Jaime R. Lopez

Microsurgical resection of brainstem, thalamic, and basal ganglia angiographically occult vascular malformations.

OBJECTIVE To evaluate the clinical results for patients who underwent resection of angiographically occult vascular malformations (AOVMs) of the brainstem, thalamus, or basal ganglia, successfully resected after it exhibited rebleeding and presented to a pial surface. METHODS Between January 1990 and May 1998, 56 patients with 57 deep AOVMs underwent 63 operations, at Stanford University Medical Center, to treat AOVMs of the brainstem (42 AOVMs), thalamus (5 AOVMs), or basal ganglia (10 AOVMs). The surgical approach was suboccipital midline (27 operations), far lateral suboccipital (10 operations), transsylvian (9 operations), interhemispheric transcallosal or infracallosal (8 operations), infratentorial supracerebellar (6 operations), or subtemporal (3 operations). Four patients experienced recurrent bleeding from the same lesion after surgical resection, requiring a second operation. One patient required a planned second operation, using a different approach, to completely resect the lesion, and one patient underwent two surgical procedures to resect two separate brainstem AOVMs. One patient initially underwent exploration but not resection of her AOVM, because it did not present to a pial or ependymal surface. The AOVM was successfully resected after it exhibited rebleeding and presented to a pial surface. RESULTS The immediate outcomes after surgery were unchanged for 31 patients (55%), worsened for 16 (29%), and improved for 9 (16%). The long-term outcomes were unchanged for 24 patients (43%), compared with their presenting grade, worse for 3 (5%), and improved for 29 (52%). Patients who had undergone previous radiotherapy or radiosurgery to treat these lesions experienced more difficult postoperative courses, and radiation necrosis was observed for two patients. CONCLUSION AOVMs of the brainstem, thalamus, and basal ganglia can be safely removed, with a long-term neurological morbidity rate of only 5% and a complete lesion resection rate of 93% after the initial planned resection. The use of cranial base surgical approaches and intraoperative electrophysiological monitoring contributes to successful clinical outcomes.

Evidence-based guideline update: Intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials: Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology and the American Clinical Neurophysiology Society

Objective: To evaluate whether spinal cord intraoperative monitoring (IOM) with somatosensory and transcranial electrical motor evoked potentials (EPs) predicts adverse surgical outcomes. Methods: A panel of experts reviewed the results of a comprehensive literature search and identified published studies relevant to the clinical question. These studies were classified according to the evidence-based methodology of the American Academy of Neurology. Objective outcomes of postoperative onset of paraparesis, paraplegia, and quadriplegia were used because no randomized or masked studies were available. Results and Recommendations: Four Class I and 8 Class II studies met inclusion criteria for analysis. The 4 Class I studies and 7 of the 8 Class II studies reached significance in showing that paraparesis, paraplegia, and quadriplegia occurred in the IOM patients with EP changes compared with the IOM group without EP changes. All studies were consistent in showing all occurrences of paraparesis, paraplegia, and quadriplegia in the IOM patients with EP changes, with no occurrences of paraparesis, paraplegia, and quadriplegia in patients without EP changes. In the Class I studies, 16%–40% of the IOM patients with EP changes developed postoperative-onset paraparesis, paraplegia, or quadriplegia. IOM is established as effective to predict an increased risk of the adverse outcomes of paraparesis, paraplegia, and quadriplegia in spinal surgery (4 Class I and 7 Class II studies). Surgeons and other members of the operating team should be alerted to the increased risk of severe adverse neurologic outcomes in patients with important IOM changes (Level A).

Evidence-based guideline update: intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials*.

Objective To evaluate whether spinal cord intraoperative monitoring (IOM) with somatosensory and transcranial electrical motor evoked potentials (EPs) predict adverse surgical outcomes. Methods A panel of experts reviewed the results of a comprehensive literature search and identified published studies relevant to the clinical question. These studies were classified according to the evidence-based methodology of the American Academy of Neurology. Objective outcomes of postoperative onset of paraparesis, paraplegia, and quadriplegia were used because no randomized or masked studies were available. Results and Recommendations Four class I and eight class II studies met inclusion criteria for analysis. The four class I studies and seven of the eight class II studies reached significance in showing that paraparesis, paraplegia, and quadriplegia occurred in the IOM patients with EP changes compared with the IOM group without EP change. All studies were consistent in showing all occurrences of paraparesis, paraplegia, and quadriplegia in the IOM patients with EP changes, with no occurrences of paraparesis, paraplegia, and quadriplegia in patients without EP change. In the class I studies, 16% to 40% of the IOM patients with EP changes developed postoperative-onset paraparesis, paraplegia, or quadriplegia. IOM is established as effective to predict an increased risk of the adverse outcomes of paraparesis, paraplegia, and quadriplegia in spinal surgery (four class I and seven class II studies). Surgeons and other members of the operating team should be alerted to the increased risk of severe adverse neurologic outcomes in patients with important IOM changes (level A).

