Scanning electron microscopy of chronically implanted intracortical microelectrode arrays in non-human primates.

OBJECTIVE: Signal attenuation is a major problem facing intracortical sensors for chronic neuroprosthetic applications. Many studies suggest that failure is due to gliosis around the electrode tips, however, mechanical and material causes of failure are often overlooked. The purpose of this study was to investigate the factors contributing to progressive signal decline by using scanning electron microscopy (SEM) to visualize structural changes in chronically implanted arrays and histology to examine the tissue response at corresponding implant sites. APPROACH: We examined eight chronically implanted intracortical microelectrode arrays (MEAs) explanted from non-human primates at times ranging from 37 to 1051 days post-implant. We used SEM, in vivo neural recordings, and histology (GFAP, Iba-1, NeuN). Three MEAs that were never implanted were also imaged as controls. MAIN RESULTS: SEM revealed progressive corrosion of the platinum electrode tips and changes to the underlying silicon. The parylene insulation was prone to cracking and delamination, and in some instances the silicone elastomer also delaminated from the edges of the MEA. Substantial tissue encapsulation was observed and was often seen growing into defects in the platinum and parylene. These material defects became more common as the time in vivo increased. Histology at 37 and 1051 days post-implant showed gliosis, disruption of normal cortical architecture with minimal neuronal loss, and high Iba-1 reactivity, especially within the arachnoid and dura. Electrode tracts were either absent or barely visible in the cortex at 1051 days, but were seen in the fibrotic encapsulation material suggesting that the MEAs were lifted out of the brain. Neural recordings showed a progressive drop in impedance, signal amplitude, and viable channels over time. SIGNIFICANCE: These results provide evidence that signal loss in MEAs is truly multifactorial. Gliosis occurs in the first few months after implantation but does not prevent useful recordings for several years. Progressive meningeal fibrosis encapsulates and lifts MEAs out of the cortex while ongoing foreign body reactions lead to progressive degradation of the materials. Long-term impedance drops are due to the corrosion of platinum, cracking and delamination of parylene, and delamination of silicone elastomer. Oxygen radicals released by cells of the immune system likely mediate the degradation of these materials. Future MEA designs must address these problems through more durable insulation materials, more inert electrode alloys, and pharmacologic suppression of fibroblasts and leukocytes.

Dynamic stabilization: a nidus for infection?

INTRODUCTION: Dynamic stabilization offers an adjunct to fusion with motion preservation. In comparison, standard instrumented fusion (if) consists of titanium screws and rods/plates, which do not allow for motion at the level of the fusion. The reported infection rate following a standard if ranges from 0.2% to 7%. METHODS: a retrospective chart review of 142 patients who underwent posterior lumbar stabilization procedures was conducted. Ten patients received dynamic stabilization and 132 patients had a standard if. Rates of infection, requiring hardware removal, were compared between the aforementioned groups. RESULTS: Of the 132 patients undergoing posterior if, three developed a deep wound infection requiring removal of hardware (2.3%). Of the 10 patients undergoing dynamic stabilization, three developed a deep wound infection (30%) with 2 requiring removal of hardware (20%), secondary to persistent deep wound infection or osteomyelitis at the pedicle screw sites. There was a significantly increased risk of deep wound infection (p < 0.0001) with the use of dynamic stabilization compared to standard if. CONCLUSIONS: Our series demonstrates that the infection rate in patients undergoing dynamic stabilization is higher than the infection rate for instrumented fusion without a significant difference in comorbidity scores. We postulate that the polycarbonate urethane spacer acts as a medium for bacteria, whereas the titanium screws and rods are smooth, solid, and inert, resulting in a lower risk of infection.

Metastatic renal cell carcinoma, with a radiographically occult primary tumor, presenting in the operative site of a thoracic meningioma: long-term follow-up: Case report.

Lesions metastatic to the site of a meningioma resection from a different primary tumor are rare. Metastasis of a tumor without a known primary tumor is also rare. Metastasis of a renal cell carcinoma, without an identifiable primary tumor, to the bed of a meningioma resection has not been previously reported. The authors describe the case of a 54-year-old man who presented with decreased sensory and motor function in the lower extremities. He underwent T3-5 laminectomies and gross-total removal of an intradural, extramedullary meningioma. The postoperative course was uneventful, and the patient regained full neurological function. After a 3-year period, he developed progressive upper thoracic pain and lower-extremity paresthesias. Imaging studies showed an epidural mass at the T2-4 levels and what appeared to be blastic involvement of the T2-4 vertebrae. A metastatic workup was negative. Emergency revision laminectomies yielded a fibrous, nonvascular mass. Neuropathology was consistent with metastatic renal cell carcinoma. After 6 months, the patient's symptoms of pain and paresthesias recurred. Repeat excision, with decompression of the spinal cord, revealed tumor cells morphologically and immunophenotypically similar to those obtained from the prior surgery. Cytogenetic analysis confirmed the presence of metastatic renal cell carcinoma. A novel case of an epidural metastatic renal cell carcinoma, of unknown primary origin, in the same operative bed of a previously resected intradural, extramedullary meningioma of the thoracic spine is reported.

