Magnetic Resonance-guided Laser Interstitial Thermal Therapy Research Articles

Impact of Previous Surgery on Success of Magnetic Resonance-guided Laser Interstitial Thermal Therapy (MRgLITT) to Treat Pediatric Epilepsy: An Institutional Experience

There is an emerging role for minimally invasive magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) in the treatment of pediatric epilepsy refractory to medication. To date, predictors of MRgLITT success have not been established in a sizeable singular experience. Correspondingly the aim of this study was to elucidate if previous surgical history predicts MRgLITT success in this setting. A retrospective review was conducted of our MRgLITT procedures for pediatric (aged <19 years) epilepsy from 2011-2020 with documented seizure outcomes at 1- and 2-years after procedure. Categorical and continuous data were compared using Chi-squared and student's t-test respectively. A total of 41 patients satisfied all criteria with 16 (39%) females and 25 (61%) males. Following MRgLITT, seizure-freedom at 1-year was achieved in 15 (37%) patients. In the cohort, there were 14 (34%) patients who had undergone previous open surgery for epilepsy at mean age of 9.4 ± 5.5 years. Patients with a previous open surgery history were found to statistically experience longer length of hospitalization after MRgLITT (P=0.04) with a statistically lower proportion of seizure-freedom at 1-year after MRgLITT (14% vs 48%, P=0.03). However, there was no difference in the rate of seizure-freedom at 2-years (29% vs 41%, P=0.44), as well as no difference in subsequent surgical interventions for seizure management between groups. Based on our institutional experience, patients with previous open surgery history may experience longer length of hospitalization after MRgLITT for pediatric epilepsy and lesser response in seizure-freedom within the first year but with non-inferior seizure-freedom by the second year.

The changing landscape of palliative epilepsy surgery for Lennox Gastaut Syndrome.

Lennox Gastaut Syndrome (LGS) is characterized by drug-resistant epilepsy that typically leads to decreased quality of life and deleterious neurodevelopmental comorbidities from medically refractory seizures. In recent years there has been a dramatic increase in the development and availability of novel treatment strategies for Lennox Gastaut Syndrome patient to improve seizure. Recent advances in neuromodulation and minimally invasive magnetic resonance guided laser interstitial thermal therapy (MRgLITT) have paved the way for new treatments strategies including deep brain stimulation (DBS), responsive neurostimulation (RNS), and MRgLITT corpus callosum ablation. These new strategies offer hope for children with drug-resistant generalized epilepsies, but important questions remain about the safety and effectiveness of these new approaches. In this review, we describe the opportunities presented by these new strategies and how each treatment strategy is currently being employed. Next, we will critically assess available evidence for these new approaches compared to traditional palliative epilepsy surgery approaches, such as vagus nerve stimulation (VNS) and open microsurgical corpus callosotomy (CC). Finally, we will describe future directions that would help define which of the available strategies should be employed and when.

Negative MRI and a seizure onset zone close to eloquent areas in FCD type II: Application of MRg-LiTT after a SEEG re-evaluation in pediatric patients with a previous failed surgery

