, which included a comprehensive neurological history and examination, inpatient video-EEG monitoring, brain MRI with volumetric 1.0 mm-section T1 coronal and fluid-attenuated inversion recovery (FLAIR) images to assess hippocampal volume, 18-fluorodeoxyglucose positron emission tomography (FDG-PET), neuropsychological evaluation and functional MRI (fMRI). Magnetoencephalography and Wada tests were also obtained when clinically warranted.

    Invasive EEG recording with depth (SEEG)+/-subdural strip electrodes was performed in all but two patients. Invasive EEG monitoring was performed when the seizure onset zone was inadequately lateralised or localised to the mesial temporal lobe during non-invasive evaluations. Findings that suggested possible temporal neocortical, extratemporal and bilateral temporal epileptogenesis included a normal brain MRI, 2–4 Hz scalp temporal ictal onset, atypical seizure semiology (ie, hyperkinetic) for TLE, frequent scalp temporal interictal spikes (>60 spikes per hour) and bilateral mesial temporal sclerosis (MTS).16 17 In a standard implantation, unilateral or bilateral depth electrodes (12 contacts with 5 mm spacing) were placed along the longitudinal axis of hippocampus through an occipital approach to sample the amygdalohippocampal complex (AHC). Three lateral temporal depth electrodes (12 contacts and 5 mm spacing) or subdural strip electrodes (6 contacts with 10 mm spacing) were placed through a lateral temporal burr hole to sample anterior, mid and posterior temporal cortex. One to two depth electrodes were sometime implanted to sample the orbitofrontal cortex through a frontal burr hole. The location of implanted intracranial electrodes was validated by intraoperative stereotactic CT and coregistered to the patient’s non-deformed presurgical 3D brain MRI images using a geometry-based technique (figure 1C). Average fiducial point discrepancy was less than 1.0 mm.18

    Figure 1
    Figure 1

    Ablation of mesial temporal lobe using stereotactic MRI-guided LITT: temperature measurement with MRI thermometry during the ablation with optimal temperature between 60°C and 80°C (A). Depiction of irreversible lesion zone at the completion of ablation in the axial (B) and postablation axial T1 image with gadolinium contrast enhancement of lesion zone (D). A basolateral view of coregistration of intracranial depth and subdural electrodes with preimplantation brain MRI and postimplantation CT images (C). LAT1, the first contact on the left anterior temporal 1×6 subdural electrode strip; LHD1, the first contact of the left 1×12 hippocampal depth electrode; LITT, laser interstitial thermal therapy; LMT1, the first contact on the left middle temporal 1×6 subdural electrode strip; LPT1, the first contact on the left posterior temporal 1×6 subdural electrode strip.

    Simultaneous scalp and invasive EEG were recorded using Xltek, Natus Medical Incorporated (Pleasanton, California, USA) at a sampling rate of 1000 Hz. Scalp EEG was recorded according to the international 10–20 system with additional six subtemporal electrodes (F9, T9, M1, F10, T10 and M2). Scalp and intracranial EEG were analysed with high-pass filter of 1 Hz and low-pass filter of 70 Hz, 15 s/page and sensitivity of 10 µV/mm (scalp) and 100 µV/mm (intracranial). High-frequency oscillations (HFOs) were analysed with high-pass filter of 80 Hz, low-pass filter open, 5 s/page and 7–15 µV/mm sensitivity. HFOs were defined as events containing at least four consecutive oscillations of frequencies above 80 Hz and amplitudes distinctly higher than surrounding background.19 The IOZ was defined as the contacts where the seizure first started.