Failure mode analysis of silicon-based intracortical microelectrode arrays in non-human primates.

OBJECTIVE: Brain-computer interfaces (BCIs) using chronically implanted intracortical microelectrode arrays (MEAs) have the potential to restore lost function to people with disabilities if they work reliably for years. Current sensors fail to provide reliably useful signals over extended periods of time for reasons that are not clear. This study reports a comprehensive retrospective analysis from a large set of implants of a single type of intracortical MEA in a single species, with a common set of measures in order to evaluate failure modes. APPROACH: Since 1996, 78 silicon MEAs were implanted in 27 monkeys (Macaca mulatta). We used two approaches to find reasons for sensor failure. First, we classified the time course leading up to complete recording failure as acute (abrupt) or chronic (progressive). Second, we evaluated the quality of electrode recordings over time based on signal features and electrode impedance. Failure modes were divided into four categories: biological, material, mechanical, and unknown. MAIN RESULTS: Recording duration ranged from 0 to 2104 days (5.75 years), with a mean of 387 days and a median of 182 days (n = 78). Sixty-two arrays failed completely with a mean time to failure of 332 days (median = 133 days) while nine array experiments were electively terminated for experimental reasons (mean = 486 days). Seven remained active at the close of this study (mean = 753 days). Most failures (56%) occurred within a year of implantation, with acute mechanical failures the most common class (48%), largely because of connector issues (83%). Among grossly observable biological failures (24%), a progressive meningeal reaction that separated the array from the parenchyma was most prevalent (14.5%). In the absence of acute interruptions, electrode recordings showed a slow progressive decline in spike amplitude, noise amplitude, and number of viable channels that predicts complete signal loss by about eight years. Impedance measurements showed systematic early increases, which did not appear to affect recording quality, followed by a slow decline over years. The combination of slowly falling impedance and signal quality in these arrays indicates that insulating material failure is the most significant factor. SIGNIFICANCE: This is the first long-term failure mode analysis of an emerging BCI technology in a large series of non-human primates. The classification system introduced here may be used to standardize how neuroprosthetic failure modes are evaluated. The results demonstrate the potential for these arrays to record for many years, but achieving reliable sensors will require replacing connectors with implantable wireless systems, controlling the meningeal reaction, and improving insulation materials. These results will focus future research in order to create clinical neuroprosthetic sensors, as well as valuable research tools, that are able to safely provide reliable neural signals for over a decade.

Quality of patient education materials for rehabilitation after neurological surgery.

OBJECTIVE: To evaluate the quality of online patient education materials for rehabilitation following neurological surgery. METHODS: Materials were obtained from the National Institute of Neurological Disorders and Stroke (NINDS), U.S. National Library of Medicine (NLM), American Occupational Therapy Association (AOTA), and the American Academy of Orthopaedic Surgeons (AAOS). After removing unnecessary formatting, the readability of each site was assessed using the Flesch Reading Ease and Flesch-Kincaid Grade Level evaluations with Microsoft Office Word software. RESULTS: The average values of the Flesch Reading Ease and Flesch-Kincaid Grade Level were 41.5 and 11.8, respectively, which are well outside the recommended reading levels for the average American. Moreover, no online section was written below a ninth grade reading level. CONCLUSION: Evaluations of several websites from the NINDS, NLM, AOTA, and AAOS demonstrated that their reading levels were higher than that of the average American. Improved readability might be beneficial for patient education. Ultimately, increased patient comprehension may correlate to positive clinical outcomes.

Volumetric trends associated with MRI-guided laser-induced thermal therapy (LITT) for intracranial tumors.

