Deep Brain Stimulation

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Nathalie Vayssiere, Simone Hemm, Michel Zanca, Marie Christine Picot, Alain Bonafe, Laura Cif, Philippe Frerebeau and Philippe Coubes

Object. The actual distortion present in a given series of magnetic resonance (MR) images is difficult to establish. The purpose of this study was to validate an MR imaging—based methodology for stereotactic targeting of the internal globus pallidus during electrode implantation in children in whom general anesthesia had been induced.

Methods. Twelve children (mean follow up 1 year) suffering from generalized dystonia were treated with deep brain stimulation by using a head frame and MR imaging. To analyze the influence of distortions at every step of the procedure, the geometrical characteristics of the frame were first controlled using the localizer as a phantom. Then pre- and postoperative coordinates of fixed anatomical landmarks and electrode positions, both determined with the head frame in place, were statistically compared.

No significant difference was observed between theoretical and measured dimensions of the localizer (Student's t-test, |t| > 2.2 for 12 patients) in the x, y, and z directions.

No significant differences were observed (Wilcoxon paired-sample test) between the following: 1) pre- and postoperative coordinates of the anterior commissure (AC) (Δx = 0.3 ± 0.29 mm and Δy = 0.34 ± 0.32 mm) and posterior commissure (PC) (Δx = 0.15 ± 0.18 mm and Δy = 0.34 ± 0.25 mm); 2) pre- and postoperative AC—PC distance (ΔL = 0.33 ± 0.22 mm); and 3) preoperative target and final electrode position coordinates (Δx = 0.24 ± 0.22 mm; Δy = 0.19 ± 0.16 mm).

Conclusions. In the authors' center, MR imaging distortions did not induce detectable errors during stereotactic surgery in dystonic children. Target localization and electrode implantation could be achieved using MR imaging alone after induction of general anesthesia. The remarkable postoperative improvement in these patients confirmed the accuracy of the procedure (Burke—Marsden—Fahn Dystonia Rating Scale score Δ = −83.8%).

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Cole A. Giller, Maureen Johns and Hanli Liu

✓ Localization of targets during stereotactic surgery is frequently accomplished by identification of the boundaries between the gray matter of various nuclei and the surrounding white matter. The authors describe an intracranial probe developed for this purpose, which uses near-infrared (NIR) light.

The probe fits through standard stereotactic holders and emits light at its tip. The scattered light is detected and analyzed by a spectrometer, with the slope of the trailing portion of the reflectance curve used as the measurement value.

Near-infrared readings were obtained during 27 neurosurgical procedures. The first three operations were temporal lobectomies, with values obtained from tracks in the resected specimen and resection bed. In the next five procedures, the probe was inserted stereotactically to a depth of 1 to 2 cm with measurements obtained every 1 mm. The probe was then used in 19 stereotactic procedures for movement disorders, obtaining measurements every 0.5 to 1 mm to target depths of 6 to 8 cm to interrogate subcortical structures. The NIR signals were correlated to distances beneath the cortical surface measured on postoperative computerized tomography or magnetic resonance imaging by using angle correction and three-dimensional reconstruction techniques.

The NIR values for white and gray matter obtained during the lobectomies were significantly different (white matter 2.5 ± 0.37, gray matter 0.82 ± 0.23 mean ± standard deviation). The NIR values from the superficial stereotactic tracks showed initial low values corresponding to cortical gray matter and high values corresponding to subcortical white matter.

There was good correlation between the NIR signals and postoperative imaging in the 19 stereotactic cases. Dips due to adjacent sulci, a plateau of high signal due to subcortical white matter, a dip in the NIR signal during passage through the ventricle, dips due to the caudate nucleus, and peaks due to the white matter capsule between ventricle and thalamus were constant features. The putamen—capsule boundary and the lamina externa and interna of the globus pallidus could be distinguished in three cases. Elevated signals corresponding to the thalamic floor were seen in 10 cases. Nuances such as prior lesions and nonspecific white matter changes were also detected. There was no incidence of morbidity associated with use of the probe. Data acquisition was straightforward and the equipment required for the studies was inexpensive.

The NIR probe described in this article seems to be able to detect gray—white matter boundaries around and within subcortical structures commonly encountered in stereotactic functional neurosurgery. This simple, inexpensive method deserves further study to establish its efficacy for stereotactic localization.

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Albert E. Telfeian, John A. Boockvar, Tanya Simuni, Jurg Jaggi, Brett Skolnick and Gordon H. Baltuch

✓ Deep brain stimulation (DBS) of the ventralis intermedius nucleus (Vim) is a safe and effective treatment for essential tremor. Bipolar disorder and essential tremor had each been reported to occur in association with Klinefelter syndrome but the three diseases have been reported to occur together in only one patient. The genetic basis and natural history of these disorders are not completely understood and may be related rather than coincidental. The authors report on a 23-year-old man with Klinefelter syndrome (47,XXY) and bipolar disorder who was treated successfully with unilateral DBS of the thalamic Vim for essential tremor.

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John A. Boockvar, Albert Telfeian, Gordon H. Baltuch, Brett Skolnick, Tanya Simuni, Matthew Stern, Marie L. Schmidt and John Q. Trojanowski

✓ Essential tremor can be suppressed with chronic, bilateral deep brain stimulation (DBS) of the ventralis intermedius nucleus (Vim), the cerebellar receiving area of the motor thalamus. The goal in this study was to correlate the location of the electrodes with the clinical efficacy of DBS in a patient with essential tremor. The authors report on a woman with essential tremor in whom chronic bilateral DBS directed to the ventral thalamus produced adequate tremor suppression until her death from unrelated causes 16 months after placement of the electrodes. Neuropathological postmortem studies of the brain in this patient demonstrated that both stimulators terminated in the Vim region of the thalamus, and that chronic DBS elicited minor reactive changes confined to the immediate vicinity of the electrode tracks. Although the authors could not identify neuropathological abnormalities specific to essential tremor, they believe that suppression of essential tremor by chronic DBS correlates with bilateral termination of the stimulators in the Vim region of the thalamus.