The use of electrophysiological monitoring in the intraoperative management of intracranial aneurysms

OBJECTIVES Somatosensory evoked potentials (SSEPs) and brainstem auditory evoked potentials (BAEPs) have been increasingly utilised during surgery for intracranial aneurysms to identify cerebral ischaemia. Between July 1994 and April 1996, we surgically treated 70 aneurysms in 49 consecutive patients (58 operations) with the aid of intraoperative evoked potential monitoring. This study sought to evaluate the usefulness of SSEP and BAEP monitoring during intracranial aneurysm surgery. METHODS Mean patient age was 51.9 (range 18–79) years. The sizes of the aneurysms were 3–4 mm (15), 5–9 mm (26), 10–14 mm (11), 15–19 mm (seven), 20–24 mm (six), and >25 mm (five). SSEPs were monitored in 58 procedures (100%) and BAEPs in 15 (26%). The neurological status of the patients was evaluated before and after surgery. RESULTS Thirteen of the 58 procedures (22%) monitored with SSEPs had SSEP changes (12 transient, one persistent); 45 (78%) had no SSEP changes. Three of 15 patients (20%) monitored with BAEPs had changes (two transient, one persistent); 12 (80%) had no BAEP changes. Of the 14 patients with transient SSEP or BAEP changes, these changes resolved with adjustment or removal of aneurysm clips (nine), elevating MAP (four), or retractor adjustment (one). Mean time from precipitating event to electrophysiological change was 8.9 minutes (range 3–32), and the mean time for recovery of potentials in patients with transient changes was 20.2 minutes (range 3–60). Clinical outcome was excellent in 39 patients, good in five, and poor in three (two patients died), and was largely related to pretreatment grade. CONCLUSIONS SSEPs and BAEPs are useful in preventing clinical neurological injury during surgery for intracranial aneurysms and in predicting which patients will have unfavourable outcomes.

ACNS Guideline: Transcranial Electrical Stimulation Motor Evoked Potential Monitoring.

Motor evoked potentials (MEPs) are electrical signals recorded from neural tissue or muscle after activation of central motor pathways. They complement other clinical neurophysiology techniques, such as somatosensory evoked potentials (SEPs), in the assessment of the nervous system, especially during intraoperative neurophysiologic monitoring (IONM). Somatosensory evoked potentials directly assess only a part of the spinal cord, the dorsal columns (Emerson, 1988), and also the medial lemniscus, the thalamocortical radiations, and somatosensory cortex. Because they provide indirect surveillance of the motor tracts, their use has been shown to improve neurologic outcomes during spinal surgery (Nuwer et al., 1995). However, SEPs can fail to detect damage to the spinal cord motor pathways when the dorsal columns are spared (Ben-David et al., 1987; Ginsburg et al., 1985; Jones et al., 2003; Krieger et al., 1992; Legatt et al., 2014; Zornow et al., 1990); this led to the development of techniques for directly monitoring the central motor pathways. Most often, this is accomplished using transcranial electrical stimulation (TES) of the brain and recording of evoked neural or myogenic activity caudal to the area that is at risk during surgery (Legatt, 2002). During TES, high-intensity stimuli must be delivered to the scalp to stimulate the brain through the intact skull, with stimulus voltage and current levels far above those used to elicit SEPs. If a craniotomy permits direct stimulation of motor cortex by electrodes placed on the brain surface, low-intensity direct cortical stimulation can also be used to elicit MEPs for IONM (Szelényi et al., 2007b; Taniguchi et al., 1993). Direct cortical stimulation is outside the scope of this guideline, but the recommendations herein for the recording of the MEPs that are elicited by transcranial electrical brain stimulation would also apply to recording of MEPs elicited by direct cortical stimulation. Transcranial magnetic stimulation has also been used to elicit MEPs by inducing electrical current flows within the brain tissue without passing large amounts of current through the scalp. This reduces stimulation of pain fibers in the scalp, skull, and meninges and makes it a practical technique for MEP studies in awake subjects (Chen et al., 2008). However, transcranial magnetic stimulation is not the optimal MEP technique for IONM because of the anesthetic suppression of transcranial magnetic stimulation– MEPs which are generated mainly by eliciting I-waves (see section on Definitions and Physiology, below) and difficulties in maintaining a constant position of the coil relative to the patient’s head (Legatt, 2004). Neither TES with single stimulus pulses nor transcranial magnetic stimulation consistently produces robust myogenic MEPs suitable for IONM. The commercial availability of stimulators that can deliver trains of high-intensity electrical pulses has made reliable MEP monitoring using TES possible in most patients. At this time, the techniques for recording and interpreting TES-MEPs have become sufficiently well established to warrant the formulation of these guidelines. Personnel performing TES-MEP monitoring must be cognizant of the technical challenges and risks of the technique.