BACKGROUND: MR-guided Laser Induced Thermal Therapy (LITT) is a procedure for intracranial tumors. Minimal data exists regarding post-procedure lesion volume changes. OBJECTIVES: We aim to analyze changes in lesion volume during the post-LITT period using polygonal tracing with fusion. Additionally, we investigated the role of lesion histopathology on LITT parameters and volume dynamics. METHODS: Sixteen patients with intracranial neoplasms received LITT. Using OsiriX DICOM Viewer, three raters computed lesion volumes at the following: pre-ablation (PreA), immediate post-ablation (IPA), 24 hours post-ablation (24PA), and first follow-up post-ablation (FPA), which ranged from 4 to 11 weeks post-ablation. Statistical analyses for volume changes between time points and inter-rater reliability were performed. Additionally, comparisons were made between metastatic versus non-metastatic and small versus large lesions in terms of operative parameters and volume changes. RESULTS: There was an acute increase in volume at IPA with a decrease in size by 24PA. ANOVA among inter-rater datasets showed no significant difference at any time point (highest F(1,15) = 0.225, P > 0.80, for IPA). GLM repeated measures, for Intra-Rater analysis, demonstrated statistically significant differences across time points (lowest F(1,15) = 13.297, P = 0.003). IPA volumes were larger than those at PreA, 24PA, and FPA (average volume increase [95% CI]: 281% [157-404%], 167% [134-201%], 187% [154-219%], respectively; all P < 0.004). Correlation analysis showed lower inter-rater reliability at IPA versus other time points (all P < 0.03). Larger lesions (>2.5 cm³ ) versus smaller (<2.5 cm³ ) did not demonstrate a difference in percent volume increase. Operative parameters and volume dynamics were not different between metastatic and non-metastatic groups. CONCLUSIONS: The response of intracranial lesions to LITT demonstrates a peak in volume at the IPA time point with decreased IPA inter-rater reliability. We recommend that conclusions about intracranial lesion size post-LITT be made at least 24 hours post-LITT rather than immediately after LITT.

Current differential diagnoses and treatment options of vascular occlusions presenting as bilateral thalamic infarcts: a review of the literature.

bilateral thalamic infarctions are rare and usually caused by vascular occlusions. When symptomatic, it is important to make a distinction between different vascular etiologies in order to provide an effective and timely therapeutic response. Clinical presentations may not adequately differentiate between the vascular etiologies alone. It is therefore important to use imaging technologies to distinguish appropriately the origin of the infarct so that proper treatment can be administered. Advanced imaging techniques, such as CT angiography and MR angiography, have proved useful for distinguishing between arterial and venous causes of bithalamic infarctions. Bilateral thalamic venous infarctions can be treated with anticoagulation medication and with thrombolysis in more severe cases. Bilateral thalamic arterial infarctions may be treated with thrombolysis.

Magnetic resonance thermometry-guided laser-induced thermal therapy for intracranial neoplasms: initial experience.

BACKGROUND: Laser-induced thermal therapy is a promising tool in the neurosurgeon's armamentarium. This methodology has seen a resurgence in application as a result of advances in technology. OBJECTIVE: To report our initial experience with the procedure after treating 20 consecutive patients, the largest series to date. METHODS: Patients were selected for laser therapy if they had failed conventional therapies, were unable to tolerate an open cranial procedure, or the tumor was deemed otherwise inoperable. In this series, 980-nm diode laser catheters were placed stereotactically in the operating room. The patients were then transferred to the magnetic resonance imaging suite for thermal ablation. RESULTS: A total of 31 laser applicators were placed in 20 patients with intracranial neoplasms. The majority of patients (17 of 20) had prior treatment for their tumors. The overall accuracy of laser insertion was 83.9%, improving with increased experience. The average lesion volume treated was 7.0 ± 9.0 cm2. With the use of damage estimates from the software provided, the treatment continued until the entire tumor had been irreversibly ablated. The average length of hospitalization was 2.27 days, with the majority of patients going home on postoperative day 1. Complications occurred in 4 patients, typically in those who were in poor health preoperatively. CONCLUSION: Laser-induced thermal therapy is an intuitive procedure for treating difficult intracranial neoplasms. As with any other procedure, patient selection and lesion selection are important factors in determining outcome.

Current therapeutic strategies for inflammation following traumatic spinal cord injury.

Damage from spinal cord injury occurs in two phases - the trauma of the initial mechanical insult and a secondary injury to nervous tissue spared by the primary insult. Apart from damage sustained as a result of direct trauma to the spinal cord, the post-traumatic inflammatory response contributes significantly to functional motor deficits exacerbated by the secondary injury. Attenuating the detrimental aspects of the inflammatory response is a promising strategy to potentially ameliorate the secondary injury, and promote significant functional recovery. This review details how the inflammatory component of secondary injury to the spinal cord can be treated currently and in the foreseeable future.