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Volker M. Tronnier and Wolfgang Fogel

✓ Pallidal stereotactic surgery is a well-accepted treatment alternative for Parkinson's disease. Another indication for this procedure is medically refractory dystonia, especially generalized dystonia with abnormal axial and extremity movements and postures. Improvement of dystonia after pallidotomy has been reported in several recent papers. In this report the authors describe three patients with generalized dystonia (two primary, one secondary) and their improvement after bilateral pallidal stimulation at follow-up times of between 6 and 18 months.

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Jamal M. Taha, Michele A. Janszen and Jacques Favre

Object. In published series of patients who undergo deep brain stimulation (DBS) of the thalamus the effects of unilateral stimulation on contralateral limb tremor have been reported. The authors detail their experience with bilateral thalamic DBS in the treatment of head, voice, and bilateral limb tremor and compare it with earlier studies of unilateral stimulation.

Methods. Twenty-three patients (six with Parkinson's disease, 15 with essential tremor, and two with multiple sclerosis) underwent 19 bilateral DBS procedures (nine staged, 10 simultaneous) and four procedures contralateral to thalamotomy to control tremor of the head in 10, voice in seven, and limbs in 20 patients. Limb tremor improvement was graded as follows: 4, no tremor; 3, stress-induced tremor; 2, functional improvement; 1, no functional improvement; and 0, persistent tremor. Improvement of head or voice tremor was graded as follows: 4, greater than 75%; 3, between 50% and 75%; 2, between 25% and 50%; 1, less than 25%; and 0, no improvement. The mean follow-up period was 10 months.

Twenty-two patients (96%) demonstrated improved tremor at the last follow-up review. Of 20 patients with bilateral limb tremor, 17 (85%) improved to Grades 3 and 4, two patients (10%) with multiple sclerosis improved to Grade 2, and one (5%) exhibited tremor recurrence 8 months later. Nine (90%) of 10 patients with severe head tremor improved to Grades 4 or 3. Six (86%) of seven patients with voice tremor improved to Grade 3. Seven patients (30%) developed dysarthria, and seven (30%) developed disequilibrium; symptoms reversed in the majority of patients after the stimulation parameters were changed. One patient (4%) developed mild memory decline. There were no deaths.

Conclusions. The following findings are reported: 1) bilateral thalamic DBS and stimulation contralateral to thalamotomy are safe; 2) staging the procedure does not reduce the risk of dysarthria or gait disequilibrium; and 3) head and voice tremor are primary indications for bilateral DBS.

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Ali R. Rezai, Andres M. Lozano, Adrian P. Crawley, Michael L. G. Joy, Karen D. Davis, Chun L. Kwan, Jonathan O. Dostrovsky, Ronald R. Tasker and David J. Mikulis

✓ The utility of functional magnetic resonance (fMR) imaging in patients with implanted thalamic electrodes has not yet been determined. The aim of this study was to establish the safety of performing fMR imaging in patients with thalamic deep brain stimulators and to determine the value of fMR imaging in detecting cortical and subcortical activity during stimulation.

Functional MR imaging was performed in three patients suffering from chronic pain and two patients with essential tremor. Two of the three patients with pain had undergone electrode implantation in the thalamic sensory ventralis caudalis (Vc) nucleus and the other had undergone electrode implantation in both the Vc and the periventricular gray (PVG) matter. Patients with tremor underwent electrode implantation in the ventralis intermedius (Vim) nucleus. Functional MR imaging was performed during stimulation by using a pulse generator connected to a transcutaneous extension lead. Clinically, Vc stimulation evoked paresthesias in the contralateral body, PVG stimulation evoked a sensation of diffuse internal body warmth, and Vim stimulation caused tremor arrest.

Functional images were acquired using a 1.5-tesla MR imaging system. The Vc stimulation at intensities provoking paresthesias resulted in activation of the primary somatosensory cortex (SI). Stimulation at subthreshold intensities failed to activate the SI. Additional stimulation-coupled activation was observed in the thalamus, the secondary somatosensory cortex (SII), and the insula. In contrast, stimulation of the PVG electrode did not evoke paresthesias or activate the SI, but resulted in medial thalamic and cingulate cortex activation. Stimulation in the Vim resulted in thalamic, basal ganglia, and SI activation.

An evaluation of the safety of the procedure indicated that significant current could be induced within the electrode if a faulty connecting cable (defective insulation) came in contact with the patient. Simple precautions, such as inspection of wires for fraying and prevention of their contact with the patient, enabled the procedure to be conducted safely. Clinical safety was further corroborated by performing 86 MR studies in patients in whom electrodes had been implanted with no adverse clinical effects.

This is the first report of the use of fMR imaging during stimulation with implanted thalamic electrodes. The authors' findings demonstrate that fMR imaging can safely detect the activation of cortical and subcortical neuronal pathways during stimulation and that stimulation does not interfere with imaging. This approach offers great potential for understanding the mechanisms of action of deep brain stimulation and those underlying pain and tremor generation.

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Charles D. Ray

✓ A new burr-hole ring and cap are described. The threaded ring is C-shaped, holding itself in the burr hole by elastic recoil. A ventricular catheter or deep brain electrode may be passed through the slotted ring and anchored in place by means of a mushroom-shaped silicone rubber cap. The cap fills, sealing the plug. This simple two-part device, originally designed for use with a deep brain stimulator system, may also be used as a standard ⅝-in. (16 mm) burr-hole plug.