Novel intraoperative online functional mapping of somatosensory finger representations for targeted stimulating electrode placement: technical note.

Defining eloquent cortex intraoperatively, traditionally performed by neurosurgeons to preserve patient function, can now help target electrode implantation for restoring function. Brain-machine interfaces (BMIs) have the potential to restore upper-limb motor control to paralyzed patients but require accurate placement of recording and stimulating electrodes to enable functional control of a prosthetic limb. Beyond motor decoding from recording arrays, precise placement of stimulating electrodes in cortical areas associated with finger and fingertip sensations allows for the delivery of sensory feedback that could improve dexterous control of prosthetic hands. In this study, the authors demonstrated the use of a novel intraoperative online functional mapping (OFM) technique with high-density electrocorticography to localize finger representations in human primary somatosensory cortex. In conjunction with traditional pre- and intraoperative targeting approaches, this technique enabled accurate implantation of stimulating microelectrodes, which was confirmed by postimplantation intracortical stimulation of finger and fingertip sensations. This work demonstrates the utility of intraoperative OFM and will inform future studies of closed-loop BMIs in humans.

Recruiting Medical Students to Neurosurgery Through a Focused Neuroanatomy Lab Initiative.

OBJECTIVE: Many medical students find neurosurgery interesting, but few pursue it as a career. Reasons for this mismatch include lack of exposure and poor perceptions of its career demands, work-life balance, personalities, and patient outcomes. It is imperative to recruit promising students early in medical school to build a pipeline of future neurosurgeons. We aimed to recruit medical students to neurosurgery and improve perceptions of the field by hosting an optional cadaver laboratory event (Neuroanatomy Lab Initiative [NLI]) during first-year students' gross anatomy course. METHODS: Five neurosurgery residents and a rotating faculty member led students through the hands-on performance of a retrosigmoid craniotomy on 4 anatomic specimens in the students' cadaveric laboratory. Questionnaires with 6-point Likert scores were distributed to students before and after the NLI. RESULTS: Thirty-nine students with broad specialty interests and previous experiences attended. They perceived neurosurgery to be demanding, competitive, and incongruent with work-life balance and family. At baseline, their interest in neurosurgery was high despite perceived lack of knowledge about the field. Students were eager to participate in neurosurgical procedures and interactions with neurosurgeons. After the NLI, students felt more knowledgeable about neurosurgery and perceived neurosurgery faculty and residents as more pleasant/friendly, approachable, and satisfied with their careers. CONCLUSIONS: An NLI during first-year medical students' anatomy course was an effective, relatively low-resource means of engaging students and improving their perceptions of neurosurgery. We provide a framework for scaling this initiative to other institutions to help recruit the next generation of neurosurgeons.

MR-Guided Functional Neurosurgery: Laser Ablation and Deep Brain Stimulation.

Intraoperative magnetic resonance imaging (iMRI) is increasingly implemented for image-guided procedures in functional neurosurgery. iMRI facilitates accurate electrode implantation for deep brain stimulation (DBS) and is currently an alternative method for DBS electrode targeting. The application of iMRI also allows for greater accuracy and precision in laser-induced thermal therapy (LITT). The expanding use of functional neurosurgical procedures makes safety and feasibility of iMRI important considerations, particularly in patients with comorbidities or complex medical histories. We review here the applications of iMRI and discuss its safety, feasibility, and limitations in functional neurosurgery.To motivate discussion of this topic, we also present a 52-year-old patient with an implanted cardioverter-defibrillator (ICD) who successfully underwent iMRI-guided DBS electrode implantation for advanced Parkinson disease (PD). Neither iMRI nor the passage of electrical current through the implanted DBS electrodes demonstrated detectable interference in ICD function. This case demonstrates that, even in complex clinical contexts, iMRI is a promising tool that merits further exploration for procedures requiring highly accurate and precise identification of target structures.

Direct, intraoperative observation of ~0.1 Hz hemodynamic oscillations in awake human cortex: implications for fMRI.

An almost sinusoidal, large amplitude ~0.1 Hz oscillation in cortical hemodynamics has been repeatedly observed in species ranging from mice to humans. However, the occurrence of 'slow sinusoidal hemodynamic oscillations' (SSHOs) in human functional magnetic resonance imaging (fMRI) studies is rarely noted or considered. As a result, little investigation into the cause of SSHOs has been undertaken, and their potential to confound fMRI analysis, as well as their possible value as a functional biomarker has been largely overlooked. Here, we report direct observation of large-amplitude, sinusoidal ~0.1 Hz hemodynamic oscillations in the cortex of an awake human undergoing surgical resection of a brain tumor. Intraoperative multispectral optical intrinsic signal imaging (MS-OISI) revealed that SSHOs were spatially localized to distinct regions of the cortex, exhibited wave-like propagation, and involved oscillations in the diameter of specific pial arterioles, indicating that the effect was not the result of systemic blood pressure oscillations. fMRI data collected from the same subject 4 days prior to surgery demonstrates that ~0.1 Hz oscillations in the BOLD signal can be detected around the same region. Intraoperative optical imaging data from a patient undergoing epilepsy surgery, in whom sinusoidal oscillations were not observed, is shown for comparison. This direct observation of the '0.1 Hz wave' in the awake human brain, using both intraoperative imaging and pre-operative fMRI, confirms that SSHOs occur in the human brain, and can be detected by fMRI. We discuss the possible physiological basis of this oscillation and its potential link to brain pathologies, highlighting its relevance to resting-state fMRI and its potential as a novel target for functional diagnosis and delineation of neurological disease.

