Accurate localization of the epileptogenic zone is of paramount importance in epilepsy surgery. Despite the availability of noninvasive structural and functional neuroimaging techniques, invasive monitoring with subdural electrodes is still often indicated in the management of intractable epilepsy. Neuronavigation is widely used to enhance the accuracy of subdural grid placement. It allows accurate implantation of the subdural electrodes based on hypotheses formed as a result of the presurgical workup, and can serve as a helpful tool for resection of the epileptic focus at the time of grid explantation. The authors describe 2 additional simple and practical techniques that extend the usefulness of neuronavigation in patients with epilepsy undergoing monitoring with subdural electrodes. One technique involves using the neuronavigation workstation to merge preimplantation MR images with a postimplantation CT scan to create useful images for accurate localization of electrode locations after implantation. A second technique involves 4 holes drilled at the margins of the craniotomy at the time of grid implantation; these are used as fiducial markers to realign the navigation system to the original registration and allow navigation with the merged image sets at the time of reoperation for grid removal and resection of the epileptic focus. These techniques use widely available commercial navigation systems and do not require additional devices, software, or computer skills. The pitfalls and advantages of these techniques compared to alternatives are discussed.
Roukoz B. Chamoun, Vikram V. Nayar, and Daniel Yoshor
Bradley C. Lega and Daniel Yoshor
✓ Spontaneous cerebral venous sinus thrombosis is a rare problem that may be encountered in patients with underlying thrombophilic disorders. It has also been reported as a postoperative complication following suboccipital, transpetrosal, and transcallosal approaches. The authors report on a 67-year-old man with two prior episodes of lower-extremity deep venous thrombosis who underwent transcallosal resection of a colloid cyst and in whom sagittal sinus thrombosis developed 2 weeks thereafter. Results of a subsequent hematological workup revealed both a factor V Leiden mutation and the presence of antiphospholipid antibodies, two thrombophilic risk factors that likely contributed to the development of delayed postoperative sinus thrombosis. Although the safety of low-molecular-weight heparin (LMWH) after craniotomy has not been established in a randomized, controlled study, there is sufficient evidence to justify its use for prophylactic anticoagulation therapy in patients at high risk for postoperative cerebral venous thrombosis. The authors propose using LMWH prophylaxis in patients with thrombophilic disorders who undergo neurosurgical procedures in proximity to dural sinuses in an effort to prevent catastrophic venous infarction.
Jared Fridley, Jonathan G. Thomas, Jovany Cruz Navarro, and Daniel Yoshor
The treatment of patients with refractory epilepsy has always been challenging. Despite the availability of multiple antiepileptic medications and surgical procedures with which to resect seizure foci, there is a subset of epilepsy patients for whom little can be done. Currently available treatment options for these unfortunate patients include vagus nerve stimulation, the ketogenic diet, and electric stimulation, both direct and indirect, of brain nuclei thought to be involved in epileptogenesis. Studies of electrical stimulation of the brain in epilepsy treatment date back to the early 20th century, beginning with research on cerebellar stimulation. The number of potential targets has increased over the years to include the hippocampus, subthalamic nucleus, caudate nucleus, centromedian nucleus, and anterior nucleus of the thalamus (ANT). Recently the results of a large randomized controlled trial, the electrical Stimulation of the Anterior Nucleus of Thalamus for Epilepsy (SANTE) trial, were published, demonstrating a significant reduction in mean seizure frequency with ANT stimulation. Soon after, in 2011, the results of a second randomized, controlled trial—the NeuroPace RNS trial—were published. The RNS trial examined closed-loop, responsive cortical stimulation of seizure foci in patients with refractory partial epilepsy, again finding significant reduction in seizure frequency. In the present review, the authors examine the modern history of electrical stimulation of the brain for the treatment of epilepsy and discuss the results of 2 important, recently published trials, the SANTE and RNS trials.