    Patients were eligible for LITT when their seizure onset was localised to mesial temporal cortex during the invasive EEG study or in two cases when their brain MRI showed a unilateral MTS that was concordant with other non-invasive data including clinical, electrophysiological, FDG-PET and fMRI. The risks and benefits of both LITT and standard ATL or SAH were discussed with patients who then made the decision as to the surgery with which to proceed. MTS was defined as the presence of MRI T2/FLAIR hyperintensity with reduced hippocampal volume and/or loss of hippocampal internal architecture.20

    MRI-guided stereotactic LITT

    The surgical technique used for MRI-guided stereotactic LITT was similar to that described previously.13 14 21 Briefly, patients were placed in a MRI compatible stereotactic head frame (CRW Integra Neurosciences, Plainsboro, New Jersey, USA). A 1.0 mm-section stereotactic CT was obtained intraoperatively and subsequently fused with a 1.0 mm-section volumetric gadolinium-enhanced T1-weighted MRI using Stealth software (Medtronic, Minnesota, USA) with the depth electrodes in situ. Under generalised anaesthesia, an applicator assembly consisting of a 1.65 mm diameter outer polycarbonate cooling catheter containing an inner 400 µm diameter optical fibre (Visualase Medtronic, Minnesota, USA) was implanted along the longitudinal axis of the AHC through an occipital 3.2 mm trephination using frame-based stereotaxy. At the end of the implantation, another intraoperative CT was obtained to confirm the laser fibre position and coregistration to the MRI was again performed to assure exact fibre position in the planned trajectory and coverage of the electrode contacts from which seizure onset was recorded. The patient was then transferred from the operating room to a dedicated 3 Tesla MRI scanner (Philips, Amsterdam, The Netherlands) for MRI-guided thermal ablation. To avoid off-target thermal injury, specific temperature safety limits were set in the inferior, ventro-oral thalamus, basal ganglia and mesencephalon to automatically terminate laser delivery if the temperature in these structures exceeded 43°C.

    The location and volume of the intended ablation was determined based on the results of intracranial EEG monitoring, including IOZ and the areas of HFOs and immediate ictal spreading in patients who underwent invasive EEG recording. AHC was directly targeted for ablation in two patients without invasive EEG recording. A test ablation at 5 W was performed to visualise the expected heat distribution from the fibre and test the phase-shift imaging for temperature monitoring. The initial ablation was made at the anterior margin of the AHC and then the laser fibre was retracted along the anterior-posterior axis at 0.5–1.0 cm intervals to complete 3–5 ablations at temperatures between 60°C and 80°C (figure 1A). Real-time MRI images of the temperature around the probe, calculated with the Arrhenius equation, were monitored to estimate the volume of permanent damage based on the 70°C contour (figure 1B). This resulted in an ellipsoid lesion as assessed by intraoperative MRI with gadolinium contrast and volumetry (Precise software Inomed, Germany). All lesions were made in a standardised fashion at the 60% maximum lesion energy level (ie, 9 W). At the completion of the ablation procedure, a 1.0 mm-section gadolinium enhanced T1-weighted sequence with contrast was acquired to assess the final ablation volume (figure 1D). The laser probe and cranial fixation device were then removed. The incision was irrigated and closed with a single suture. Patients were subsequently transferred to the neuro-intensive care unit for postoperative care and treated prophylactically with a 3-day taper of Dexamethasone to reduce postablative oedema. All patients were treated by the same neurosurgeon (PCW).

    Assessment of ablation volume

    Volumetric assessment of the ablation volume was performed by two investigators independently by using stereotactic software (Precis, Inomed, Freiburg, Germany) on all cases. AHC volumes were assessed from FLAIR images in coronal and axial dimensions. The immediate postablation T1-weighted postcontrast images were used to assess the lesion volume. The rim of contrast enhancement was drawn on these contiguous 1 mm slices and 3D volumes calculated from interpolated thin slices. Inter-rater agreement was tested using Kappa statistics.