ObjectiveNegative MRI and an epileptogenic zone (EZ) adjacent to eloquent areas are two main issues that can be encountered during pre-surgical evaluation for epilepsy surgery. Focal Cortical Dysplasia type II (FCD type II) is the most common aetiology underlying a negative MRI.The objective of this study is to present three cases of pediatric patients exhibiting negative MRI and a seizure onset zone close to eloquent areas, who previously underwent traditional open surgery or SEEG-guided radiofrequency thermocoagulations (RF-TC). After seizure seizure recrudescence, pre-surgical SEEG was re-evaluated and Magnetic Resonance-guided laser interstitial thermal therapy (MRg-LiTT) was performed.We discuss the SEEG patterns, the planning of laser probes trajectories and the outcomes one year after the procedure. MethodsPediatric patients who underwent SEEG followed by MRg-LiTT for drug-resistant epilepsy associated with FCD type II at our Centre were included. Pre-surgical videoEEG (vEEG), stereoEEG (sEEG), and MRI were reviewed. Post-procedure clinical outcome (measured by Engel score) and complications rates were evaluated. ResultsThree patients underwent 3 MRg-LiTT procedures from January 2022 to June 2022. Epileptogenic zone was previously studied via SEEG in all the patients. All the three patients pre-surgical MRI was deemed negative. Mean age at seizure onset was 47 months (21–96 months), mean age at MRg-LiTT was 12 years (10 years 10 months – 12 years 9 months). Engel class Ia outcome was achieved in patients #2 and #3, Engel class Ib in patient #1. Mean follow-up length was of 17 months (13 months – 20 months). Complications occurred in one patient (patient #2, extradural hematoma). ConclusionsThe combined use of SEEG and MRg-LiTT in complex cases can lead to good outcomes both as a rescue therapy after failed surgery, but also as an alternative to open surgery after a successful SEEG-guided Radiofrequency Thermocoagulation (RF-TC). Specific SEEG patterns and a previous good outcome from RF-TC can be predictors of a favourable outcome.

A - 11 Cognitive and Clinical Correlates of Olfactory Function in Adults with Epilepsy.

Olfactory dysfunction is well-documented in epilepsy. We recently found that olfactory assessment may have clinical utility in identifying surgical candidates with intractable epilepsy who benefit from magnetic resonance-guided laser interstitial thermal therapy (MRgLiTT). However, the demographic, clinical, and cognitive correlates of olfaction in epilepsy remain unclear and could aid in understanding its potential utility in clinical examinations. We identified 60 outpatients with epilepsy (mean age = 38.22 ± 13.84years; 50% male; 89.3% right-handed; seizure location: 45.0% left, 33.3% right, 13.3% bilateral, 8.3% unspecified) referred for neuropsychological evaluation in the Johns Hopkins Division of Medical Psychology Clinic. Neuropsychological evaluation included the 16-item Sniffin' Sticks Odor Identification Test. Linear regression models were used to examine associations between 1) olfaction and demographic/clinical characteristics (age, sex, education, duration of illness, seizure laterality) and 2) olfaction and cognition (processing speed, language, auditory-verbal and visuospatial memory, executive functioning; adjusted for demographic/clinical characteristics). Olfactory performance was not significantly associated with demographic or clinical characteristics. Across all participants, better olfactory performance was associated with better auditory-verbal memory (B = 5.04, t(46) = 4.16, p < 0.001) and visual confrontation naming (B = 1.53, t(45) = 4.11, p < 0.001) with correction for multiple comparisons. In a subset with lateralizing epilepsy (n = 47), better odor identification performance remained a significant predictor of the aforementioned cognitive measures with adjustment for demographic and clinical characteristics. Consistent with work in other neurologic conditions, our preliminary findings indicate that olfactory function is associated with verbally-mediated neuropsychological measures in epilepsy. Future studies utilizing pre-surgical neuroimaging will examine the association between olfaction, cognition, and radiographic markers of tissue integrity in epilepsy.

Correlating Thermodynamics with Cognitive Outcomes in Magnetic Resonance-guided Laser Interstitial Thermal Therapy (MRgLITT) of a Pediatric Hypothalamic Hamartoma

Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a commonly used clinical method of destroying intracranial brain foci. Our objective was to correlate the thermal damage estimate transition zone with cognitive outcomes in MRgLITT of a pediatric hypothalamic hamartoma. Uncomplicated MRgLITT was used to disconnect an 8-mm left Delalande grade II hypothalamic hamartoma (HH) revealed on neuroimaging of a 17-year-old male patient with drug-resistant epilepsy and a "gelastic+" semiology including both gelastic and tonic-clonic seizures. Despite meticulous planning, submillimetric stereotactic accuracy, and reassuring intraoperative thermography, the patient experienced transient, but profound, global amnesia. Retroactively, we applied a new iteration of thermographic software that overlays a magenta-colored transition zone (TZ) around the necrotic zone defined by the orange-pigmented thermal damage estimate (TDE). Clear involvement of the bilateral mesial circuits was demonstrated by the overlay of the TZ on the TDE. Involvement of the bilateral mesial circuits visualized with TDE and TZ could account for the neurocognitive outcomes of our patient. We highlight this case as our understanding of thermography analysis evolves, emphasizing principles of technique and trajectory planning, as well as considerations during thermablation to help inform surgical decision-making.