Jacob R. Joseph, Ashwin Viswanathan, and Daniel Yoshor
Corpus callosotomy offers useful palliation for selected patients with medically intractable seizures, particularly those with uncontrolled and disabling drop attacks. Here the authors present their technique for performing a corpus callosotomy that allows for complete sectioning of the callosum while avoiding entry into the lateral ventricles. The anatomical basis for the technique is the presence of a definable cleft just ventral to the corpus callosum in the midline, formed by the fusion of the two laminae of the septum pellucidum. This small cleft is typically present even in the absence of a cavum septum pellucidum on MR imaging. The authors have found that dividing the body of the corpus callosum by exploiting the cleft of the septum pellucidum in the absolute midline is a simple and expeditious way to perform a callosotomy without entering the lateral ventricles.
Vikram V. Nayar, Rod Foroozan, Jeffrey S. Weinberg, and Daniel Yoshor
Various transcortical approaches have been described for the resection of tumors that lie in the atrium of the lateral ventricle. An approach through the middle temporal gyrus has a short trajectory to the atrium and can grant early access to the tumor's blood supply, but it typically results in damage to the optic radiations that course lateral to the atrium. Anatomical studies have suggested that an approach inferior to the inferior temporal sulcus would avoid traversing through the optic radiations. The authors describe 2 cases of meningioma in the atrium that were exposed and resected through an incision in the inferior temporal gyrus. They provide data from neuroophthalmological testing that shows full preservation of the visual fields with this approach.
Jared Fridley, Rod Foroozan, Vadim Sherman, Mary L. Brandt, and Daniel Yoshor
The purpose of this study was to review the literature on the effectiveness of bariatric surgery for obese patients with idiopathic intracranial hypertension (IIH) with regard to both symptom resolution and resolution of visual deficits.
The published literature was reviewed using manual and electronic search techniques. Data from each relevant manuscript were gathered, analyzed, and compared. These included demographic data, pre- and postoperative symptoms, pre- and postoperative visual field deficits, bariatric procedure type, absolute weight loss, changes in body mass index, and changes in CSF opening pressure.
Eleven relevant publications (including 6 individual case reports) were found, reporting on a total of 62 patients. The Roux-en-Y gastric bypass was the most common bariatric procedure performed. Fifty-six (92%) of 61 patients with recorded postoperative clinical history had resolution of their presenting IIH symptoms following bariatric surgery. Thirty-four (97%) of 35 patients who had undergone pre- and postoperative funduscopy were found to have resolution of papilledema postoperatively. Eleven (92%) of 12 patients who had undergone pre- and postoperative formal visual field testing had complete or nearly complete resolution of visual field deficits, and the remaining patient had stabilization of previously progressive vision loss. In 13 patients both pre- and postoperative CSF pressures were recorded, with an average postoperative pressure decrease of 254 mm H2O. Changes in weight loss and body mass index varied depending on the reported postoperative follow-up interval.
The published Class IV evidence suggests that bariatric surgery may be an effective treatment for IIH in obese patients, both in terms of symptom resolution and visual outcome. Prospective, controlled studies are necessary for better elucidation of its role.
Daniel Yoshor, William H. Bosking, Bradley C. Lega, Ping Sun, and John H. R. Maunsell
Although subdural electrodes are routinely used to map regional brain function, it is unknown if the presence of these implants hinders local cortical function. The authors used psychophysical methods to measure the effect of uncomplicated electrode implantation on local cortical function.
Local field potentials were used to map receptive fields (RFs) for subdural electrodes that were unilaterally implanted on early visual cortex in 4 patients. After electrode implantation, patients did a task that required them to detect an orientation change in a flashing visual stimulus that was presented either inside the mapped RF or outside the RF in the diametrically opposite portion of the other hemifield. The size of the orientation change was varied to span a wide range of behavioral performance. Psychometric curves were generated by fitting behavioral responses to a logistic function. The threshold was defined as the point at which the fitted function crossed 50% detection.