    Assessment of seizure outcomes

    Seizure outcomes were assessed during clinical follow-up visits at 3, 6, 12 months and yearly thereafter surgery; in addition, the status of seizure freedom at the time of most recent follow-up was reported. Preoperative antiepileptic drugs (AEDs) were maintained at least for 6 months after LITT and in some cases were reduced thereafter if patients remained seizure-free. Given that the postsurgical follow-up duration was less than 1 year in 3 of the 21 patients in this study, seizure outcomes were categorised into four classes similar to Engel’s classifications including: class I, seizure-free without auras (IA), with auras only (IB), disabling seizures after surgery, but remained seizure-free for more than 2 years (IC) and seizures on medication withdrawal only (ID); class II, fewer than 3 seizure days per year; class III, greater than 80% reduction in seizure frequency and class VI, less than 80% reduction in seizure frequency.14 22 23 The primary outcome was the time to first seizure recurrence. Acute postoperative seizures that occurred within 7 days after surgery were not counted as recurrent seizures.24 Seizures occurring after missing multiple AED doses or after supervised reduction of more than one AED were not considered recurrent seizures if seizure freedom was regained after resuming the mediations.23

    Neuropsychological assessment

    Standardised neuropsychological measures were administered as a part of presurgical and postsurgical assessments. The Wechsler Memory Scale-Fourth Version Logical Memory subtest (WMS-IV LMI, LMII) and the California Verbal Learning Test-Version II Delayed Free Recall (CVLT-II) were used to assess verbal learning and memory. Confrontation naming was assessed using the Boston Naming Test (BNT).12 14 25

    Statistical analysis

    Kaplan-Meier curves were generated using the time to first seizure. Cox regression analysis was performed to determine the HR of MTS. Wilcoxon rank sum test was used to compare the total ablation volume and the percentage of AHC ablated between patients with class I outcome and those with class II, III and IV outcomes. Statistical significance was defined as P<0.05. Neurocognitive deficits prior to and after surgery were examined by identifying the patients who displayed worsened cognitive impairment, defined as 1 SD below normative references. Reliable change indices (RCI) were employed to determine if there had been significant changes between each subject’s baseline and postoperative neuropsychological performance.26 27 A 90% CI was used in this study since it has been commonly used in epilepsy research.28

    Results

    Patient characteristics and intracranial EEG recording

    Twenty-one patients were enrolled in this study, including the first patient who underwent LITT in our epilepsy centre. The mean age was 40±13 years (range: 20–65 years). The mean duration of epilepsy was 22±14 years (range: 3–57 years). Of the 21 patients, 12 (57%) were female; 11 (52%) patients had MTS; 19 (90%) had temporal PET hypometabolism. Invasive EEG monitoring with hippocampal depth electrodes implanted from an occipital approach with lateral temporal depth or subdural electrodes was performed in 19 of 21 patients. IOZ was localised to AHC on the mesial temporal depth electrode ranging from 1 to 8 contacts in all 19 patients. HFOs were also visualised in all 19 patients and ictal HFOs appeared in a smaller spatial extent than their conventional IOZs in all the patients. Sixteen of the 19 patients had seizure onset originating exclusively from ipsilateral AHC. Two patients (patients 18 and 19) had seizure onset originating from AHC extending to ipsilateral mesial anterior temporal tip and underwent ablation of AHC and mesial anterior temporal tip. One patient (patient 20) had bilateral mesial temporal seizure onsets (left-to-right ratio of 10:1) and underwent ablation of left AHC. Demographics and surgical outcomes are summarised in table 1.

    View this table:
    Table 1

    Demographics and surgical outcomes

    Seizure outcome

    After LITT, 11 (52%) of 21 patients achieved freedom from disabling seizures (class I outcome) with a mean duration of postoperative follow-up for 24±11 months (range from 7 to 43 months). Eight (73%) of 11 patients with MTS achieved freedom from disabling seizures (Class I), whereas only 3 (30%) of 10 patients without MTS achieved freedom from disabling seizures. Patients with MTS were significantly more likely to become completely seizure-free (Class IA) after LITT, as compared with those without MTS (HR of MTS=0.12, 95% CI 0.03 to 0.48, P=0.002). Among the 11 patients who achieved class I outcome, 6 patients became seizure-free without aura (IA); 2 became seizure-free with auras (IB) and 1 patient had seizures within the first postoperative month and has remained seizure-free for more than 2 years (IC) and 2 patients had seizures only on medication withdrawal (1D).