151 Intracranial Magnetic Resonance Guided Laser Interstitial Thermal Therapy for Epilepsy: A Single Institution’s Experience of 226 Cases

INTRODUCTION: Magnetic resonance guided laser interstitial thermal therapy (MRg-LITT) is a minimally invasive alternative to open surgical resection for epilepsy. Patient and technical factors associated with outcomes remain unclear. METHODS: We performed a retrospective review of consecutive patients undergoing MRg-LITT surgery at a single high-volume epilepsy center. Medical and surgical history, trajectory number per patient, adverse events, and outcomes up to 24 months were obtained and statistically analyzed. RESULTS: 203 patients underwent a total of 226 MRg-LITT procedures for epilepsy between 2011-2020. 52% and 55% of patients experienced seizure freedom at 12 and 24 months after ablation, respectively. Overall, patients with lesional epileptogenic foci were more likely to have better seizure control at 12- and 24-months after surgery (p &lt; 0.05). Of cases performed with curative intent, patients with mesial temporal sclerosis (MTS) were most likely to maintain long-term seizure freedom. Ablations performed for disconnection (corpus callosotomy) or palliation of multifocal epilepsy were unlikely to provide complete seizure freedom. 6 cases (2.7%) were complicated by intra- or post-operative hemorrhage. 3 patients (1.5%) experienced persistent post-operative complaints including cranial nerve palsy and headaches. The odds of complication (minor or major vs none) were multiplied by 1.43 for each additional trajectory (95% CI [1.16, 1.76]), and by 1.04 for each additional 1cm3 of volume ablated (95% CI [1.008, 1.076]). CONCLUSIONS: MRg-LITT, a safe and effective approach to distinct epilepsy types, appears most persistently beneficial for lesional epilepsy, particularly MTS. Although serious complications were infrequent, adverse events were statistically correlated with multiple stereotaxic trajectories and larger ablation volumes. Our results provide additional guidance for patient counseling and surgical planning.

Appearance and modeling of bubble artifacts in intracranial magnetic resonance-guided laser interstitial thermal therapy (MRg-LITT) temperature images

PurposeTo understand if unexplained signal artifacts in MRg-LITT proton resonance frequency- (PRF-) shift thermometry images are caused by air bubbles or hemorrhages, and to characterize their effects on temperature measurements. MethodsRetrospective image data from an IRB-approved clinical trial of intracranial MRg-LITT were inspected for asymmetric distortions observed in phase data during ablations, which have been previously reported as likely hemorrhages. A total of eight patient cases were selected: seven with artifact occurrence and one without. Mathematical image models for air bubbles or hemorrhages were implemented to estimate the size of the air bubble or hemorrhage needed to explain the clinically observed phase artifacts. Correlations and Bland-Altman analyses were used to determine if an air bubble model or a hemorrhage model was better correlated to the clinical data. The model was used to inject bubbles into clean PRF phase data without artifacts to examine how temperature profile distortions change with slice orientation. The simulated air-bubble injected data were compared to clinical data containing artifacts to examine the bubbles' effects on temperature and thermal damage estimates. ResultsThe model demonstrated that air bubbles up to approximately 1 cm in diameter could explain the clinically observed phase artifacts. The bubble model predicts that a hemorrhage would have to be 2.2 times as large as an air bubble in order to explain the same extent of phase distortion observed in clinical data. Air bubbles had 16% percent higher correlations to the clinical PRF phase data than hemorrhages, even after rescaling the hemorrhage phases to better match the data. The air bubble model also explains how the phase artifacts lead to both large positive and large negative temperature errors, up to ±100 °C, which could cascade to damage estimate errors of several millimeters. ConclusionResults showed that the artifacts are likely caused by air bubbles rather than hemorrhages, which may be introduced before heating or appear during heating. Manufacturers and users of devices that rely upon PRF-shift thermometry should be aware these phase distortions from bubble artifacts can result in large temperature errors.

