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Background: Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive procedure that utilizes intraoperative magnetic resonance thermal imaging (MRTI) to generate a thermal damage estimate (TDE) of the ablative area. In select cases, the MRTI contains a signal artifact or defect that distorts the ablative region. No study has attempted to characterize this artifact., Objective: To characterize MRTI signal the artifact in select cases to better understand its potential relevance and impact on the ablation procedure., Methods: All ablations were performed using the Visualase magnetic resonance imaging-guided laser ablation system (Medtronic). Patients were included if the MRTI contained signal artifact that distorted the ablative region during the first thermal dose delivered. Ablation artifact was quantified using MATLAB version R2018a (Mathworks Inc, Natick, Massachusetts)., Results: A total of 116 patients undergoing MRgLITT for various surgical indications were examined. MRTI artifact was observed in 37.0% of cases overall. Incidence of artifact was greater at higher powers (P < .001) and with longer ablation times (P = .024), though artifact size did not correlate with laser power or ablation duration., Conclusion: MRTI signal artifact is common during LITT. Higher powers and longer ablation times result in greater incidence of ablation artifact, though artifact size is not correlated with power or duration. Future studies should aim to evaluate effects of artifact on postoperative imaging and, most notably, patient outcomes., (Copyright © 2020 by the Congress of Neurological Surgeons.)

Background: In patients who have previously undergone maximum radiation for metastatic brain tumors, a progressive enhancing inflammatory reaction (PEIR) that represents either tumor recurrence or radiation necrosis, or a combination of both, can occur. Magnetic resonance-guided laser-induced thermal therapy (LITT) offers a minimally invasive treatment option for this problem., Objective: To report our single-center experience using LITT to treat PEIRs after radiosurgery for brain metastases., Methods: Patients with progressive, enhancing reactions at the site of prior radiosurgery for metastatic brain tumors and who had a Karnofsky performance status of ≥70 were eligible for LITT. The primary endpoint was local control. Secondary end points included dexamethasone use and procedure-related complications., Results: Between 2010 and 2017, 59 patients who underwent 74 LITT procedures for 74 PEIRs met inclusion criteria. The mean pre-LITT PEIR size measured 3.4 ± 0.4 cm3. At a median follow-up of 44.6 wk post-LITT, the local control rate was 83.1%. Most patients were weaned off steroids post-LITT. Patients experiencing a post-LITT complication were more likely to remain on steroids indefinitely. The rate of new permanent neurological deficit was 3.4%., Conclusion: LITT is an effective treatment for local control of PEIRs after radiosurgery for metastatic brain disease. When possible, we recommend offering LITT once PEIRs are identified and prior to the initiation of high-dose steroids for symptom relief., (Copyright © 2018 by the Congress of Neurological Surgeons.)

Temporal encephalocele (TE) is a rare but surgically treatable/curable cause of temporal lobe epilepsy (TLE). The surgical intervention varies from local disconnection to extensive anterior temporal lobectomy and amygdalohippocampectomy (ATL/AH). Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) has evolved as a minimally invasive alternative for intractable epilepsy with good results, however, application of MRgLITT for intractable pediatric epilepsy secondary to TE has not been reported. We present a detailed technical report and clinical experience of MRgLITT in two adolescent children with medically intractable TLE secondary to TE. Pre-surgical evaluation revealed anterior inferior TE with concordant clinico-electrophysiological data. Both the patients underwent MRgLITT after review with the institutional multidisciplinary epilepsy team and discussion with the patient and the family. Both the patients were discharged on post-operative day one and have been seizure-free since the procedure at the last follow-up visit at 18 months and 6 months, respectively. The present series demonstrates first-ever clinical and technical experience of MRgLITT for TE with intractable pediatric epilepsy. The excellent post-operative seizure outcome and favorable postoperative course support MRgLITT as the first line of surgical intervention for TE with intractable TLE and broadens the application of MRgLITT.

Objective: Intraoperative dynamics of magnetic resonance-guided laser-induced thermal therapy (MRgLITT) have been previously characterized for ablations of naive tissue. However, most treatment sessions require the delivery of multiple doses, and little is known about the ablation dynamics when additional doses are applied to heat-damaged tissue. This study investigated the differences in ablation dynamics between naive versus damaged tissue., Methods: The authors examined 168 ablations from 60 patients across various surgical indications. All ablations were performed using the Visualase MRI-guided laser ablation system (Medtronic), which employs a 980-nm diffusing tip diode laser. Cases with multiple topographically overlapping doses with constant power were selected for this study. Single-dose intraoperative thermal damage was used to calculate ablation rate based on the thermal damage estimate (TDE) of the maximum area of ablation achieved (TDEmax) and the total duration of ablation (tmax). We compared ablation rates of naive undamaged tissue and damaged tissue exposed to subsequent thermal doses following an initial ablation., Results: TDEmax was significantly decreased in subsequent ablations compared to the preceding ablation (initial ablation 227.8 ± 17.7 mm2, second ablation 164.1 ± 21.5 mm2, third ablation 124.3 ± 11.2 mm2; p = < 0.001). The ablation rate of subsequent thermal doses delivered to previously damaged tissue was significantly decreased compared to the ablation rate of naive tissue (initial ablation 2.703 mm2/sec; second ablation 1.559 mm2/sec; third ablation 1.237 mm2/sec; fourth ablation 1.076 mm/sec; p = < 0.001). A negative correlation was found between TDEmax and percentage of overlap in a subsequent ablation with previously damaged tissue (r = -0.164; p < 0.02)., Conclusions: Ablation of previously ablated tissue results in a reduced ablation rate and reduced TDEmax. Additionally, each successive thermal dose in a series of sequential ablations results in a decreased ablation rate relative to that of the preceding ablation. In the absence of a change in power, operators should anticipate a possible reduction in TDE when ablating partially damaged tissue for a similar amount of time compared to the preceding ablation.

