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Richard G. Bittar, André Olivier, Abbas F. Sadikot, Frederick Andermann, G. Bruce Pike and David C. Reutens

Object. Accurate identification of eloquent cortex is important to ensure that resective surgery in the region surrounding the central sulcus is performed with minimum risk of permanent neurological deficit. Functional localization has traditionally been accomplished using intraoperative cortical stimulation (ICS). However, this technique suffers from several disadvantages that make the development and validation of noninvasive methods desirable. Functional localization accomplished by activation studies in which positron emission tomography (PET) scanning and the tracer [15O]H2O have been used has been shown to correlate well with the results of ICS. Another noninvasive method for functional localization is functional magnetic resonance (fMR) imaging. We compared the locations of activation peaks obtained in individual patients using fMR and [15O]H2O PET imaging.

Methods. Twenty-six combined PET activation—fMR imaging studies were performed in 11 patients who were admitted for evaluation before undergoing surgery in the region surrounding the central sulcus. The PET scans were obtained using bolus injections of the cerebral blood flow tracer [15O]H2O (10 mCi). Multislice T2*-weighted gradient-echo echoplanar images were acquired using a 1.5-tesla MR imaging system. Activation maps were aligned with anatomical MR images and transformed into stereotactic space, after which the locations of activation peaks obtained using both modalities were compared. The average distance between activation peaks obtained using fMR imaging and those obtained using PET imaging was 7.9 ± 4.8 mm (p > 0.05), with 96% of the peaks being located on either the same or adjacent sulci and gyri. Overlapping of voxels activated by each modality occurred in 92% of the studies. Functional MR imaging failed to activate the primary sensorimotor cortex in one study and produced results that were ambiguous in the clinical setting in three cases.

Conclusions. Overall, fMR imaging produced activation that correlated well with that obtained using PET scanning. Discrepancies between the sites of activation identified using these two techniques may reflect differences in their physiological bases.

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Emma G. Duerden, Kirk W. Finnis, Terry M. Peters and Abbas F. Sadikot

Object

The somatotopic organization of the motor fibers within the posterior limb of the internal capsule (IC) in humans remains unclear. Several electrophysiological atlases created from stimulation during stereotactic neurosurgery have suggested that there is considerable overlap between representations of body parts. Overlap reported in these studies may have been due to linear scaling methods applied to the data that were unable to account for individual anatomical variability. In the current work, the authors attempted to overcome these limitations by using a nonlinear registration technique to better understand the spatial location and extent of the body-part representations in the IC.

Methods

Data were acquired during 30 cases of deep brain neurosurgery in which the IC was electrically stimulated to localize the ventrolateral nucleus for a subsequent thalamotomy or implantation of a thalamic deep brain stimulator. Motor responses from the tongue, face, arm, or leg were evoked in the IC and coded in the patient's native MR imaging space. The tagged MR images were then nonlinearly registered to a high-resolution template MR image. This work resulted in a functional electrophysiological atlas demonstrating the locations of body-part representations in the posterior limb of the IC that takes individual anatomical variability into account. To further understand the spatial location and extent of the motor responses, the electrophysiological data points were transformed into 3D probability maps that describe the likelihood of obtaining motor responses in the posterior limb of the IC.

Results

The analyses suggest a reliable face-anterior, arm-intermediate, and leg-posterior somatotopic organization in the posterior limb of the IC with little overlap between the body-part representations.

Conclusions

This probabilistic atlas of functional responses evoked by stimulating the posterior limb of the IC provides better understanding of the anatomical organization of descending motor fibers, can be used for indirect intraoperative confirmation of the location of the ventrolateral thalamus, and is applicable to clinical and research MR imaging studies requiring information on spatial organization of motor fibers at the thalamic level in the human brain.

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Silvain Bériault, Abbas F. Sadikot, Fahd Alsubaie, Simon Drouin, D. Louis Collins and G. Bruce Pike

Careful trajectory planning on preoperative vascular imaging is an essential step in deep brain stimulation (DBS) to minimize risks of hemorrhagic complications and postoperative neurological deficits. This paper compares 2 MRI methods for visualizing cerebral vasculature and planning DBS probe trajectories: a single data set T1-weighted scan with double-dose gadolinium contrast (T1w-Gd) and a multi–data set protocol consisting of a T1-weighted structural, susceptibility-weighted venography, and time-of-flight angiography (T1w-SWI-TOF). Two neurosurgeons who specialize in neuromodulation surgery planned bilateral STN DBS in 18 patients with Parkinson's disease (36 hemispheres) using each protocol separately. Planned trajectories were then evaluated across all vascular data sets (T1w-Gd, SWI, and TOF) to detect possible intersection with blood vessels along the entire path via an objective vesselness measure. The authors' results show that trajectories planned on T1w-SWI-TOF successfully avoided the cerebral vasculature imaged by conventional T1w-Gd and did not suffer from missing vascular information or imprecise data set registration. Furthermore, with appropriate planning and visualization software, trajectory corridors planned on T1w-SWI-TOF intersected significantly less fine vasculature that was not detected on the T1w-Gd (p < 0.01 within 2 mm and p < 0.001 within 4 mm of the track centerline). The proposed T1w-SWI-TOF protocol comes with minimal effects on the imaging and surgical workflow, improves vessel avoidance, and provides a safe cost-effective alternative to injection of gadolinium contrast.

