High-fidelity dendritic sodium spike generation in human layer 2/3 neocortical pyramidal neurons.

Dendritic spikes function as cardinal components of rodent neocortical circuit computations. Recently, the biophysical properties of human pyramidal neurons (PNs) have been reported to be divergent, raising the question of whether dendritic spikes have homologous roles in the human neocortex. To directly address this, we made electrical recordings from the soma and apical dendrites of human and rat layer 2/3 PNs of the temporal cortex. In both species, dendritic excitatory input led to the initiation of sodium-channel-mediated dendritic spikes. Dendritic sodium spikes could be generated across a wide input range, exhibited a similar frequency range of activation, and forward-propagated with high-fidelity to implement stereotyped computations in human and rat PNs. However, the physical expansion and complexification of the apical dendritic trees of human PNs allowed the enriched expression of dendritic spike generation. The computational capacity of human PNs is therefore enhanced by the widespread implementation of a conserved dendritic integration mechanism.

Exophytic Brainstem Cavernoma in the Floor of the Fourth Ventricle Midline Suboccipital Approach: 3-Dimensional Operative Video.

This 3-dimensional operative video covers the suboccipital approach to a brainstem cavernoma of the floor of the fourth ventricle. Brainstem cavernomas are low-flow vascular lesions associated with a 2% to 6% annual bleed rate. Repeated bleeds typically result in progressive neurological deficit, and especially for exophytic lesions surgery may arrest this progression without significantly exacerbating pre-existing deficits. The approach to these lesions may be via any standard skull base approach, dictated in each lesion by the presentation to the pial surface. Here, we describe a suboccipital approach to an exophytic cavernoma of the floor of the fourth ventricle, arising caudal to the medial longitudinal fasciculus and facial colliculus. The 38-yr-old male patient had suffered a stepwise neurological deterioration secondary to repeated bleeds, and complete resection of the cavernoma demonstrated here arrested this progression. The patient has provided signed consent to video acquisition and storage at operation, and to publication of this material.

Dual lumbar bronchogenic and arachnoid cyst presenting with sciatica and left foot drop.

INTRODUCTION: Spinal bronchogenic cysts are rare findings, with only four cases of lumbar bronchogenic cysts reported in the literature. All of these bronchogenic cysts involved the conus medullaris. We present the first case of a lumbar bronchogenic cyst and arachnoid cyst arising from the cauda equina in a 68-year-old male. Uniquely, this bronchogenic cyst also contained components of an arachnoid cyst. METHODS: Magnetic resonance imaging (MRI) demonstrated a compressive cystic lesion at the level of the L3 vertebra splaying the cauda equina. An L3/L4 laminectomy was performed with marsupialisation of the cyst. RESULTS: Histological examination revealed pseudostratified ciliated columnar epithelium confirming the diagnosis of a bronchogenic cyst, as well as a pleated fibrovascular tissue lined by sparsely spaced small monomorphic arachnoidal cells, indicating an arachnoid cyst. CONCLUSION: We demonstrate that bronchogenic cysts can be successfully treated with marsupialisation.

Metastatic Neuroendocrine Carcinoma of Unknown Origin Arising in the Femoral Nerve Sheath.

BACKGROUND: Metastatic neuroendocrine carcinoma of unknown origin is a rare condition, usually presenting with lesions in the liver and/or lung. We present the first reported case of a metastatic neuroendocrine carcinoma of unknown origin arising in the femoral nerve sheath. CASE DESCRIPTION: Magnetic resonance imaging demonstrated what was thought to be a schwannoma in the left femoral nerve sheath in the proximal femoral triangle, immediately inferior to the anterior inferior iliac spine. At the time of operation, the tumor capsule was invading surrounding tissue, as well as three trunks of the femoral nerve. The patient underwent a subtotal resection, preserving the integrity of the residual functioning femoral nerve trunks. Histologic evaluation determined that the tumor had features consistent with a metastatic neuroendocrine carcinoma of unknown primary origin. The patient recovered well postoperatively, and subsequent radiologic evaluation failed to demonstrate a potential primary site. Unfortunately, the patient re-presented with disease progression and was subsequently referred to palliative care. CONCLUSIONS: We recommend that there is a definite role for surgery in the management of solitary neuroendocrine carcinoma of unknown origin.

