Laser ablation for mesial temporal epilepsy: a multi-site, single institutional series

Restricted access

OBJECTIVE

Although it is still early in its application, laser interstitial thermal therapy (LiTT) has increasingly been employed as a surgical option for patients with mesial temporal lobe epilepsy. This study aimed to describe mesial temporal lobe ablation volumes and seizure outcomes following LiTT across the Mayo Clinic’s 3 epilepsy surgery centers.

METHODS

This was a multi-site, single-institution, retrospective review of seizure outcomes and ablation volumes following LiTT for medically intractable mesial temporal lobe epilepsy between October 2011 and October 2015. Pre-ablation and post-ablation follow-up volumes of the hippocampus were measured using FreeSurfer, and the volume of ablated tissue was also measured on intraoperative MRI using a supervised spline-based edge detection algorithm. To determine seizure outcomes, results were compared between those patients who were seizure free and those who continued to experience seizures.

RESULTS

There were 23 patients who underwent mesial temporal LiTT within the study period. Fifteen patients (65%) had left-sided procedures. The median follow-up was 34 months (range 12–70 months). The mean ablation volume was 6888 mm3. Median hippocampal ablation was 65%, with a median amygdala ablation of 43%. At last follow-up, 11 (48%) of these patients were seizure free. There was no correlation between ablation volume and seizure freedom (p = 0.69). There was also no correlation between percent ablation of the amygdala (p = 0.28) or hippocampus (p = 0.82) and seizure outcomes. Twelve patients underwent formal testing with computational visual fields. Visual field changes were seen in 67% of patients who underwent testing. Comparing the 5 patients with clinically noticeable visual field deficits to the rest of the cohort showed no significant difference in ablation volume between those patients with visual field deficits and those without (p = 0.94). There were 11 patients with follow-up neuropsychological testing. Within this group, verbal learning retention was 76% in the patients with left-sided procedures and 89% in those with right-sided procedures.

CONCLUSIONS

In this study, there was no significant correlation between the ablation volume after LiTT and seizure outcomes. Visual field deficits were common in formally tested patients, much as in patients treated with open temporal lobectomy. Further studies are required to determine the role of amygdalohippocampal ablation.

ABBREVIATIONS AVLT = Auditory Verbal Learning Test; BNT = Boston Naming Test; CVLT = California Verbal Learning Test; LiTT = laser interstitial thermal therapy; MPRAGE = magnetization-prepared rapid acquisition gradient echo; MTS = mesial temporal sclerosis.

Article Information

Correspondence Jamie J. Van Gompel: Mayo Clinic, Rochester, MN. vangompel.jamie@mayo.edu.

INCLUDE WHEN CITING Published online July 6, 2018; DOI: 10.3171/2018.2.JNS171873.

Disclosures Dr. Worrell reports direct stock ownership in Cadence Neuroscience and NeuroOne Inc. Dr. Kaufmann reports a consultant relationship with SpineThera.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    A: Axial T1-weighted MPRAGE Gd-enhanced image showing a laser cannula in the hippocampus with a zone of nonenhancing ablated tissue surrounded by a thin rim of contrast enhancement. B: Axial T2-weighted FLAIR image showing the expected peripheral zone of T2 hyperintense signal around the area of ablation. C: Coronal T1-weighted MPRAGE Gd-enhanced image showing a peripheral zone of enhancing tissue with the catheter in the center of the zone of enhancement.

  • View in gallery

    Coronal and axial T1-weighted pre- and post-LiTT MR images showing segmentation of mesial temporal structures with the FreeSurfer program. These images reveal expected postoperative changes after right mesial temporal lobe ablation. Figure is available in color online only.

  • View in gallery

    Mesial temporal volumes measured by FreeSurfer in pre-ablation T1-weighted MPRAGE imaging show lower overall volume on the side undergoing ablation. The majority of patients studied (88%) had a diagnosis of MTS with volume loss and/or hyperintense signal on FLAIR imaging. Box-and-whisker plots show the 25th and 75th quartiles as demarcated by the box, with the range demarcated by the lines above and below. Figure is available in color online only.

  • View in gallery

    Left: Bar graph describing the variance in ablation volume across patients. Right: Quartile box plot describing the median ablation volume as well as the 25th and 75th quartiles, with the lines in the whisker plot showing the 10th and 90th quartiles and the whiskers indicating the full range.

  • View in gallery

    Mesial temporal volume changes following ablation on the ablated side (red), while the non-ablated side volumes remain constant. A: Volume changes pre- (time = 0) and post-ablation as raw (mm3) volumes. A regression line fit to the volume measurements has a slope of −3.03 mm3/day and a y-intercept of 4875 mm3 for the ablated side, while the non-ablated side’s regression has a slope of 0.134 mm3/day and a y-intercept of 5783 mm3. B: Post-ablation measurements normalized to each patient’s pre-ablation volume are plotted. A regression line fit to the normalized measurements has a slope of −4.9 × 10−4 units/day and a y-intercept of 0.948 for the ablated side, while the non-ablated side’s regression has a slope of 5.5 × 10−5 units/day and a y-intercept of 1.01. Figure is available in color online only.

  • View in gallery

    A: Coronal T1-weighted MR image revealing the location of the lateral geniculate nucleus contralateral to the lesion (yellow arrow); post-ablation changes are noted in the area of the ipsilateral lateral genticulate nucleus (red arrow). B: Axial Gd-enhanced T1-weighted MR image revealing thermal damage to the optic radiations as they exit the lateral geniculate nucleus (red arrow). Figure is available in color online only.

References

TrendMD

Metrics

Metrics

All Time Past Year Past 30 Days
Abstract Views 302 302 32
Full Text Views 416 416 11
PDF Downloads 198 198 9
EPUB Downloads 0 0 0

PubMed

Google Scholar