OBJECTIVE Magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) is a novel, minimally invasive treatment for the surgical treatment of epilepsy. In this paper, the authors report on clinical outcomes for a series of pediatric patients with tuberous sclerosis complex (TSC) and medication-refractory epileptogenic cortical tubers. METHODS A retrospective chart review was performed at SUNY Upstate Golisano Children's Hospital in Syracuse, New York. The authors included all cases involving pediatric patients (< 18 years) who underwent MRgLITT for ablation of epileptogenic cortical tubers between February 2013 and November 2015. RESULTS Seven patients with cortical tubers were treated (4 female and 3 male). The patients' average age was 6.6 years (range 2-17 years). Two patients had a single procedure, and 5 patients had staged procedures. The mean time between procedures in the staged cases was 6 months. All of the patients had a meaningful reduction in seizure frequency as reported by Engel and ILAE seizure outcome classifications, and most (71.4%) of the patients experienced a reduction in AED burden. Three of the 4 patients who presented with neuropsychiatric symptoms had some improvement in these domains after laser ablation. No perioperative complications were noted. The mean duration of follow-up was 19.3 months (range 4-49 months). CONCLUSIONS Laser ablation represents a minimally invasive alternative to resective epilepsy surgery and is an effective treatment for refractory epilepsy due to cortical tubers.

OBJECTIVE Stereoelectroencephalography (sEEG) and MR-guided laser interstitial thermal therapy (MRgLITT) have both emerged as minimally invasive alternatives to open surgery for the localization and treatment of medically refractory lesional epilepsy. Although some data are available about the use of these procedures individually, reports are almost nonexistent on their use in conjunction. The authors' aim was to report early outcomes regarding efficacy and safety of sEEG followed by MRgLITT for localization and ablation of seizure foci in the pediatric population with medically refractory lesional epilepsy. METHODS A single-center retrospective review of pediatric patients who underwent sEEG followed by MRgLITT procedures was performed. Demographic, intraoperative, and outcome data were compiled and analyzed. RESULTS Four pediatric patients with 9 total lesions underwent sEEG followed by MRgLITT procedures between January and September 2017. The mean age at surgery was 10.75 (range 2-21) years. Two patients had tuberous sclerosis and 2 had focal cortical dysplasia. Methods of stereotaxy consisted of BrainLab VarioGuide and ROSA robotic guidance, with successful localization of seizure foci in all cases. The sEEG procedure length averaged 153 (range 67-235) minutes, with a mean of 6 (range 4-8) electrodes and 56 (range 18-84) contacts per patient. The MRgLITT procedure length averaged 223 (range 179-252) minutes. The mean duration of monitoring was 6 (range 4-8) days, and the mean total hospital stay was 8 (range 5-11) days. Over a mean follow-up duration of 9.3 (range 5.1-16) months, 3 patients were seizure free (Engel class I, 75%), and 1 patient saw significant improvement in seizure frequency (Engel class II, 25%). There were no complications. CONCLUSIONS These early data demonstrate that sEEG followed by MRgLITT can be used safely and effectively to localize and ablate epileptogenic foci in a minimally invasive paradigm for treatment of medically refractory lesional epilepsy in pediatric populations. Continued collection of data with extended follow-up is needed.

Background and Objectives: Magnetic-Resonance Guided Laser-Induced Thermal Therapy (MRgLITT) is a minimally-invasive ablation procedure for treating intracranial pathology using laser energy delivered through a fiber-optic. Saline irrigation is used to cool the fiber-optic, but factors affecting irrigation efficacy are not well studied, and quantitative information regarding irrigation speed and volume during MRgLITT procedures have not been reported. Here, we aimed to characterize variables affecting irrigation efficacy in MRgLITT., Methods: We investigated the irrigation setup of the Visualase thermal therapy system during MRgLITT procedures (Visualase Inc., Houston, TX). Using the system's peristaltic pump, irrigation flow rate was quantitated by measuring volume over five one-minute intervals. Pump settings 1-10 were assessed with and without the position-locking, resistance-imparting bone anchor in both single and double-catheter setups. Multiple tightness settings of the bone anchor were tested, and flow rates were analyzed., Results: Rate of flow increased non-linearly with pump setting (F(1,4) = 2168.86; P < 0.001) in both single and double catheter setups. The lowest pump setting had a flow rate of 24 cc/min, while the highest setting was 36 cc/min. The rate of change in flow successively decreased without plateau. Tightness setting of the bone anchor affected flow in a reverse sigmoid pattern, with no impact on rate until after two quarter-turns, which produced a marked decrease in flow up to one-half of the initial rate (F(1,4) = 12818.96; P < 0.001)., Conclusion: Flow rate through the cooling catheter in MRgLITT follows a non-linear pattern with increasing peristaltic pump speed. This rate is subject to significant changes when the bone anchor is tightened more than two quarter-turns. These findings serve as a foundation for future studies aimed at understanding the effect of irrigation speeds in achieving optimal ablation volumes., (© 2015 Wiley Periodicals, Inc.)