title: Defining the anterior nucleus of the thalamus (ANT) as a deep brain stimulation target in refractory epilepsy: Delineation using 3 T MRI and intraoperative microelectrode recording.
abstract: BACKGROUND
  Deep brain stimulation (DBS) is a minimally invasive and reversible method to treat an increasing number of neurological and psychiatric disorders, including epilepsy. Targeting poorly defined deep structures is based in large degree on stereotactic atlas information, which may be a major source of inconsistent treatment effects.
  
  
  OBJECTIVE
  In the present study, we aimed to study whether a recently approved target for epilepsy (anterior nucleus of thalamus, ANT) is visualized in clinically established 3 T MRI and whether ANT is delineated using intraoperative microelectrode recording (MER). We have especially focused on individual variation in the location of ANT in stereotactic space. We also aimed to demonstrate the role of individual variation in interpretation of MER data by projecting samples onto AC-PC (anterior and posterior commissure) and ANT-normalized coordinate systems.
  
  
  METHODS
  Detailed analysis of ANT delineations in 3 T MRI short tau inversion recovery (STIR) images from eight patients undergoing DBS for refractory epilepsy was performed. Coronal and sagittal cross-sectional models of ANT were plotted in the AC-PC coordinate system to study individual variation. A total of 186 MER samples collected from 10 DBS trajectories and 5 patients were analyzed, and the location of each sample was calculated and corrected accordingly to the location of the final DBS electrode and projected to the AC-PC or coordinate system normalized to ANT.
  
  
  RESULTS
  Most of the key structures in the anatomic atlas around ANT (mammillothalamic tract and external medullary lamina) were identified in STIR images allowing visual delineation of ANT. We observed a high degree of anatomical variation in the location of ANT, and the cross-sectional areas overlapped by study patients decreased in a linear fashion with an increasing number of patients. MER information from 10 individual trajectories correlated with STIR signal characteristics by demonstrating a spike-negative zone, presumably white matter layer, at the lateral aspect of ANT in ANT-normalized coordinate system as predicted by STIR images. However, MER information projected to the AC-PC coordinate system was not able to delineate ANT.
  
  
  CONCLUSIONS
  ANT is delineated in 3 T MRI by visualization of a thin white matter lamina between ANT and other nuclear groups that lack spiking activity. Direct targeting in the anterior thalamic area is superior to indirect targeting due to extensive individual variation in the location of ANT. Without detailed imaging information, however, a single trajectory MER has little localizing value.
authors.affiliation: Department of Neurosciences and Rehabilitation, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Möttönen
authors.affiliation: Department of Neurosurgery, Oulu University Hospital, P.O. Box 21, Oulu 90029, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Katisko
authors.affiliation: Department of Neurosciences and Rehabilitation, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Haapasalo
authors.affiliation: Department of Neurosciences and Rehabilitation, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Tähtinen
authors.affiliation: Medical Imaging Centre, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Kiekara
authors.affiliation: Medical Imaging Centre, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: V
authors.initials: V
authors.lastname: Kähärä
authors.affiliation: Department of Neurosciences and Rehabilitation, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Peltola
authors.affiliation: Department of Neurosciences and Rehabilitation, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Öhman
authors.affiliation: Department of Neurosciences and Rehabilitation, Tampere University Hospital, P.O. Box 2000, Tampere 33521, Finland.
authors.forename: K
authors.initials: K
authors.lastname: Lehtimäki
mesh_terms: D020643:Anterior Thalamic Nuclei / Q000033:anatomy & histology*; D015331:Cohort Studies; D046690:Deep Brain Stimulation; D000069279:Drug Resistant Epilepsy / Q000628:therapy*; D004567:Electrodes, Implanted; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods*; D008279:Magnetic Resonance Imaging; D008839:Microelectrodes
keywords: 3D-T1W, 3-dimensional (multi-planar reconstruction) T1-weighted image; AC, anterior commissure; ANT, anterior nucleus of thalamus; Anterior nucleus; DBS, deep brain stimulation; Deep brain stimulation; Epilepsy; MCP, mid-commissural point; MER, microelectrode recording; Magnetic resonance imaging; PC, posterior commissure; STIR, short tau inversion recovery; T2W, T2-weighted image; Thalamus; VA, ventral anterior nucleus of thalamus