Stephan J. Goerss

Awake craniotomy for aggressive resection of primary gliomas located in eloquent brain

OBJECTIVEnTo determine with intraoperative neurologic and language examinations the maximal tumor resection achievable with acceptable postoperative neurologic dysfunction in patients undergoing awake stereotactic glial tumor resection in eloquent regions of the brain.nnnPATIENTS AND METHODSnBetween October 1995 and December 2000, 65 patients underwent frameless stereotactic resection of glial tumors located in functioning tissue. During the resection, continuous examinations by a neurologist and speech pathologist were performed. The goal of surgery was to resect the maximum neurologically permissible tumor volume defined on preoperative T2 imaging. Tumor resection was stopped at the onset of neurologic dysfunction. Novel segmentation software was used to measure tumor cytoreduction based on pre- and postoperative magnetic resonance imaging. All patients underwent 3-month postoperative neurologic examinations to determine functional outcomes.nnnRESULTSnThe cortical and subcortical white matter tracts at risk for injury were the left frontal operculum in 15 patients, the central lobule in 38, the insula in 11, and the left angular gyrus in 1. Thirty-four (52%) had a greater than 90% reduction in T2 signal postoperatively. In 26 patients thought to have low-grade tumors based on preoperative imaging, 12 proved to have grade 3 gliomas. Forty-eight patients (74%) developed intraoperative deficits; 34 (71%) recovered to a modified Rankin grade of 0 or 1 at 3 months postoperatively, 11 (23%) achieved a modified Rankin grade of 2, and 3 patients (6%) achieved a modified Rankin grade of 3 or 4 at 3-month follow-up. There was no operative mortality; 17 patients (26%) died from tumor progression during the follow-up period.nnnCONCLUSIONSnCombining frameless computer-guided stereotaxis with cortical stimulation and repetitive neurologic and language assessments facilitates tumor resection in functioning brain regions. Resecting tumor until the onset of neurologic deficits allows for a good functional recovery. Imaging software can objectively and accurately measure preoperative and postoperative tumor volumes.

Results of computed tomography-based computer-assisted stereotactic resection of metastatic intracranial tumors.

Forty-four patients underwent 45 computer-assisted stereotactic resections of intracranial metastases from various centrally located and deep-seated regions using methods described in this report and elsewhere. Gross total removal was achieved in all cases. There was no postoperative mortality (within 30 days). Postoperative neurological examinations revealed that: (a) of 26 who presented with preoperative neurological deficits, 13 were normal postoperatively, 7 were improved, 3 were unchanged, and 3 were worse; (b) 5 of 5 patients who had increased intracranial pressure preoperatively were normal postoperatively; and (c) 3 of 3 patients who had increased intracranial pressure and neurological deficit preoperatively were neurologically normal postoperatively. Nine of 10 patients who were neurologically normal preoperatively were normal postoperatively, and the other had transient upper extremity weakness after resection of a lesion in the contralateral motor strip. The 1-year survival in this group of patients was 62.5%. No local recurrence was noted in any patient. Computer-assisted stereotactic resection permits accurate localization of metastatic lesions and gross total resection from difficult locations with acceptable levels of morbidity.

A computed tomographic stereotactic adaptation system.

An adaptation to render an existing popular stereotactic apparatus compatible with computed tomography (CT) is described. A localization system attaches to the stereotactic head holder and a simple computer program allows considerable accuracy in the translation of CT data into stereotactic space in the operating room.

High frequency stimulation of the subthalamic nucleus evokes striatal dopamine release in a large animal model of human DBS neurosurgery

Subthalamic nucleus deep brain stimulation (STN DBS) ameliorates motor symptoms of Parkinsons disease, but the precise mechanism is still unknown. Here, using a large animal (pig) model of human STN DBS neurosurgery, we utilized fast-scan cyclic voltammetry in combination with a carbon-fiber microelectrode (CFM) implanted into the striatum to monitor dopamine release evoked by electrical stimulation at a human DBS electrode (Medtronic 3389) that was stereotactically implanted into the STN using MRI and electrophysiological guidance. STN electrical stimulation elicited a stimulus time-locked increase in striatal dopamine release that was both stimulus intensity- and frequency-dependent. Intensity-dependent (1-7V) increases in evoked dopamine release exhibited a sigmoidal pattern attaining a plateau between 5 and 7V of stimulation, while frequency-dependent dopamine release exhibited a linear increase from 60 to 120Hz and attained a plateau thereafter (120-240Hz). Unlike previous rodent models of STN DBS, optimal dopamine release in the striatum of the pig was obtained with stimulation frequencies that fell well within the therapeutically effective frequency range of human DBS (120-180Hz). These results highlight the critical importance of utilizing a large animal model that more closely represents implanted DBS electrode configurations and human neuroanatomy to study neurotransmission evoked by STN DBS. Taken together, these results support a dopamine neuronal activation hypothesis suggesting that STN DBS evokes striatal dopamine release by stimulation of nigrostriatal dopaminergic neurons.

Wireless fast-scan cyclic voltammetry to monitor adenosine in patients with essential tremor during deep brain stimulation.