The surgical learning curve and accuracy of minimally invasive lumbar pedicle screw placement using CT based computer-assisted navigation plus continuous electromyography monitoring - a retrospective review of 627 screws in 150 patients.

OBJECTIVE: This study retrospectively assessed the accuracy of placement of lumbar pedicle screws placed by a single surgeon using a minimally-invasive, intra-operative CT-based computer navigated technique in combination with continuous electromyography (EMG) monitoring. The rates of incorrectly positioned screws were reviewed in the context of the surgeon's experience and learning curve. METHODS: Data was retrospectively reviewed from all consecutive minimally invasive lumbar fusions performed by the primary author over a period of over 4 years from April 2008 until October 2012. All cases that had utilized computer-assisted intra-operative CT-based image guidance and continuous EMG monitoring to guide percutaneous pedicle screw placement were analysed for the rates of malposition of the pedicle screws. Pedicle screw malposition was defined as having occurred if the screw trajectory was adjusted intraoperatively due to positive EMG responses, or due to breach of the pedicle cortex by more than 2mm on intraoperative CT imaging performed at the end of the instrumentation procedure. Further analysis of the data was undertaken to determine if the rates of malposition changed with the surgeon's experience with the technique. RESULTS: Six hundred and twenty-seven pedicle screws were placed in one hundred and fifty patients. The overall rate of intraoperative malposition and subsequent adjustment of pedicle screw placement was 3.8% (24 of 627 screws). Screw malposition was detected by intraoperative CT imaging. Warning of potential screw misplacement was provided by use of the EMG monitoring. With increased experience with the technique, rates of intraoperative pedicle screw malposition were found to decrease from 5.1% of screws in the first fifty patients, to 2.0% in the last 50 patients. Only one screw was suboptimally placed at the end of surgery, which did not result in a neurological deficit. CONCLUSION: The use of CT-based computer-assisted navigation in combination with continuous EMG monitoring during percutaneous transpedicular screw placement results in very low rates of malposition and neural injury that compare favourably with previously reported rates. Pedicle screw placement accuracy continues to improve as the surgeon becomes more experienced with the technique.

Pinless frameless electromagnetic image-guided neuroendoscopy in children.

OBJECTIVES: Frameless imaged-guided neuronavigation is a useful adjunct to neuroendoscopy in paediatric patients, especially those with abnormal or complex ventricular or cyst anatomy. The development of electromagnetic neuronavigation has allowed the use of image-guided navigation in the very young patient in whom rigid fixation in cranial pins is contraindicated. The technique and the authors' experience of its use in a series of paediatric patients are described. MATERIALS AND METHODS: Nineteen paediatric patients were treated with endoscopic surgery at two paediatric neurosurgery centres over a period of 18 months. A total of 29 endoscopic procedures were performed. The cases were reviewed and surgical outcomes assessed. In all of the cases, the goal of surgery was realised successfully at the time of surgery, as confirmed by post-operative imaging. No technical failures were encountered. None of the patients suffered worsened neurological function as a result of their procedures. CONCLUSION: Pinless, frameless electromagnetic neuronavigation was found to be a safe technique that can supplement endoscopic surgery in the very young patient. It allows the use of direct navigation of the endoscope in patients that are unable safely to undergo rigid cranial fixation in pins due to young age or thin skull vaults. This has proven to be a useful adjunct to neuroendoscopy in the subset of infants who have complicated or distorted ventricular anatomy and can improve the safety and accuracy of this type of surgery. It is also an alternative to optical neuronavigation in conjunction with neuroendoscopy in patients of any age.