Single-Institution Comparative Study of Magnetic Resonance–Guided Laser Interstitial Thermal Therapy and Open Corpus Callosotomy

Open corpus callosotomy (CC) poses a higher risk of perioperative morbidity than does magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) for treatment of drop and generalized seizures without documented superiority. We present a single-institution comparison between open and MRgLITT CC. A 2-year retrospective review was performed of patients who underwent open and MRgLITT CC (January 2019-January 2021). Demographics, surgical outcome data, hospital costs, and interhemispheric connectivity with diffusion tensor imaging were compared. The average age in years was 9.3 and 11.4 for CC (n= 4) and MRgLITT (n= 9), respectively. Preoperative drop seizure frequency was higher in CC (25 vs. 14.5 seizures/day; P= 0.59). At 10 months follow-up, the reduction in drop seizure frequency was better in open CC, but not statistically significant (93.8% vs. 64.3%; P= 0.21). The extent of CC ablation did not correlate with seizure reduction (Pearson coefficient= 0.09). An inverse correlation between interhemispheric connectivity change (diffusion tensor imaging analysis) and drop seizure frequency reduction was noted (Pearson coefficient= -0.97). Total hospital cost was significantly lower in MRgLITT ($67,754 vs. $107,111; P= 0.004), attributed to lower intensive care unit (1.1 vs. 4 days; P= 0.004) and total hospital stay (1.8 vs. 10.5 days; P= 0.0001). Postoperative hydrocephalus was present in 75% of patients in the CC group compared with zero in the MRgLITT group. Our middle-volume single-institution experience shows the safety, efficacy, and cost-effective benefit of MRgLITT compared with the traditional CC with therapeutic equipoise. This study is limited by the number of patients and, hence, further patient enrollment or multicenter study is warranted.

Insula in epilepsy – “untying the gordian knot”: A systematic review

PurposeDespite significant advances in epileptology, there are still many uncertainties about the role of the insula in epilepsy. Until recently, most insular onset seizures were wrongly attributed to the temporal lobe. Further, there are no standardised approaches to the diagnosis and treatment of insular onset seizures. This systematic review gathers the available information about insular epilepsy and synthesizes current knowledge as a basis for future research. MethodAdhering to the PRISMA guidelines, studies were meticulously extracted from the PubMed database. The empirical data pertaining to the semiology of insular seizures, insular networks in epilepsy, techniques of mapping the insula, and the surgical intricacies of non-lesional insular epilepsy were reviewed from published studies. The corpus of information available was then subjected to a process of concise summarization and astute synthesis. ResultsOut of 235 studies identified for full-text review, 86 studies were included in the systematic review. The insula emerges as a brain region with a number of functional subdivisions. The semiology of insular seizures is diverse and depends on the involvement of particular subdivisions. The semiological heterogeneity of insular seizures is explained by the extensive connectivity of the insula and its subdivisions with all four lobes of the brain, deep grey matter structures, and remote brainstem areas. The mainstay of the diagnosis of seizure onset in the insula is stereoelectroencephalography (SEEG). The surgical resection of the insular epileptogenic zone (when possible) is the most effective treatment. Open surgery on the insula is challenging but magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) also holds promise. ConclusionThe physiological and functional roles of the insula in epilepsy have remained obfuscated. The dearth of precisely defined diagnostic and therapeutic protocols acts as an impediment to scientific advancement. This review could potentially facilitate forthcoming research endeavours by establishing a foundational framework for uniform data collection protocols, thereby enhancing the feasibility of comparing findings across future studies and promoting progress in this domain.

