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Aviva Abosch, Neda Bernasconi, Warren Boling, Marilyn Jones-Gotman, Nicole Poulin, François Dubeau, Frederick Andermann and André Olivier

Object. Selective amygdalohippocampectomy (SelAH) is used in the treatment of mesial temporal lobe epilepsy (MTLE). The goal of this study was to determine factors predictive of poor postoperative seizure control (Engel Class III or IV) following SelAH.

Methods. A retrospective study was conducted of 27 patients with poor seizure control postoperatively (Engel III/IV group), in comparison with 27 patients who were free from seizures after surgery (Engel I/II group). The results of electroencephalography, magnetic resonance (MR) imaging, and pathological studies were reviewed, and volumetric MR image analysis was used to compare the extent of the mesial structures that had been resected.

In 56% of patients in the Engel III/IV group, significant bitemporal abnormalities were displayed on preoperative EEG studies, compared with 24% of patients in the Engel I/II group (p < 0.05). An analysis of preoperative MR images disclosed five patients (19%) in the Engel III/IV group and no patient in the Engel I/II group with normal hippocampal volumes bilaterally. Thirteen patients in the Engel III/IV group subsequently underwent either extension of the SelAH (six cases) or a corticoamygdalohippocampectomy (seven patients). Three patients from the former and one patient from the latter subgroup subsequently became seizure free (four patients total [34%]). The remaining nine patients did not improve, despite the fact that they had undergone near-total resection of mesial structures.

Conclusions. The majority of patients receiving suboptimal seizure control following SelAH did not meet the criteria for unilateral MTLE, based on EEG, MR imaging, and/or histopathological studies. These patients were therefore unlikely to benefit from additional resection of mesial structures. With the benefits of modern imaging, and by strict adherence to selection criteria, SelAH can be predicted to yield excellent postoperative seizure control for nearly all patients with unilateral MTLE. There remains a subpopulation, however, that meets the criteria for MTLE, but does not become free from seizure following SelAH.

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Jean A. Saint-Cyr, Tasnuva Hoque, Luiz C. M. Pereira, Jonathan O. Dostrovsky, William D. Hutchison, David J. Mikulis, Aviva Abosch, Elspeth Sime, Anthony E. Lang and Andres M. Lozano

Object. The authors sought to determine the location of deep brain stimulation (DBS) electrodes that were most effective in treating Parkinson disease (PD).

Methods. Fifty-four DBS electrodes were localized in and adjacent to the subthalamic nucleus (STN) postoperatively by using magnetic resonance (MR) imaging in a series of 29 patients in whom electrodes were implanted for the treatment of medically refractory PD, and for whom quantitative clinical assessments were available both pre- and postoperatively. A novel MR imaging sequence was developed that optimized visualization of the STN. The coordinates of the tips of these electrodes were calculated three dimensionally and the results were normalized and corrected for individual differences by using intraoperative neurophysiological data (mean 5.13 mm caudal to the midcommissural point [MCP], 8.46 mm inferior to the anterior commissure—posterior commissure [AC—PC], and 10.2 mm lateral to the midline).

Despite reported concerns about distortion on the MR image, reconstructions provided consistent data for the localization of electrodes. The neurosurgical procedures used, which were guided by combined neuroimaging and neurophysiological methods, resulted in the consistent placement of DBS electrodes in the subthalamus and mesencephalon such that the electrode contacts passed through the STN and dorsally adjacent fields of Forel (FF) and zona incerta (ZI). The mean location of the clinically effective contacts was in the anterodorsal STN (mean 1.62 mm posterior to the MCP, 2.47 mm inferior to the AC—PC, and 11.72 mm lateral to the midline). Clinically effective stimulation was most commonly directed at the anterodorsal STN, with the current spreading into the dorsally adjacent FF and ZI.

Conclusions. The anatomical localization of clinically effective electrode contacts provided in this study yields useful information for the postoperative programming of DBS electrodes.

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Aviva Abosch, William D. Hutchison, Jean A. Saint-Cyr, Jonathan O. Dostrovsky and Andres M. Lozano

Object. The subthalamic nucleus (STN) is a target in the surgical treatment of Parkinson disease (PD). Little is known about the neurons within the human STN that modulate movement. The authors' goal was to examine the distribution of movement-related neurons within the STN of humans by using microelectrode recording to identify neuronal receptive fields.

Methods. Data were retrospectively collected from microelectrode recordings that had been obtained in 38 patients with PD during surgery for placement of STN deep brain stimulation electrodes. The recordings had been obtained in awake, nonsedated patients. Antiparkinsonian medications were withheld the night before surgery. Neuronal discharges were amplified, filtered, and displayed on an oscilloscope and fed to an audio monitor. The receptive fields were identified by the presence of reproducible, audible changes in the firing rate that were time-locked to the movement of specific joint(s).

The median number of electrode tracks per patient was six (range two–nine). The receptive fields were identified in 278 (55%) of 510 STN neurons studied. One hundred one tracks yielded receptive field data. Fourteen percent of 64 cells tested positive for face receptive fields, 32% of 687 cells tested positive for upper-extremity receptive fields, and 21% of 242 cells tested positive for lower-extremity receptive fields. Sixty-eight cells (24%) demonstrated multiple-joint receptive fields. Ninety-three cells (65%) with movement-related receptive fields were located in the dorsal half of the STN, and 96.8% of these were located in the rostral two thirds of the STN. Analysis of receptive field locations from pooled data and along individual electrode tracks failed to reveal a consistent somatotopic organization.

Conclusions. Data from this study demonstrate a regional compartmentalization of neurons with movement-related receptive fields within the STN, supporting the existence of specific motor territories within the STN in patients suffering from PD.