Features and timing of the response of single neurons to novelty in the substantia nigra.

Substantia nigra neurons are known to play a key role in normal cognitive processes and disease states. While animal models and neuroimaging studies link dopamine neurons to novelty detection, this has not been demonstrated electrophysiologically in humans. We used single neuron extracellular recordings in awake human subjects undergoing surgery for Parkinson disease to characterize the features and timing of this response in the substantia nigra. We recorded 49 neurons in the substantia nigra. Using an auditory oddball task, we showed that they fired more rapidly following novel sounds than repetitive tones. The response was biphasic with peaks at approximately 250 ms, comparable to that described in primate studies, and a second peak at 500 ms. This response was primarily driven by slower firing neurons as firing rate was inversely correlated to novelty response. Our data provide human validation of the purported role of dopamine neurons in novelty detection and suggest modifications to proposed models of novelty detection circuitry.

De novo glioblastoma in the territory of a prior middle cerebral artery infarct.

We report a case of a patient who developed glioblastoma in the territory of a previous infarction. Two years after an ischemic stroke, the patient presented with a cystic, necrotic, and heterogeneously enhancing mass. Open biopsy and debulking of the mass with histological analysis revealed the mass to be glioblastoma. Though several cases of posttraumatic GBM have been reported, this is the first proposed case of GBM after an ischemic stroke. From this case, we suggest that the ischemic stroke, like other forms of cortical injury, may predispose to glioblastoma formation.

Management of intracranial hemorrhage in a child with a left ventricular assist device.

Pediatric patients bridged to heart transplant with LVADs require chronic anticoagulation and are at increased risk of hemorrhagic complications, including intracranial hemorrhage. In this population, intracranial hemorrhage is often fatal. We report a case of successful management of a five-yr-old-boy with DCM on an LVAD who developed a subdural hematoma. We initially chose medical management, weighing the patient's high risk of thromboembolism from anticoagulation reversal against the risk of his chronic subdural hematoma. When head CT showed expansion of the hemorrhage with increasing midline shift, we chose prompt surgical evacuation of the hematoma with partial reversal of anticoagulation, given the increased risk of acute deterioration. The patient ultimately received an orthotopic heart transplant and was discharged with no permanent neurological complications. This represents a case of a pediatric patient on an LVAD who survived a potentially fatal subdural hematoma and was successfully bridged to cardiac transplantation.

Efficacy of facial nerve-sparing approach in patients with vestibular schwannomas.

OBJECT: The goal of this article was to show that a combination of facial nerve-sparing microsurgical resection and Gamma Knife surgery (GKS) for expansion of any residual tumor can preserve good facial nerve function in patients with recurrent vestibular schwannoma (VS). METHODS: Records of individuals treated by a single surgeon with a facial nerve-sparing technique for a VS between 1998 and 2009 were retrospectively analyzed for tumor recurrence. Of the 383 patients treated for VS, 151 underwent microsurgical resection, and 20 (13.2%) of these patients required postoperative retreatment for a significant expansion of residual tumor after microsurgery. These 20 patients were re-treated with GKS. RESULTS: The rate of preservation of good facial nerve function (Grade I or II on the House-Brackmann scale) in patients treated with microsurgery for VS was 97%. Both subtotal and gross-total resection had excellent facial nerve preservation rates (97% vs 96%), although subtotal resection carried a higher risk that patients would require retreatment. In patients re-treated with GKS after microsurgery, the rate of facial nerve preservation was 95%. CONCLUSIONS: In patients with tumors that cannot be managed with radiosurgery alone, a facial nerve-sparing resection followed by GKS for any significant regrowth provides excellent facial nerve preservation rates.

Synthesis with structural and electronic characterization of homoleptic Fe(II)- and Fe(III)-fluorinated phenolate complexes.

Four Fe(III) compounds and one Fe(II) compound containing mononuclear, homoleptic, fluorinated phenolate anions of the form [Fe(OAr)(m)](n-) have been prepared in which Ar(F) = C(6)F(5) and Ar' = 3,5-C(6)(CF(3))(2)H(3): (Ph(4)P)(2)[Fe(OAr(F))(5)], 1, (Me(4)N)(2)[Fe(OAr(F))(5)], 2, {K(18-crown-6)}(2)[Fe(OAr(F))(5)], 3a, {K(18-crown-6)}(2)[Fe(OAr')(5)], 3b, and {K(18-crown-6)}(2)[Fe(OAr(F))(4)], 6. Two dinuclear Fe(III) compounds have also been prepared: {K(18-crown-6)}(2)[(OAr(F))(3)Fe(µ(2)-O)Fe(OAr(F))(3)], 4, and {K(18-crown-6)}(2)[(OAr(F))(3)Fe(µ(2)-OAr(F))(2)Fe(OAr(F))(3)], 5. These compounds have been characterized with UV-vis spectroscopy, elemental analysis, Evans method susceptibility, and X-ray crystallography. All-electron, geometry-optimized DFT calculations on four [Ti(IV)(OAr)(4)] and four [Fe(III)(OAr)(4)](-) species (Ar = 2,3,5,6-C(6)Me(4)H, C(6)H(5), 2,4,6-C(6)Cl(3)H(2), C(6)F(5)) with GGA-BP and hybrid B3LYP basis sets demonstrated that, under D(2d) symmetry, π donation from the O 2p orbitals is primarily into the d(xy) and d(z(2)) orbitals. The degree of donation is qualitatively consistent with expectations based on ligand Brønsted basicity and supports the contention that fluorinated phenolate ligands facilitate isolation of nonbridged homoleptic complexes due to their reduced π basicity at oxygen.