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Richard G. Bittar, André Olivier, Abbas F. Sadikot, Frederick Andermann and David C. Reutens

Object. Changes in cortical representation in patients with cerebral lesions may alter the correlation between cortical anatomy and function. This is of potential clinical significance when the extent of cortical resection is based on surface anatomical landmarks.

Methods. Fifty-one patients with supratentorial lesions were studied. Nineteen harbored noncentral lesions (no involvement of pre- or postcentral gyrus), whereas 32 had central lesions. Control studies consisted of stimulation of the hand contralateral to the unaffected hemisphere. Positron emission tomography activation studies were performed using the [15O]H2O tracer. Somatosensory stimulation of the hand or foot was performed using a mechanical vibrator. Motor activation consisted of hand clenching or foot tapping. The t-statistic volumes were generated from images showing the mean change in regional cerebral blood flow, and coregistered with a T1-weighted magnetic resonance image. At the threshold selected, exclusive contralateral primary sensorimotor cortex activation was elicited in 100% of the control studies. A different pattern of cortical activation was associated with central lesions in 35 (78%) of 45 patients, which occurred significantly more often than with noncentral lesions (eight [31%] of 26 patients). The most common difference in the pattern of activation with central lesions was activation of cortical regions outside the central area (including the supplementary sensorimotor area and the secondary somatosensory cortex). No sensorimotor activation was observed in gyri adjacent to the pre- or postcentral gyrus.

Conclusions. Central lesions are more frequently associated with altered patterns in activation than lesions in noncentral locations. Characteristic patterns include activation of secondary sensorimotor areas. The absence of activation in gyri adjacent to the sensorimotor strip has clinical significance for the planning of resections in the central area.

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Jeffrey D. Atkinson, D. Louis Collins, Gilles Bertrand, Terry M. Peters, G. Bruce Pike and Abbas F. Sadikot

Object. Renewed interest in stereotactic neurosurgery for movement disorders has led to numerous reports of clinical outcomes associated with different treatment strategies. Nevertheless, there is a paucity of autopsy and imaging data that can be used to describe the optimal size and location of lesions or the location of implantable stimulators. In this study the authors correlated the clinical efficacy of stereotactic thalamotomy for tremor with precise anatomical localization by using postoperative magnetic resonance (MR) imaging and an integrated deformable digital atlas of subcortical structures.

Methods. Thirty-one lesions were created by stereotactic thalamotomy in 25 patients with tremor-dominant Parkinson disease. Lesion volume and configuration were evaluated by reviewing early postoperative MR images and were correlated with excellent, good, or fair tremor outcome categories. To allow valid comparisons of configurations of lesions with respect to cytoarchitectonic thalamic boundaries, the MR image obtained in each patient was nonlinearly deformed into a standardized MR imaging space, which included an integrated atlas of the basal ganglia and thalamus. The volume and precise location of lesions associated with different clinical outcomes were compared using nonparametric statistical methods. Probabilistic maps of lesions in each tremor outcome category were generated and compared.

Statistically significant differences in lesion location between excellent and good, and excellent and fair outcome categories were demonstrated. On average, lesions associated with excellent outcomes involved thalamic areas located more posteriorly than sites affected by lesions in the other two outcome groups. Subtraction analysis revealed that lesions correlated with excellent outcomes necessarily involved the interface of the nucleus ventralis intermedius (Vim; also known as the ventral lateral posterior nucleus [VLp]) and the nucleus ventrocaudalis (Vc; also known as the ventral posterior [VP] nucleus). Differences in lesion volume among outcome groups did not achieve statistical significance.

Conclusions. Anatomical evaluation of lesions within a standardized MR image—atlas integrated reference space is a useful method for determining optimal lesion localization. The results of an analysis of probabilistic maps indicates that optimal relief of tremor is associated with lesions involving the Vim (VLp) and the anterior Vc (VP).

