Article
Anterior nucleus of the thalamus (ANT) stimulation in epilepsy: stereotactic targeting and localization of effective contacts
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Authors
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Johannes A. Köppen
- Klinik für Neurochirurgie, Universitätsklinikum Hamburg-Eppendorf, Hamburg
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Fahimeh Nahravani
- Klinik für Neurochirurgie, Universitätsklinikum Hamburg-Eppendorf, Hamburg
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Christian K. E. Moll
- Institut für Neurophysiologie und Pathophysiologie, Universitätsklinikum Hamburg-Eppendorf, Hamburg
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Martin Kramer
- Fachbereich Veterinärmedizin, Justus- Liebig Universität Giessen, Giessen
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Berthold Voges
- Epilepsiezentrum Hamburg, Ev. Krankenhaus Alsterdorf, Hamburg
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Manfred Westphal
- Klinik für Neurochirurgie, Universitätsklinikum Hamburg-Eppendorf, Hamburg
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Wolfgang Hamel
- Klinik für Neurochirurgie, Universitätsklinikum Hamburg-Eppendorf, Hamburg
| Published: | June 2, 2015 |
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Outline
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Objective: Both the surgical approach and the optimal site for deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) for epilepsy are controversial.
Method: An extraventricular approach was used for bilateral electrode implantation in general anaesthesia in 14 patients (10 female; median age 35). Electrode implantation was guided by the mammillothalamic tract and involved microelectrode recordings. The stereotactic position of active contacts was determined from intraoperative computed tomography. An open source-based stereotactic software tool was developed to analyze the position of electrode contacts with respect to the mammillothalamic tract and thalamic nuclei. To this end, both structures had been individually segmented from preoperative MRI using a free application (ITKSnap).
Results: For 11 patients, mean and median follow-up was 20 months. Three patients were not analized as follow-up was <6 months. In five patients, partial seizures were reduced by >75% and, in four patients, from 50 to 75%. Secondary generalization was reduced to at least the same extent. Two patients were rated as non-responders (seizure reduction <30%). Intracranial hemorrhages or infections were not observed. Microelectrode recordings revealed abundant bursting activity upon entering the thalamus followed by a silent segment of approximately 2 mm and the recurrence of sparse neuronal activity. The silent region was supposed to represent the transition from the thalamus to fiber structures, i.e. the mammillothalamic tract and/or the internal medullary lamina. In segmented images the course of the mammillothalamic tract and the outer boundary of the thalamus revealed a significant degree of individual as well as interhemispheric variation. Permanent stimulation was performed with contacts located in proximity to the mammillothalamic tract, and several of these were located below the ANT proper. The efficacy of several contacts was substantiated by the fact that the stimulation amplitude could be lowered over time resulting in even improved seizure suppression.
Conclusions: Extraventricular targeting of the mammillothalamic tract represents a safe and effective approach for 'ANT stimulation'. According to analysis of segmented images effective stimulation does not require placement of active contacts within the ANT proper. Fiber tracts are supposed to mediate therapeutic effects, similar to other well-established DBS targets in movement disorder surgery.