Data were well fit by the logistic function in all 4 patients for both RF and non-RF conditions. None of the volunteers tested showed a statistically significant difference in detection threshold, reaction time, or in the slope of the psychometric function for stimuli presented inside or outside the RF.
Subdural electrodes implanted for extraoperative monitoring do not impair psychophysical performance for a task based on stimuli lying within the RF for recording electrodes. This finding suggests that these electrodes can be used reliably for accurate assessment of regional neurological function.
Patrick J. Karas, Robert Y. North, Visish M. Srinivasan, Nathan R. Lindquist, K. Kelly Gallagher, Jan-Karl Burkhardt, Daniel Yoshor, and Peter Kan
The classic presentation of a carotid-cavernous fistula (CCF) is unilateral painful proptosis, chemosis, and vision loss. Just as the goal of treatment for a dural arteriovenous fistula (dAVF) is obliteration of the entire fistulous connection and the proximal draining vein, the modern treatment of CCF is endovascular occlusion of the cavernous sinus via a transvenous or transarterial route. Here, the authors present the case of a woman with a paracavernous dAVF mimicking the clinical and radiographic presentation of a CCF. Without any endovascular route available to access the fistulous connection and venous drainage, the authors devised a novel direct hybrid approach by performing an endoscopic endonasal transsphenoidal direct puncture and Onyx embolization of the fistula.
Daniel Yoshor, J. Brett Gentry, Scott A. LeMaire, John Dickerson, John Saul, Alex B. Valadka, and Claudia S. Robertson
✓ The authors describe the case of a 24-year-old man who underwent an L-1 corpectomy for spinal decompression and stabilization following an injury that caused an L-1 burst fracture. Postoperatively, an accumulation of spinal fluid developed in the pleural space, which was refractory to 1 week of thoracostomy tube drainage and lumbar cerebrospinal fluid (CSF) diversion. The authors then initiated a regimen of positive-pressure ventilation in which a bilevel positive airway pressure (PAP) mask was used. After 5 days, the CSF collection in the pleural space resolved. Use of a bilevel PAP mask represents a safe, noninvasive method of reducing the negative intrathoracic pressure that promotes CSF leakage into the pleural cavity and may be a useful adjunct in the treatment of subarachnoid—pleural fistula.
Mark Dannenbaum, Bradley C. Lega, Dima Suki, Richard L. Harper, and Daniel Yoshor
Microvascular decompression (MVD) of the facial nerve is an effective treatment for hemifacial spasm (HFS), but the procedure is associated with a significant risk of complications such as hearing loss and facial weakness. Many surgeons advocate the use of intraoperative brainstem auditory evoked response (BAER) monitoring in an attempt to improve surgical outcomes. The authors critically assessed a large series of patients with HFS who underwent MVD without neurophysiological monitoring.
The authors retrospectively identified 114 consecutive patients, with a history of HFS and without a history of HFS surgery, in whom MVD was performed by a single surgeon without the use of neurophysiological monitoring. Postoperative outcomes were determined by reviewing records and through telephone interviews. At least 1 year of postoperative follow-up data were available for 91 of the 114 patients, and the median follow-up duration in all cases was 8 years (range 3 months–23 years). A Kaplan–Meier analysis showed that 86% of the patients were spasm free at 10 years postoperatively.
There were no surgical deaths or major deficits, and complications included 1 case of postoperative deafness, 1 of permanent subtotal hearing loss, and 10 of delayed facial palsy, 2 of which did not completely resolve at last follow-up. The outcomes, rates of hearing loss, and other complications compared well with those reported in studies in which investigators used intraoperative monitoring.
The results suggest that MVD without neurophysiological monitoring is a safe and effective treatment option in patients with HFS. Although BAER monitoring may be a valuable adjunct to surgery at centers experienced with the modality, the absence of intraoperative monitoring should not prevent neurosurgeons from performing MVD in patients with HFS.