Magnetic Resonance-Guided Laser Interstitial Thermal Therapy for Hypothalamic Hamartoma: Surgical Approach and Treatment Outcomes.

Hypothalamic hamartoma (HH) is a rare lesion consisting of normal neurons and neuroglia arranged in an abnormal pattern which usually causes gelastic seizures (GS). Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has been developed as a minimally invasive approach to treat HH and gradually become a first-line treatment. In total, this study enrolled 47 consecutive HH patients that underwent one round of ablation. Patients were followed for at least one year. Patients' medical records and surgical information were carefully reviewed, and univariate analyses were performed. Of the treated patients, 72.3% remained GS-free in this study, with an overall Engel class I rate of 68.1%. Long-term postoperative complications occurred in six patients. Factors associated with GS prognosis included Delalande classification (p = 0.033), HH volume (p = 0.01), and the ablation rate of the HH body (p = 0.035). The disconnection rate was 0.73 ± 0.14 in the Engel class Ia group as compared to 0.62 ± 0.13 in the Engel Ib-Engel IV group (p = 0.046). MRgLITT represents a safe and effective surgical procedure. Patients with larger or Delalande type IV HH may require multiple rounds of ablation. In addition to assessing the degree of disconnection, ablation volume should also be carefully considered for patients undergoing this procedure.

Association of intraoperative end-tidal carbon dioxide level with ablation volume during magnetic resonance-guided laser interstitial thermal therapy for mesial temporal lobe epilepsy.

Maximal safe ablation of target structures during magnetic resonance-guided laser interstitial thermal therapy (MRgLiTT) is critical to achieving good seizure outcome in patients with mesial temporal lobe epilepsy (mTLE). The authors sought to determine whether intraoperative physiological variables are associated with ablation volume during MRgLiTT. Patients with mTLE who underwent MRgLiTT at our institution from 2014 to 2019 were retrospectively analyzed. Ablation volume was determined with volumetric analysis of intraoperative postablation MR images. Physiological parameters (systolic blood pressure [SBP], diastolic blood pressure [DBP], mean arterial pressure [MAP], end-tidal carbon dioxide [ETCO2]) measured 40 minutes prior to ablation were analyzed. Univariate and multivariate regression analyses were performed to determine independent predictors of ablation volume. Forty-four patients met the inclusion criteria. The median (interquartile range) ablation volume was 4.27 (2.92-5.89) cm3, and median ablation energy was 7216 (6402-8784) J. The median MAP, SBP, DBP, and ETCO2 values measured during the 40-minute period leading up to ablation were 72.8 (66.2-81.5) mm Hg, 104.4 (96.4-114.4) mm Hg, 62.4 (54.1-69.8) mm Hg, and 34.1 (32.0-36.2) mm Hg, respectively. In univariate analysis, only total laser energy (r = 0.464, p = 0.003) and 40-minute average ETCO2 (r = -0.388, p = 0.012) were significantly associated with ablation volume. In multivariate analysis, only ETCO2 ≤ 33 mm Hg (p = 0.001) was significantly associated with ablation volume. Total ablation energy and ETCO2, but not blood pressure, may significantly affect ablation volume in mTLE patients undergoing MRgLiTT. Mild hypocapnia was associated with increased extent of ablation. Intraoperative monitoring and modulation of ETCO2 may help improve extent of ablation, prediction of ablation volume, and potentially seizure outcome.

