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John Spooner, Hong Yu, Chris Kao, Karl Sillay and Peter Konrad

✓The authors present a case in which high-frequency electrical stimulation of the cingulum using standard deep brain stimulation (DBS) technology resulted in pain relief similar to that achieved with cingulotomy and superior to that achieved with periventricular gray matter (PVG) stimulation.

This patient had a complete spinal cord injury at the C-4 level and suffered from medically refractory neuropathic pain. He underwent placement of bilateral cingulum and unilateral PVG DBS electrodes and a 1-week blinded stimulation trial prior to permanent implantation of a pulse generator. During the stimulation trial, the patient's pain level was assessed using a visual analog scale, and pain medication usage was recorded. During this period the patient was blinded to stimulation parameters. Stimulation of the cingulum provided better pain control than PVG stimulation or medication alone.

The authors believe that cingulum stimulation can benefit patients with severe neuropathic pain that is refractory to other treatments. Advantages over cingulotomy include reversibility and the ability to adjust stimulation parameters for optimum efficacy.

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Hong Yu, Tom L. Yao, John Spooner, Jennifer R. Stumph, Ray Hester and Peter E. Konrad

✓Choroid plexus papilloma is a benign central nervous system tumor that occasionally spreads along the subarachnoid space. The authors report the case of a 49-year-old man who presented with back pain 19 years after resection of a posterior fossa choroid plexus papilloma. Magnetic resonance imaging revealed multiple spinal lesions without any residual or recurrent intracranial tumor. All spinal lesions were resected and histologically diagnosed as atypical choroid plexus papilloma. The authors suggest that patients in whom choroid plexus papilloma is diagnosed should undergo total neuraxis imaging at the time of initial diagnosis as well as periodic follow-up examinations after resection to rule out drop metastases.

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Amirali Toossi, Dirk G. Everaert, Peter Seres, Jacob L. Jaremko, Kevin Robinson, C. Chris Kao, Peter E. Konrad and Vivian K. Mushahwar

OBJECTIVE

The overall goal of this study was to develop an image-guided spinal stereotactic setup for intraoperative intraspinal microstimulation (ISMS). System requirements were as follows: 1) ability to place implants in various segments of the spinal cord, targeting the gray matter with a < 0.5-mm error; 2) modularity; and 3) compatibility with standard surgical tools.

METHODS

A spine-mounted stereotactic system was developed, optimized, and tested in pigs. The system consists of a platform supporting a micromanipulator with 6 degrees of freedom. It is modular and flexible in design and can be applied to various regions of the spine. An intraoperative ultrasound imaging technique was also developed and assessed for guidance of electrode alignment prior to and after electrode insertion into the spinal cord. Performance of the ultrasound-guided stereotactic system was assessed both in pigs (1 live and 6 fresh cadaveric pigs) and on the bench using four gelatin-based surrogate spinal cords. Pig experiments were conducted to evaluate the performance of ultrasound imaging in aligning the electrode trajectory using three techniques and under two conditions. Benchtop experiments were performed to assess the performance of ultrasound-guided targeting more directly. These experiments were used to quantify the accuracy of electrode alignment as well as assess the accuracy of the implantation depth and the error in spatial targeting within the gray matter of the spinal cord. As proof of concept, an intraoperative ISMS experiment was also conducted in an additional live pig using the stereotactic system, and the resulting movements and electromyographic responses were recorded.

RESULTS

The stereotactic system was quick to set up (< 10 minutes) and provided sufficient stability and range of motion to reach the ISMS targets reliably in the pigs. Transverse ultrasound images with the probe angled at 25°–45° provided acceptable contrast between the gray and white matter of the spinal cord. In pigs, the largest electrode alignment error using ultrasound guidance, relative to the minor axis of the spinal cord, was ≤ 3.57° (upper bound of the 95% confidence interval). The targeting error with ultrasound guidance in bench testing for targets 4 mm deep into the surrogate spinal cords was 0.2 ± 0.02 mm (mean ± standard deviation).

CONCLUSIONS

The authors developed and evaluated an ultrasound-guided spinal stereotactic system for precise insertion of intraspinal implants. The system is compatible with existing spinal instrumentation. Intraoperative ultrasound imaging of the spinal cord aids in alignment of the implants before insertion and provides feedback during and after implantation. The ability of ultrasound imaging to distinguish between spinal cord gray and white matter also improves confidence in the localization of targets within the gray matter. This system would be suitable for accurate guidance of intraspinal electrodes and drug or cell injections.

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Michael C. Dewan, Robert Shults, Andrew T. Hale, Vishad Sukul, Dario J. Englot, Peter Konrad, Hong Yu, Joseph S. Neimat, William Rodriguez, Benoit M. Dawant, Srivatsan Pallavaram and Robert P. Naftel

OBJECTIVE

Stereotactic electroencephalography (SEEG) is being used with increasing frequency to interrogate subcortical, cortical, and multifocal epileptic foci. The authors describe a novel technique for SEEG in patients with suspected epileptic foci refractory to medical management.

