A connectomic approach for subcallosal cingulate deep brain stimulation surgery: prospective targeting in treatment-resistant depression.

Target identification and contact selection are known contributors to variability in efficacy across different clinical indications of deep brain stimulation surgery. A retrospective analysis of responders to subcallosal cingulate deep brain stimulation (SCC DBS) for depression demonstrated the common impact of the electrical stimulation on a stereotypic connectome of converging white matter bundles (forceps minor, uncinate fasciculus, cingulum and fronto-striatal fibers). To test the utility of a prospective connectomic approach for SCC DBS surgery, this pilot study used the four-bundle tractography 'connectome blueprint' to plan surgical targeting in 11 participants with treatment-resistant depression. Before surgery, targets were selected individually using deterministic tractography. Selection of contacts for chronic stimulation was made by matching the post-operative probabilistic tractography map to the pre-surgical deterministic tractography map for each subject. Intraoperative behavioral responses were used as a secondary verification of location. A probabilistic tract map of all participants demonstrated inclusion of the four bundles as intended, matching the connectome blueprint previously defined. Eight of 11 patients (72.7%) were responders and 5 were remitters after 6 months of open-label stimulation. At one year, 9 of 11 patients (81.8%) were responders, with 6 of them in remission. These results support the utility of a group probabilistic tractography map as a connectome blueprint for individualized, patient-specific, deterministic tractography targeting, confirming retrospective findings previously published. This new method represents a connectomic approach to guide future SCC DBS studies.

A meta-analysis of repetitive transcranial magnetic stimulation in the treatment of depression.

Repetitive transcranial magnetic stimulation (rTMS) is an emerging potential treatment for depression, but the data supporting its efficacy have not been systematically reviewed. The purpose of this study was to conduct a meta-analysis of rTMS trials in the treatment of depression. A search for all published and unpublished sham-controlled studies of left or right prefrontal cortical rTMS in the treatment of depression evaluated by the Hamilton Depression Rating Scale (HDRS) was conducted using no language restrictions. Fixed- and random-effects meta-analyses were performed on 12 studies comparing the decrease in HDRS scores achieved with rTMS and sham stimulation. Initial results with a fixed-effects analysis failed homogeneity testing; thus, a random-effects analysis was used to calculate all results. In 12 studies (16 individual effect sizes), the weighted mean effect size was 0.81 (95% CI: 0.42-1.20, P < .001). For studies using left dorsolateral pre-frontal cortex (DLPFC) stimulation (11 studies, 14 effect sizes), the weighted mean effect size was 0.89 (95% CI: 0.44-1.35, P < .001). For studies using left DLPFC stimulation in a parallel-groups design (seven studies, nine effect sizes), the weighted mean effect size was 0.88 (95% CI: 0.22-1.54, P < .01). No study showed a mean decrease in HDRS scores of > 50%, and the number of responders to rTMS (defined as a > 50% decrease in HDRS scores) across studies was relatively small (13.7% with rTMS versus 7.9% with sham stimulation). rTMS is statistically superior to sham stimulation in the treatment of depression, showing a moderate to large effect size. However, the clinical significance of these results is modest. The differences in response to rTMS across studies are not clearly explained, and, therefore, more research is needed.

Magnetic resonance imaging versus computed tomography for target localization in functional stereotactic neurosurgery.

OBJECTIVE: To determine whether magnetic resonance imaging (MRI), compared with computed tomography (CT), provides consistent and accurate target localization for ventrolateral thalamotomy and posteroventral pallidotomy. METHODS: For 93 procedures (78 pallidotomies and 15 thalamotomies) in 83 patients, coordinates for the anterior commissure, posterior commissure, and stereotactic target were calculated from MRI- and CT-derived images and compared. RESULTS: The mean differences for the target were -0.41 mm on the x axis (P < 0.001), 0.06 mm on the y axis (P = 0.412), and -0.34 mm on the z axis (P < 0.01). The mean absolute differences were 0.53 mm on the x axis (median, 0.50 mm; range, 0.00-2.00 mm), 0.46 mm on the y axis (median, 0.50 mm; range, 0.00-2.00 mm), and 0.78 mm on the z axis (median, 0.50 mm; range, 0.00-6.00 mm). The mean three-dimensional distance between MRI- and CT-derived coordinates for the anterior commissure was 1.65 mm, with a distance of more than 4 mm in two cases (2%). The mean three-dimensional distance for the posterior commissure was 1.65 mm, with a distance of more than 4 mm in two cases (2%). The mean three-dimensional distance for the target was 1.25 mm (median, 1.14 mm; range, 0.00-6.27 mm), with a distance of more than 4 mm in one case (1%). CONCLUSION: Statistically significant but relatively small differences between MRI- and CT-derived target coordinates were found. In some cases (approximately 2% of this series), the differences between MRI- and CT-derived coordinates may be relatively large (greater than 4 mm and up to 8 mm). However, given the superior anatomic resolution of MRI and the nature of the stereotactic procedures under consideration, we conclude that MRI, when validated within an institution, may be used alone for target localization in pallidotomy and thalamotomy.

Utilization of impedance measurements in pallidotomy using a monopolar electrode.

OBJECT: This study was performed to evaluate the reliability and utility of using monopolar impedance monitoring for estimation of the location of the thermocouple electrode during a pallidotomy procedure. METHODS: In 26 patients, impedance profiles were measured at 2-mm intervals and anatomical boundaries were marked on postoperative MRI studies in 19 patients. The pattern of change in impedance as the electrode was towards the target coordinates in the globus pallidus was studied empirically in relation to MRI-defined anatomy and by electrical stimulations. The pattern of impedance change was of greater reliability than absolute impedance values. A drop in impedance was noted in 10 cases where the electrode entered the putamen or globus pallidus upon exiting the internal capsule, and in 9 of these this drop was measured before or at the distal boundary of the internal capsule. A variable pattern in the region of the base of the globus pallidus was observed, with 10 of 19 cases demonstrating a decrease and 8 cases an increase, consistent with the proximity of a CSF cistern in the former and the ansa lenticularis and optic tract in the latter. Simulations showed that the monopolar electrode was more sensitive to the approach of a boundary than the bipolar electrode. CONCLUSION: Our measurements and simulations suggest that a monopolar electrode could predict a nearby region of high or low impedance before penetrating it and a trend of decreasing impedance as the distal edge of the globus pallidus is approached.