Magnetic Resonance-Guided Laser Interstitial Thermal Therapy for Brainstem Pathologies

Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive and effective treatment option that can potentially treat deep-seated pathologies in cases without safe open surgical corridors. In the present report, we have described our experience using MRgLITT for brainstem pathologies. A retrospective medical record review and analysis were conducted for all patients who had undergone MRgLITT for pathologies within or closely surrounding the brainstem between 2011 and 2020. The patients had undergone stereotactic laser placement in the operating suite and were transported to the magnetic resonance imaging suite for laser ablation with real-time monitoring. The demographics, operative parameters, and complications were recorded. A total of 12 patients had undergone MRgLITT for brainstem pathologies. The average age of the patients was 47.6 years (range, 4-75 years). The pathologies included both primary and metastatic intracranial tumors. The average preablation volume of the targets was 2.4±0.50 cm3. The average ablation time was 324.3 ± 60.7 seconds, and the average postablation volume was 2.92±0.53 cm3. One perioperative mortality was directly related to the procedure and 7 patients developed postoperative deficits. Two patients had experienced a recurrence after MRgLITT and opted to undergo additional alternative treatment. The brainstem represents formidable territory even for minimally invasive procedures. The overall morbidity and mortality has remained high, and the probability of achieving a meaningful outcome must be carefully assessed.

Magnetic resonance-guided laser interstitial thermal therapy (MR-gLiTT) in pediatric epilepsy surgery: experience at Giannina Gaslini Children’s Hospital (Genoa, Italy)

Magnetic resonance-guided laser interstitial thermal therapy (MR-gLiTT) in pediatric epilepsy surgery: experience at Giannina Gaslini Children’s Hospital (Genoa, Italy)

Controlling Signal Artifact With Software Threshold Imaging for Magnetic Resonance-Guided Laser Interstitial Thermal Therapy.

Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) uses intraoperative temperature mapping and thermal damage estimates to guide ablations of intracranial targets. In select cases, signal artifact presents at the target site and impairs intraprocedural decision-making by obscuring the visualization of both temperature imaging and the thermal damage estimate calculation. To date, the etiology and impact of signal artifact are unknown. However, user-selected MRgLITT software settings may play a role in generating artifact. To assess the effect of the thresholding feature in MRgLITT software on signal artifact generation during intracranial ablations. Ablations were performed with the Visualase MRI-guided Laser Ablation System (Medtronic). For each LITT procedure, raw thermal data were extracted at a reference threshold of 40 and reprocessed at 5 additional threshold values ranging from 35 to 60. Artifact growth rates relative to threshold values were derived using simple linear regressions and then assessed within the context of laser power and duration using Pearson correlations. A total of 33 patients were included, with 28 artifact-containing and 5 artifact-free cases. For artifact-containing cases, a 13% increase in artifact area occurred for every 1-point increase in threshold (R2 > 0.99). Artifact growth rates were not correlated with laser power (r = 0.15, P = .44) or duration (r = 0.0049, P = .98). One of the 5 artifact-free cases developed artifact at a threshold of 60. Artifact generation is likely multifactorial involving tissue properties and software settings. Operators can minimize software-introduced artifact by reducing threshold values.

Magnetic Resonance-Guided Laser Interstitial Thermal Therapy (MR-gLiTT) in Pediatric Epilepsy Surgery: State of the Art and Presentation of Giannina Gaslini Children's Hospital (Genoa, Italy) Series.

Magnetic resonance-guided laser interstitial thermal therapy (MR-gLiTT) is a novel minimally invasive treatment approach for drug-resistant focal epilepsy and brain tumors. Using thermal ablation induced by a laser diode implanted intracranially in a stereotactic manner, the technique is highly effective and safe, reducing the risk associated with more traditional open surgical approaches that could lead to increased neurological morbidity. Indications for MR-gLiTT in pediatric epilepsy surgery include hypothalamic hamartoma, tuberous sclerosis complex, cavernoma-related epilepsy, SEEG-guided seizure onset zone ablation, corpus callosotomy, periventricular nodular heterotopia, mesial temporal lobe epilepsy, and insular epilepsy. We review the available literature on the topic and present our series of patients with drug-resistant epilepsy treated by MR-gLiTT. Our experience, represented by six cases of hypothalamic hamartomas, one case of tuberous sclerosis, and one case of dysembryoplastic neuroepithelial tumor, helps to confirm that MR-gLiTT is a highly safe and effective procedure for several epilepsy conditions in children.