    Of the patients who experienced recurrent seizures, all had their first seizures within the first year of the surgery and nine patients had their first seizures within the 6 months, except for two seizures provoked by medication withdrawal (table 1). No patients had increased seizure frequency or severity after LITT. Kaplan-Meier curves illustrated the time to first seizure after LITT in the enrolled 21 patients and in those with and without MTS (figure 2A). The total ablation volume was 2.9±1.2 cm3 in patients with class I outcome and 2.0±1.8 cm3 in patients with class II–IV outcomes. There is a tendency for the total ablation volume to be larger in patients with class I outcome than in those with class II–IV outcomes; however, the difference was not statistically significant (P=0.24). Similarly, the per cent of AHC ablated was not significantly different between patients with a class I outcome (69.3%±28.0%) and those with class II–IV outcomes (55.5%±22.9%) (P=0.24). Inter-rater kappa statistics for the volumetry assessment showed a k of 0.84 indicating excellent agreement.

    Postoperative supervised reduction of at least one AED was conducted in 7 (patients 2, 3, 4, 5, 7, 10 and 11) of the 21 patients. Of these patients, three (patients 3, 7 and 10) remained seizure-free; two (patients 4 and 11) had recurrent seizures and regained seizure freedom after resuming the AED; the remaining two patients (patients 2 and 5) continued to have recurrent disabling seizures after resuming the AEDs. Of those who failed LITT, three patients (patients 5, 6 and 12) underwent a repeat LITT and one (patient 5) became seizure-free. The remaining two failed to achieve freedom from disabling seizures. One patient (patient 13) underwent ATL and continued to have disabling seizures.

    Figure 2
    Figure 2

    Kaplan-Meier curve illustrating the proportion of patients achieved complete seizure freedom after MRI-guided LITT of mesial temporal lobe in patients with MTS (blue curve), all patients (black curve) and patient without MTS (red curve) (A). Histogram illustrating seizure outcomes based Engel’s Classification for patients with at least 12 months of follow-up (B). LITT, laser interstitial thermal therapy; MTS, mesial temporal sclerosis.

    Nineteen of 21 patients were discharged within 24 hours of postablation and the remaining 2 patients were discharged 2–4 days after ablation due to dizziness, unsteady gait (patient 19) and visual field deficit (patient 8). A major surgical complication occurred in one patient who developed a homonymous hemianopia due to thermal injury to the lateral geniculate nucleus (LGN), as it was confirmed by diffusion tensor imaging (DTI) tractography.29 The patient also suffered from neurofibromatosis type I and had significant oedema around the lesion after the ablation. One patient (patient 17) developed acute postoperative psychiatric symptoms including anxiety, insomnia, depression; auditory hallucination and suicidal ideation 2 weeks postoperation. He was subsequently admitted for psychiatric care and his symptoms resolved in the following 3 months.

    Neurocognitive outcomes

    Of the 22 patients enrolled, 10 completed both presurgical and postsurgical neuropsychological assessments. Baseline neurological assessment was performed 8±11.5 months before the procedure and postoperative performance was assessed 8±2.8 months. Seven of the 10 patients were operated on the dominant hemisphere and three on the non-dominant hemisphere. One patient in the dominant group failed to complete the WMS subtest due to a time constraint.

    There were no statistically significant group differences across any of the cognitive raw scores post ablation compared with baseline test scores. Using the 90th percentile RCI cut-off ranges, two of the dominant hemisphere patients demonstrated declines on the CVLT delayed free recall trial. On the story memory trial, one person in each hemispheric group declined on the immediate free recall trial and on the delayed free recall trial. Finally, two in the dominant hemisphere group declined on the naming task postablation (table 2). Inspection at the individual level revealed increased rates (>1 SD) of learning problems (WMS-LMI) and delayed free recall problems (CVLTII) following ablation (figure 3).