The usefulness of electrophysiological monitoring during resection of central nervous system vascular malformations

GOAL The purpose of this study was to evaluate the usefulness of electrophysiological monitoring during the resection of vascular malformations. METHODS Between September 1994 and April 1996, we surgically resected vascular malformations (31 arteriovenous malformations, 22 angiographically occult vascular malformations) from 53 patients (56 procedures) and used intraoperative evoked potential monitoring. Somatosensory evoked potentials (SSEPs) were monitored in 54 procedures (96%), and brain stem auditory evoked potentials (BAEPs) in 17 (30%). The neurological status of the patients was evaluated before and after surgery. FINDINGS Five of the 54 patients (9%) monitored with SSEPs had SSEP changes (4 transient, 1 persistent) coinciding with new clinical neurological deficits in 4 patients (all transient). In all 4 patients who had transient SSEP changes, the changes resolved with adjustment or removal of clips on feeding vessels (2 patients) or with elevating mean arterial pressure (MAP) (2 patients). Forty-seven patients (91%) had neither SSEP or neurological examination alterations. One of 17 patients (6%) monitored with BAEPs had neurological and persistent BAEP changes, 15 (88%) had neither BAEP or neurological changes, and 1 (6%) had a neurological change despite no change in BAEP (false negative). The sensitivity of SSEP and BAEP for predicting a new postoperative deficit (transient or prolonged) in this series was 86% (6/7); specificity was 98% (55/56). Clinical outcome was excellent in 41 patients, good in 11 and poor in 1 (no patients died) and was largely related to pretreatment grade. CONCLUSION SSEPs and BAEPs predict the likelihood of clinical neurological injury during resection of vascular malformations with high sensitivity and specificity and may prove a useful adjunct in treating these lesions.

Wrist hyperextension leads to Median nerve conduction block: Implications for intra-arterial catheter placement

BackgroundIt is common practice to hyperextend the wrist to facilitate insertion of a radial intra-arterial catheter. This position may be maintained for prolonged periods. Although there has been much discussion about optimal patient management to protect the ulnar nerve and brachial plexus, little attention has been paid to the median nerve during wrist hyperextension. The authors report the effects of wrist hyperextension on conduction in the median nerve. MethodsMedian nerve conduction was studied in 12 awake, healthy volunteers using standard nerve conduction tests consisting of the measurement of compound sensory and motor action potentials, as well as their amplitudes and latencies. With the contralateral hand as a control, the right wrist was placed in hyperextension (angled between 65 and 80 degrees), and compound action potentials were recorded to determine the onset and magnitude of effects. Subsequently, the hand was released from hyperextension and recovery was recorded. ResultsIn 83% of subjects, hyperextension resulted in a significant decrease in compound sensory action potential amplitudes, sufficient to qualify as conduction block (16.6% of baseline). The average time to conduction block was 43 ± 13.2 min. All subjects who manifested conduction block showed marked improvement 5 min after release from hyperextension. ConclusionsWrist hyperextension for arterial line placement and stabilization is likely to result in profound impairment of median nerve function. Although the effects were transient in this study, the results suggest that prolonged hyperextension may be associated with significant changes in median nerve conduction. To minimize the chance for nerve injury, the authors recommend that wrists be returned promptly to the neutral position following arterial line placement.

Intraoperative electrical stimulation for identification of cranial nerve nuclei

The purpose of this study was to evaluate the feasibility and usefulness of cranial nerve nuclei monitoring during resection of brainstem cavernous malformations. Eleven patients with brainstem cavernous malformations underwent resection of their malformations utilizing cranial nerve nuclei monitoring. Cranial nerves V and VII were monitored by placing electrodes in muscle groups innervated by these nerves and recording manipulation‐induced neurotonic discharges and triggered electromyographic (EMG) activity, after electrical stimulation of the corresponding brainstem nuclei. Seven of 11 procedures (64%) with cranial nerve nuclei monitoring were noted to have cranial nerve nuclei activity corresponding to manipulation of the nuclei. The cavernous malformation was completely resected in 5 of 7 cases with cranial nerve nuclei activity and in all 4 cases without activity. In the remaining 2 cases, the cavernous malformation was not resected due to the proximity of the monitored cranial nerve nuclei to the cavernous malformation and to increasing neurotonic activity as the cavernous malformation was approached. None of the 11 patients had new permanent postoperative deficits corresponding to the cranial nerve nuclei monitored; 1 patient had a transient partial facial palsy lasting 2 days. Preliminary results indicate that cranial nerve nuclei monitoring proves useful in preserving neurologic function and reducing surgical morbidity during resection of brainstem cavernous malformations, particularly indicating when lesion resection places these nuclei at risk.

Neurophysiologic intraoperative monitoring of pediatric cerebrovascular surgery.

The surgical and endovascular treatment of cerebrovascular disorders (CVDs) in children, such as cerebral arteriovenous malformations, cavernous malformations, and moyamoya disease, have become commonplace and routine in many centers. As in the adult population, these procedures carry the risk of intraoperative cerebral ischemia. Therefore, similar strategies used to reduce the risk of cerebral ischemia in adults should be used in children. Unfortunately, there are no published studies on the intraoperative use of available techniques to identify, prevent, or potentially reverse cerebral ischemia. The goal of this article is to review the neurophysiologic techniques that may be useful and applicable in the surgical and endovascular treatment of pediatric CVDs, to describe the rationale and physiologic basis of their utility, to describe our experience in managing these cases, to present some of our results, and finally, to show the clinical utility of these techniques in the intraoperative management of CVDs.

'Entomopia' A remarkable case of cerebral polyopia

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