Non-robotized frameless stereotactic magnetic resonance guided laser interstitial thermal therapy for hypothalamic hamartoma.

Various strategies have been proposed for the treatment of gelastic seizures due to hypothalamic hamartomas (HH), advancing from surgical removal techniques toward functional disconnection strategies. One of the most recent procedure is the Magnetic Resonance guided Laser Interstitial Thermal Therapy (MRg-LITT), which has progressively proved to be a safe and effective technique for hamartomas ablation. In this paper, the authors' preliminary experience with the first two patients treated with this technique in Italy is presented, in order to underline the feasibility of a pure non robotized frameless technique (FS MRg-LITT) while confirming the procedure effectiveness on seizure control. Patients undergoing FS MRg-LITT for the treatment of HH related gelastic seizures since January 2020 were included. A two steps procedure was performed by using the neuronavigation system to define the entry point, the trajectories and to assess the accuracy. Visualase Laser Ablation System was then used for the MR guided ablation of the HH. A multidisciplinary (neurosurgeons, epileptologist, neuroradiologist) institutional board evaluated the patients both in the perioperative period and during follow-up. A total number of 2 pediatric patients were described. The mean operative time resulted to be 6 hours while the mean accuracy was 0.4 mm. No perioperative complications were reported. The mean length of stay was 4 days. Lastly, at 1-year follow-up both patients resulted to be seizure free and endocrinological functions were preserved. FS MRg-LITT for the treatment of HH-related epilepsy could represent an effective technique, being able to guarantee adequate level of accuracy and potentially extending the accessibility of MRg-LITT by lowering its costs and simplifying the overall procedure.

Does the Modified Arrhenius Model Reliably Predict Area of Tissue Ablation After Magnetic Resonance-Guided Laser Interstitial Thermal Therapy for Pediatric Lesional Epilepsy?

Commercial magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) systems utilize a generalized Arrhenius model to estimate the area of tissue damage based on the power and time of ablation. However, the reliability of these estimates in Vivo remains unclear. To determine the accuracy and precision of the thermal damage estimate (TDE) calculated by commercially available MRgLITT systems using the generalized Arrhenius model. A single-center retrospective review of pediatric patients undergoing MRgLITT for lesional epilepsy was performed. The area of each lesion was measured on both TDE and intraoperative postablation, postcontrast T1 magnetic resonance images using ImageJ. Lesions requiring multiple ablations were excluded. The strength of the correlation between TDE and postlesioning measurements was assessed via linear regression. A total of 32 lesions were identified in 19 patients. After exclusion, 13 pairs were available for analysis. Linear regression demonstrated a strong correlation between estimated and actual ablation areas (R2=.97, P<.00001). The TDE underestimated the area of ablation by an average of 3.92% overall (standard error (SE)=4.57%), but this varied depending on the type of pathologic tissue involved. TDE accuracy and precision were highest in tubers (n=3), with average underestimation of 2.33% (SE=0.33%). TDE underestimated the lesioning of the single hypothalamic hamartoma in our series by 52%. In periventricular nodular heterotopias, TDE overestimated ablation areas by an average of 13% (n=2). TDE reliability is variably consistent across tissue types, particularly in smaller or periventricular lesions. Further investigation is needed to understand the accuracy of this emerging minimally invasive technique.

Magnetic resonance-guided laser interstitial thermal therapy: Correlations with seizure outcome.