    View this table:
    Table 2

    Verbal memory and confrontational naming

    Figure 3
    Figure 3

    Percent of patients with dominant and non-dominant ablation showing neurocognitive deficits (>1 SD) prior to and following surgery. BNT, Boston Naming Test (n=10; 7 dominant, 3 non-dominant); CVLT-II, California Verbal Learning Test-Version II (n=10; 7 dominant, 3 non-dominant); WMS-IV LM, The Wechsler Memory Scale-Fourth Version Logical Memory (n=9; 6 dominant, 3 non-dominant).

    Discussion

    Our study demonstrated that 52% of 21 patients with mTLE became free of disabling seizures after LITT with a mean follow-up duration of 24±11 (range: 7–43) months. Meanwhile, 8 (73%) of 11 patients with MTS and 3 (30%) of 10 patients without MTS achieved freedom from disabling seizures. Patients with MTS were significantly more likely to become seizure-free after LITT as compared with those without MTS (P=0.002). These findings are in line with the seizure outcomes in recent studies of LITT for patients with mTLE.14 15 25 30 A mini-review of these studies showed that class I outcome was achieved in 17 (61%) of 28 patients in patients with MTS, whereas it was achieved in 1 (17%) of 6 patients without MTS.31 In the most recently published study which was not included in the mini-review, class I outcome was achieved in 11 (73%) of 15 patients with MTS and in 5 (62%) of 8 patients without MTS. There was no statistical difference of class I outcome in patients with MTS and without MTS.25 When combining all the published cases including those in the current study, class I seizure outcome was achieved in 36 (67%) of 54 patients with MTS and 9 (38%) of 24 patients without MTS. In the systematic review and meta-analysis of standard temporal lobectomy versus SAH, Engel class I seizure outcome was achieved in 381 (68%) of 557 patients with MTS and in 11 (42%) of 26 patients without MTS after SAH.25 32 Standard ATL had an 8% higher chance of achieving freedom from disabling seizures than SAH.32 Therefore, LITT might be able to achieve a seizure-free rate comparable to SAH and modestly reduced seizure-freedom rate compared with ATL.

    Eleven of the 21 patients had unprovoked postoperative seizures in this study. All these patients had their seizures within the first postoperative year and seizures in nine patients occurred within the first 6 months. Two patients had recurrent seizures after 12 months on medication withdrawal. The pattern of seizure recurrence is similar to those in other studies.14 15 30 There are several possible causes for the recurrent seizures: (1) inadequate ablation of the AHC due to suboptimal trajectory of laser catheter relative to the curved structure of the hippocampus; (2) too few ablations or low ablation power relative to heat dissipated by convection via blood vessels and ventricles; (3) an expanded epileptogenic zone that includes structures outside the mesial temporal lobe, including neocortical temporal or extratemporal cortex and (4) bilateral temporal seizure onset. The early postoperative recurrent seizures likely reflected inadequate ablation of the epileptogenic zone, rather than de novo epileptogenesis,33 34 as reflected by a recent finding that sparing the hippocampal head was significantly correlated with persistent disabling seizures. In addition, repeat LITT or ATL have been effective in achieving seizure freedom in patients who failed initial LITT. Nevertheless, our study and other studies did not show a significant difference of the amount of total ablated volume or individual volumes of the ablated mesial temporal structures between seizure-free and non-seizure-free patients after thermal ablation of AHC, although this study is underpowered to detect a statistically significant difference in the mean volume. The impact of total ablation volume and the percentage of ablated AHC on the seizure outcome needs to be further determined in a larger cohort study with sufficient power.