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Richard G. Bittar, André Olivier, Abbas F. Sadikot, Frederick Andermann, Roch M. Comeau, Martin Cyr, Terrence M. Peters and David C. Reutens

Object. To investigate the utility of [15O]H2O positron emission tomography (PET) activation studies in the presurgical mapping of primary somatosensory cortex, the authors compared the magnitude and location of activation foci obtained using PET scanning with the results of intraoperative cortical stimulation (ICS).

Methods. The authors used PET scanning and vibrotactile stimulation (of the face, hand, or foot) to localize the primary somatosensory cortex before surgical resection of mass lesions or epileptogenic foci affecting the central area in 20 patients. With the aid of image-guided surgical systems, the locations of significant activation foci on PET scanning were compared with those of positive ICS performed at craniotomy after the patient had received a local anesthetic agent. In addition, the relationship between the magnitude and statistical significance of blood flow changes and the presence of positive ICS was examined.

In 22 (95.6%) of 23 statistically significant (p < 0.05) PET activation foci, spatially concordant sites on ICS were also observed. Intraoperative cortical stimulation was positive in 40% of the PET activation studies that did not result in statistically significant activation. In the patients showing these results, there was a clearly identifiable t-statistic peak that was spatially concordant with the site of positive ICS in the sensorimotor area. All PET activation foci with a t statistic greater than 4.75 were associated with spatially concordant sites of positive ICS. All PET activation foci with a t statistic less than 3.2 were associated with negative ICS.

Conclusions. Positron emission tomography is an accurate method for mapping the primary somatosensory cortex before surgery. The need for ICS, which requires local anesthesia, may be eliminated when PET foci with high (> 4.75) or low (< 3.20) t-statistic peaks are elicited by vibrotactile stimulation.

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Richard G. Bittar, André Olivier, Abbas F. Sadikot, Frederick Andermann, Roch M. Comeau, Martin Cyr, Terrence M. Peters and David C. Reutens

Object

To investigate the utility of [15O]H2O positron emission tomography (PET) activation studies in the presurgical mapping of primary somatosensory cortex, the authors compared the magnitude and location of activation foci obtained using PET scanning with the results of intraoperative cortical stimulation (ICS).

Methods

The authors used PET scanning and vibrotactile stimulation (of the face, hand, or foot) to localize the primary somatosensory cortex before surgical resection of mass lesions or epileptogenic foci affecting the central area in 20 patients. With the aid of image-guided surgical systems, the locations of significant activation foci on PET scanning were compared with those of positive ICS performed at craniotomy after the patient had received a local anesthetic agent. In addition, the relationship between the magnitude and statistical significance of blood flow changes and the presence of positive ICS was examined.

In 22 (95.6%) of 23 statistically significant (p < 0.05) PET activation foci, spatially concordant sites on ICS were also observed. Intraoperative cortical stimulation was positive in 40% of the PET activation studies that did not result in statistically significant activation. In the patients showing these results, there was a clearly identifiable t-statistic peak that was spatially concordant with the site of positive ICS in the sensorimotor area. All PET activation foci with a t statistic greater than 4.75 were associated with spatially concordant sites of positive ICS. All PET activation foci with a t statistic less than 3.2 were associated with negative ICS.

Conclusions

Positron emission tomography is an accurate method for mapping the primary somatosensory cortex before surgery. The need for ICS, which requires local anesthesia, may be eliminated when PET foci with high (> 4.75) or low (< 3.20) t-statistic peaks are elicited by vibrotactile stimulation.

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Andres M. Lozano, Peter Giacobbe, Clement Hamani, Sakina J. Rizvi, Sidney H. Kennedy, Theodore T. Kolivakis, Guy Debonnel, Abbas F. Sadikot, Raymond W. Lam, Andrew K. Howard, Magda Ilcewicz-Klimek, Christopher R. Honey and Helen S. Mayberg

Object

Deep brain stimulation (DBS) has been recently investigated as a treatment for major depression. One of the proposed targets for this application is the subcallosal cingulate gyrus (SCG). To date, promising results after SCG DBS have been reported by a single center. In the present study the authors investigated whether these findings may be replicated at different institutions. They conducted a 3-center prospective open-label trial of SCG DBS for 12 months in patients with treatment-resistant depression.

Methods

Twenty-one patients underwent implantation of bilateral SCG electrodes. The authors examined the reduction in Hamilton Rating Scale for Depression (HRSD-17) score from baseline (RESP50).

Results

Patients treated with SCG DBS had an RESP50 of 57% at 1 month, 48% at 6 months, and 29% at 12 months. The response rate after 12 months of DBS, however, increased to 62% when defined as a reduction in the baseline HRSD-17 of 40% or more. Reductions in depressive symptomatology were associated with amelioration in disease severity in patients who responded to surgery.

Conclusions

Overall, findings from this study corroborate the results of previous reports showing that outcome of SCG DBS may be replicated across centers.