This study was undertaken to identify clinical factors associated with seizure freedom after magnetic resonance-guided laser interstitial thermal therapy (MRgLiTT) in temporal lobe epilepsy patients with unilateral mesial temporal sclerosis (MTS). We identified 56 patients with magnetic resonance imaging-defined MTS who underwent MRgLiTT with at least 1year of follow-up. Primary outcome was seizure freedom at 1 year. We examined the association of seizure freedom and the following clinical factors: age at surgery, gender, history of febrile seizures, history of focal to bilateral tonic-clonic seizures, duration of epilepsy at the time of surgery, frequency of interictal epileptiform discharges (IEDs), seizure frequency, and presence of bilateral IEDs. Thirty-five (62.5%) patients were seizure-free at 1year. The presence of bilateral IEDs and age at surgery were associated with 1-year seizure freedom after MRgLiTT. The presence of bilateral IEDS was associated with lower odds of seizure freedom (odds ratio [OR] = .05, 95% confidence interval [CI] = .01-.46, p=.008), whereas increasing age at surgery was associated with increased odds of seizure freedom (OR = 1.10, 95% CI = 1.03-1.19, p=.009). This study demonstrates associations between presence of bilateral IEDs and age at surgery and seizure freedom at 1year after MRgLiTT.

Surgical targeting of large hypothalamic hamartomas and seizure-freedom following MR-guided laser interstitial thermal therapy

BackgroundLarge hypothalamic hamartomas (HH) are often associated with difficult-to-treat, refractory seizures. Although magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has emerged as a useful tool to treat these challenging lesions, postoperative outcomes are variable and potentially related to differences in surgical targeting. PurposeWe sought to identify differences in the anatomic localization of laser ablations that either did or did not result in seizure freedom. MethodsFour children who underwent MRgLITT for large HH (3 seizure-free and 1 not seizure-free) were included in the analysis. Ablation volumes were segmented, normalized, and overlaid on a high-resolution hypothalamic atlas. For each lesion, the size, spatial extent, and degree of overlap with key hypothalamic nuclei and surrounding brain regions were computed and compared between ablations that did and did not result in seizure freedom. ResultsAblation masks that resulted in seizure freedom were smaller and located more centrally than the ablation mask that did not. In addition, ablation masks that resulted in seizure freedom overlapped with regions including the paraventricular nucleus, the posterior hypothalamus and the zona incerta, fornix, and mammillothalamic tract, whereas the single non-seizure-free ablation did not. ConclusionDifferences in the size, position, and anatomical localization of ablation volumes may be a potential contributor to the variability in postoperative outcomes of large HH treated with MRgLITT. A novel, high-resolution MRI atlas of the hypothalamus identifies a number of regions at the interface of large HH that are preferentially disconnected in seizure-free patients. This method of anatomical localization not only serves as a potential clinical tool for surgical targeting but may also provide novel insights into the mechanisms of epileptogenesis in hypothalamic hamartomas.

Mathematical Modeling of Thermal Damage Estimate Volumes in MR-guided Laser Interstitial Thermal Therapy.

Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive procedure that produces real-time thermal damage estimates (TDEs) of ablation. Currently, MRgLITT software provides limited quantitative parameters for intraoperative monitoring, but orthogonal TDE-MRI slices can be utilized to mathematically estimate ablation volume. The objective of this study was to model TDE volumes and validate using post-24 hours MRI ablative volumes. Ablations were performed with the Visualase Laser Ablation System (Medtronic). Using ellipsoidal parameters determined for dual-TDEs from orthogonal MRI planes, TDE volumes were calculated by two definite integral methods (A and B) implemented in Matlab (MathWorks). Post-24 hours MRI ablative volumes were measured in OsiriX (Pixmeo) by two-blinded raters and compared to TDE volumes via paired t-test and Pearson's correlations. Twenty-two ablations for 20 patients with various intracranial pathologies were included. Average TDE volume calculated with method A was 3.44 ± 1.96 cm3 and with method B was 4.83 ± 1.53 cm3 . Method A TDE volumes were significantly different than post-24 hours volumes (P < .001). Method B TDE volumes were not significantly different than post-24 hours volumes (P = .39) and strongly correlated with each other (r = .85, R2 = .72, P < .0001). A total of eight of 22 (36%) method A versus 17 of 22 (77%) method B TDE volumes were within 25% of the post-24 hours ablative volume. We present a viable mathematical method integrating dual-plane TDEs to calculate volumes. Future algorithmic iterations will incorporate additional calculated variables that improve ablative volume estimations.