    Given the limited ablation volume in patients who underwent LITT, it is critical to precisely define the epileptogenic zone and completely ablate it in order to achieve the seizure freedom. Laser ablation performed without invasive EEG recordings may raise the concern that the epileptogenic zone may not be adequately removed. In this study, invasive EEG recording was performed in 19 of 21 patients due to the aforementioned concerns for temporal neocortical, extratemporal and bitemporal seizure onsets. SEEG recording from depth electrodes implanted along the longitudinal axis of the AHC through an occipital approach was able to define IOZ in the AHC in all 19 patients. Additionally, 2 of the 19 patients underwent invasive EEG study had seizure onset involving AHC extending into the ipsilateral anterior temporal tip. Both patients underwent the ablation of AHC and ipsilateral anterior temporal tip and have remained seizure-free. Electrical stimulation of depth electrodes was also useful for mapping the visual pathway and reducing the risk of postoperative visual field deficits. Therefore, invasive EEG might be helpful for improving surgical outcomes for minimally invasive epilepsy surgery. Nevertheless, our surgical outcomes fall into the similar range as reported by others.14 15 The value of invasive EEG studies remain to be further determined in large case series.

    Surgical complications of LITT have been reported in patients with mTLE, including visual field defects, haemorrhage and infection. Visual field deficits have been the most common surgical complication.31 MRI-guided stereotactic LITT was well tolerated by the patients in our study. The only major surgical complication was a homonymous hemianopsia, which has been also reported in previous studies.15 25 In a small case series of seven patients, two had partial visual field deficits, although the aetiology and extent of these deficits were not reported.30 In a series of 20 patients, 1 patient experienced a haematoma near the ablation region that resulted in a superior quadrantanopsia, while another patient had transient fourth nerve palsy.14 Delineating visual pathways with preoperative fMRI and DTI tractography may be helpful in mitigating the risk of visual field deficits.

    Neurocognitive impairments after standard ATL are well described.35 36 Dominant hemispheric resection is often associated with cognitive declines in naming and verbal learning, while non-dominant hemispheric resection is associated with impaired nonverbal memory, object recognition and figural learning.37 SAH may provide better neurocognitive outcomes than ATL.38 Recent studies suggest that LITT may also provide superior neurocognitive outcomes over ATL and SAH, particularly in the cognitive domains of naming famous faces and logical memory.12 14 In this study, a significant decline in verbal memory and confrontational naming was observed in individual patients. One of the two patients with a decline in naming had the surgical complication of right homonymous hemianopsia. Although these neurocognitive outcomes are in a small number of patients, the risks of neurocognitive impairments associated with LITT cannot be discounted and needs to be further studied for comparison to the risks associated with SAH and ATL.

    In summary, our study demonstrated that LITT is a safe and effective treatment for patients with mTLE. LITT might be able to replace SAH for removing AHC without the risks of craniotomy and collateral damage to temporal neocortex. LITT might be a reasonable alternative to ATL due to its tolerability, reduced incidence of major complications, shorter recovery time and decreased pain, although with a moderately reduced seizure-freedom rate. The selection of optimal candidates for LITT is of paramount importance to achieve freedom from disabling seizures. Patients with unilateral MTS and infrequent scalp interictal spikes, a special subgroup considered to have a less severe form of TLE, might be the ideal candidates for LITT.16 Nevertheless, the benefit of LITT in patients with non-lesional mTLE remains to be determined and require more physiological and biological targeting. Future multicentre prospective studies are warranted to further characterise both seizure and cognitive outcomes of LITT for patients with mTLE, which is currently under way with the prospective multicentre SLATE (Stereotactic laser Ablation in temporal Epilepsy) trial in USA.

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    Footnotes

    • JXT and SW contributed equally.

    • Contributors JXT, SW and PCW: study design, data analysis and manuscript writing. ML and KED: neurocognitive tests, data analysis and manuscript writing. SR, NPI, MB, JK and AD: data collection and analysis. JC: volumetric data analysis. CWY: brain MRI imaging analysis. VLT: electrode reconstruction.

    • Competing interests None declared.

    • Patient consent Obtained.

    • Ethics approval The University of Chicago Institutional Review Board (IRB, equivalent to local ethics committee) approved this study and a written consent was obtained in all studied patients.

    • Provenance and peer review Not commissioned; externally peer reviewed.