METHODS

In the authors’ technique, standard epilepsy evaluation and neuroimaging are used to create a hypothesis-driven SEEG plan, which informs the 3D printing of a novel single-path, multiple-trajectory, omnidirectional platform. Following skull-anchor platform fixation, electrodes are sequentially inserted according to the preoperative plan. The authors describe their surgical experience and technique based on a review of all cases, adult and pediatric, in which patients underwent invasive epilepsy monitoring via SEEG during an 18-month period at Vanderbilt University Medical Center. Platform and anatomical variables influencing localization error were evaluated using multivariate linear regression.

RESULTS

Using this novel technology, 137 electrodes were inserted in 15 patients with focal epilepsy with favorable recording results and no clinical complications. The mean entry point localization error was 1.42 mm (SD 0.98 mm), and the mean target point localization error was 3.36 mm (SD 2.68 mm). Platform distance, electrode trajectory angle, and intracranial distance, but not skull thickness, were independently associated with localization error.

CONCLUSIONS

The multiple-trajectory, single-path, omnidirectional platform offers satisfactory accuracy and favorable clinical results, while avoiding cumbersome frames and prohibitive up-front costs associated with other SEEG technologies.

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David A. Sun, Hong Yu, John Spooner, Armanda D. Tatsas, Thomas Davis, Ty W. Abel, Chris Kao and Peter E. Konrad

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a clinically effective neurosurgical treatment for Parkinson disease. Tissue reaction to chronic DBS therapy and the definitive location of active stimulation contacts are best studied on a postmortem basis in patients who have undergone DBS. The authors report the postmortem analysis of STN DBS following 5 years and 11 months of effective chronic stimulation including the histologically verified location of the active contacts associated with bilateral implants. They also describe tissue response to intraoperative test passes with recording microelectrodes and stimulating semimacroelectrodes. The results indicated that 1) the neural tissue surrounding active and nonactive contacts responds similarly, with a thin glial capsule and foreign-body giant cell reaction surrounding the leads as well as piloid gliosis, hemosiderin-laden macrophages, scattered lymphocytes, and Rosenthal fibers; 2) there was evidence of separate tracts in the adjacent tissue for intraoperative microelectrode and semimacroelectrode passes together with reactive gliosis, microcystic degeneration, and scattered hemosiderin deposition; and 3) the active contacts used for ~ 6 years of effective bilateral DBS therapy lie in the zona incerta, just dorsal to the rostral STN. To the authors' knowledge, the period of STN DBS therapy herein described for Parkinson disease and subjected to postmortem analysis is the longest to date.

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Chris Kao, Jonathan A. Forbes, Walter J. Jermakowicz, David A. Sun, Brandon Davis, Jiepei Zhu, Andre H. Lagrange and Peter E. Konrad

Object

Traumatic brain injury (TBI) often causes an encephalopathic state, corresponding amplitude suppression, and disorganization of electroencephalographic activity. Clinical recovery in patients who have suffered TBI varies, and identification of patients with a poor likelihood of functional recovery is not always straightforward. The authors sought to investigate temporal patterns of electrophysiological recovery of neuronal networks in an animal model of TBI. Because thalamocortical circuit function is a critical determinant of arousal state, as well as electroencephalography organization, these studies were performed using a thalamocortical brain slice preparation.

Methods

Adult rats received a moderate parietal fluid-percussion injury and were allowed to survive for 1 hour, 2 days, 7 days, or 15 days prior to in vitro electrophysiological recording. Thalamocortical brain slices, 450-μm thick, were prepared using a cutting angle that preserved reciprocal connections between the somatosensory cortex and the ventrobasal thalamic complex.

Results

Extracellular recordings in the cortex of uninjured control brain slices revealed spontaneous slow cortical oscillations (SCOs) that are blocked by (2R)-amino-5-phosphonovaleric acid (50 μM) and augmented in low [Mg2+]o. These oscillations have been shown to involve simultaneous bursts of activity in both the cortex and thalamus and are used here as a metric of thalamocortical circuit integrity. They were absent in 84% of slices recorded at 1 hour postinjury, and activity slowly recovered to approximate control levels by Day 15. The authors next used electrically evoked SCO-like potentials to determine neuronal excitability and found that the maximum depression occurred slightly later, on Day 2 following TBI, with only 28% of slices showing evoked activity. In addition, stimulus intensities needed to create evoked SCO activity were elevated at 1 hour, 2 days, and 7 days following TBI, and eventually returned to control levels by Day 15. The SCO frequency remained low throughout the 15 days following TBI (40% of control by Day 15).

Conclusions

The suppression of cortical oscillatory activity following TBI observed in the rat model suggests an injury-induced functional disruption of thalamocortical networks that gradually recovers to baseline at approximately 15 days postinjury. The authors speculate that understanding the processes underlying disrupted thalamocortical circuit function may provide important insights into the biological basis of altered consciousness following severe head injury. Moreover, understanding the physiological basis for this process may allow us to develop new therapies to enhance the rate and extent of neurological recovery following TBI.