Essential tremor is often markedly reduced during deep brain stimulation simply by implanting the stimulating electrode before activating neurostimulation. Referred to as the microthalamotomy effect, the mechanisms of this unexpected consequence are thought to be related to microlesioning targeted brain tissue, that is, a microscopic version of tissue ablation in thalamotomy. An alternate possibility is that implanting the electrode induces immediate neurochemical release. Herein, we report the experiment performing with real-time fast-scan cyclic voltammetry to quantify neurotransmitter concentrations in human subjects with essential tremor during deep brain stimulation. The results show that the microthalamotomy effect is accompanied by local neurochemical changes, including adenosine release.

Surgical Options for Patients With Deep-Seated Brain Tumors: Computer-Assisted Stereotactic Biopsy

The histologic nature of deep-seated intracranial lesions can be determined by using a computer-assisted stereotactic biopsy technique. The procedures are performed with use of local anesthesia. A data base consisting of stereotactic computed tomographic scans and stereotactic cerebral angiography is acquired. Target coordinates and trajectory approach angles are calculated by using a computer system in the operating room. Since July 1984, 36 patients with a variety of pathologic lesions in various intracranial sites have undergone this procedure at our institution. Of the 36 patients thought to have neoplastic lesions preoperatively, 6 were found to have nonneoplastic lesions, information that was of importance in the therapeutic management of these patients. Of the 30 patients with tumors, 24 had astrocytomas of various grades, 3 had metastatic lesions, and an additional 3 had lymphomas. Computer-assisted stereotactic biopsy with arteriographic control is an accurate and relatively safe method of determining the histologic nature of any suspicious intracranial lesion.

Increased cortical extracellular adenosine correlates with seizure termination.

Seizures are currently defined by their electrographic features. However, neuronal networks are intrinsically dependent on neurotransmitters of which little is known regarding their periictal dynamics. Evidence supports adenosine as having a prominent role in seizure termination, as its administration can terminate and reduce seizures in animal models. Furthermore, microdialysis studies in humans suggest that adenosine is elevated periictally, but the relationship to the seizure is obscured by its temporal measurement limitations. Because electrochemical techniques can provide vastly superior temporal resolution, we test the hypothesis that extracellular adenosine concentrations rise during seizure termination in an animal model and humans using electrochemistry.

Methodology and Clinical Experience with Computed Tomography and a Computer-resident Stereotactic Atlas

We have developed a computer-resident stereotactic atlas of the human brain that quantitatively defines subcortical structures within anatomical landmarks detected on obliquely reconstructed computed tomography (CT) slices. Horizontal stereotactic atlas sections can be stretched and contracted by polar transformation and labeled by a computer to fit within these CT scan-defined landmarks. The stereotactic coordinates of any substructure on the atlas-labeled CT slice may then be calculated by the computer and expressed in mechanical adjustments on a stereotactic surgical frame located in the operating room. We demonstrate the use of this method in the stereotactic treatment of movement disorders as an augmentation to conventional ventriculography and microelectrode recording.

Development of intraoperative electrochemical detection: wireless instantaneous neurochemical concentration sensor for deep brain stimulation feedback

Deep brain stimulation (DBS) is effective when there appears to be a distortion in the complex neurochemical circuitry of the brain. Currently, the mechanism of DBS is incompletely understood; however, it has been hypothesized that DBS evokes release of neurochemicals. Well-established chemical detection systems such as microdialysis and mass spectrometry are impractical if one is assessing changes that are happening on a second-to-second time scale or for chronically used implanted recordings, as would be required for DBS feedback. Electrochemical detection techniques such as fast-scan cyclic voltammetry (FSCV) and amperometry have until recently remained in the realm of basic science; however, it is enticing to apply these powerful recording technologies to clinical and translational applications. The Wireless Instantaneous Neurochemical Concentration Sensor (WINCS) currently is a research device designed for human use capable of in vivo FSCV and amperometry, sampling at subsecond time resolution. In this paper, the authors review recent advances in this electrochemical application to DBS technologies. The WINCS can detect dopamine, adenosine, and serotonin by FSCV. For example, FSCV is capable of detecting dopamine in the caudate evoked by stimulation of the subthalamic nucleus/substantia nigra in pig and rat models of DBS. It is further capable of detecting dopamine by amperometry and, when used with enzyme linked sensors, both glutamate and adenosine. In conclusion, WINCS is a highly versatile instrument that allows near real-time (millisecond) detection of neurochemicals important to DBS research. In the future, the neurochemical changes detected using WINCS may be important as surrogate markers for proper DBS placement as well as the sensor component for a smart DBS system with electrochemical feedback that allows automatic modulation of stimulation parameters. Current work is under way to establish WINCS use in humans.

Magnetic Resonance Imaging-Based Computer-Assisted Stereotactic Resection of the Hippocampus and Amygdala in Patients With Temporal Lobe Epilepsy

In patients with medically intractable complex partial seizures of temporal lobe origin, stereotactic amygdalohippocampectomy can now provide excellent results. Target structures can be accurately identified and completely resected with use of a carbon dioxide laser. In a series of 18 patients who underwent this computer-interactive procedure, all experienced a cessation or dramatic reduction in frequency of seizure activity. Because the inferior optic radiations are disrupted with use of the posterolateral approach, nondisabling postoperative visual field deficits always ensue. In addition, two of our patients who underwent left-sided procedures had transient minor speech problems, perhaps attributable to postoperative swelling of the lateral temporal lobe. Patients in whom a surface electroencephalogram discloses a posterior temporal focus of seizure activity are candidates for stereotactic amygdalohippocampectomy.