Reversal of attenuation of cerebrovascular reactivity to hypercapnia by a nitric oxide donor after controlled cortical impact in a rat model of traumatic brain injury

Functional connectivity, tissue microstructure and T2 at 11.1 Tesla distinguishes neuroadaptive differences in two traumatic brain injury models in rats: A Translational Outcomes Project in NeuroTrauma (TOP-NT) UG3 phase study

The damage caused by contusive traumatic brain injuries (TBIs) is thought to involve breakdown in neuronal communication through focal and diffuse axonal injury along with alterations to the neuronal chemical environment, which adversely affects neuronal networks beyond the injury epicenter(s). In the present study, functional connectivity along with brain tissue microstructure coupled with T2 relaxometry were assessed in two experimental TBI models in rat, controlled cortical impact (CCI) and lateral fluid percussive injury (LFPI). Rats were scanned on an 11.1 Tesla scanner on days 2 and 30 following either CCI or LFPI. Naive controls were scanned once and used as a baseline comparison for both TBI groups. Scanning included functional magnetic resonance imaging (fMRI), diffusion weighted images (DWI), and multi-echo T2 images. fMRI scans were analyzed for functional connectivity across laterally and medially located region of interests (ROIs) across the cortical mantle, hippocampus, and dorsal striatum. DWI scans were processed to generate maps of fractional anisotropy, mean, axial, and radial diffusivities (FA, MD, AD, RD). The analyses focused on cortical and white matter (WM) regions at or near the TBI epicenter. Our results indicate that rats exposed to CCI and LFPI had significantly increased contralateral intra-cortical connectivity at 2 days post-injury. This was observed across similar areas of the cortex in both groups. The increased contralateral connectivity was still observed by day 30 in CCI, but not LFPI rats. Although both CCI and LFPI had changes in WM and cortical FA and diffusivities, WM changes were most predominant in CCI and cortical changes in LFPI. Our results provide support for the use of multimodal MR imaging for different types of contusive and skull-penetrating injury.

The Nociceptin/Orphanin FQ peptide receptor antagonist, SB-612111, improves cerebral blood flow in a rat model of traumatic brain injury

Traumatic brain injury (TBI) affects more than 2.5 million people in the U.S. each year and is the leading cause of death and disability in children and adults ages 1 to 44. Approximately 90% of TBI cases are classified as mild but may still lead to acute detrimental effects such as impaired cerebral blood flow (CBF) that result in prolonged impacts on brain function and quality of life in up to 15% of patients. We previously reported that nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor antagonism reversed mild blast TBI-induced vestibulomotor deficits and prevented hypoxia. To explore mechanisms by which the NOP receptor-N/OFQ pathway modulates hypoxia and other TBI sequelae, the ability of the NOP antagonist, SB-612111 (SB), to reverse TBI-induced CBF and associated injury marker changes were tested in this study. Male Wistar rats randomly received sham craniotomy or craniotomy + TBI via controlled cortical impact. Injury severity was assessed after 1 h (modified neurological severity score (mNSS). Changes in CBF were assessed 2 h post-injury above the exposed cortex using laser speckle contrast imaging in response to the direct application of increasing concentrations of vehicle or SB (1, 10, and 100 µM) to the brain surface. TBI increased mNSS scores compared to baseline and confirmed mild TBI (mTBI) severity. CBF was significantly impaired on the ipsilateral side of the brain following mTBI, compared to contralateral side and to sham rats. SB dose-dependently improved CBF on the ipsilateral side after mTBI compared to SB effects on the respective ipsilateral side of sham rats but had no effect on contralateral CBF or in uninjured rats. N/OFQ levels increased in the cerebral spinal fluid (CSF) following mTBI, which correlated with the percent decrease in ipsilateral CBF. TBI also activated ERK and cofilin within 3 h post-TBI; ERK activation correlated with increased CSF N/OFQ. In conclusion, this study reveals a significant contribution of the N/OFQ-NOP receptor system to TBI-induced dysregulation of cerebral vasculature and suggests that the NOP receptor should be considered as a potential therapeutic target for TBI.

Transient Global Amnesia: An Electrophysiological Disorder Based on Cortical Spreading Depression-Transient Global Amnesia Model

Transient global amnesia (TGA) is a benign memory disorder with etiologies that have been debated for a long time. The prevalence of stressful events before a TGA attack makes it hard to overlook these precipitating factors, given that stress has the potential to organically effect the brain. Cortical spreading depression (CSD) was proposed as a possible cause decades ago. Being a regional phenomenon, CSD seems to affect every aspect of the micro-mechanism in maintaining the homeostasis of the central nervous system (CNS). Corresponding evidence regarding hemodynamic and morphological changes from TGA and CSD have been accumulated separately, but the resemblance between the two has not been systematically explored so far, which is surprising especially considering that CSD had been confirmed to cause secondary damage in the human brain. Thus, by deeply delving into the anatomic and electrophysiological properties of the CNS, the CSD-TGA model may render insights into the basic pathophysiology behind the façade of the enigmatic clinical presentation.

Exposure to Blast Overpressure Impairs Cerebral Microvascular Responses and Alters Vascular and Astrocytic Structure

Exposure to blast overpressure may result in cerebrovascular impairment, including cerebral vasospasm. The mechanisms contributing to this vascular response are unclear. The aim of this study was to evaluate the relationship between blast and functional alterations of the cerebral microcirculation and to investigate potential underlying changes in vascular microstructure. Cerebrovascular responses were assessed in sham- and blast-exposed male rats at multiple time points from 2 h through 28 days after a single 130-kPa (18.9-psi) exposure. Pial microcirculation was assessed through a cranial window created in the parietal bone of anesthetized rats. Pial arteriolar reactivity was evaluated in vivo using hypercapnia, barium chloride, and serotonin. We found that exposure to blast leads to impairment of arteriolar reactivity >24 h after blast exposure, suggesting delayed injury mechanisms that are not simply attributed to direct mechanical deformation. Observed vascular impairment included a reduction in hypercapnia-induced vasodilation, increase in barium-induced constriction, and reversal of the serotonin effect from constriction to dilation. A reduction in vascular smooth muscle contractile proteins consistent with vascular wall proliferation was observed, as well as delayed reduction in nitric oxide synthase and increase in endothelin-1 B receptors, mainly in astrocytes. Collectively, the data show that exposure to blast results in delayed and prolonged alterations in cerebrovascular reactivity that are associated with changes in the microarchitecture of the vessel wall and astrocytes. These changes may contribute to long-term pathologies involving dysfunction of the neurovascular unit, including cerebral vasospasm.

Altered hypermetabolic response to cortical spreading depolarizations after traumatic brain injury in rats

Spreading depolarizations are waves of near-complete breakdown of neuronal transmembrane ion gradients, free energy starving, and mass depolarization. Spreading depolarizations in electrically inactive tissue are associated with poor outcome in patients with traumatic brain injury. Here, we studied changes in regional cerebral blood flow and brain oxygen (PbtO2), glucose ([Glc]b), and lactate ([Lac]b) concentrations in rats, using minimally invasive real-time sensors. Rats underwent either spreading depolarizations chemically triggered by KCl in naïve cortex in absence of traumatic brain injury or spontaneous spreading depolarizations in the traumatic penumbra after traumatic brain injury, or a cluster of spreading depolarizations triggered chemically by KCl in a remote window from which spreading depolarizations invaded penumbral tissue. Spreading depolarizations in noninjured cortex induced a hypermetabolic response characterized by a decline in [Glc]b and monophasic increases in regional cerebral blood flow, PbtO2, and [Lac]b, indicating transient hyperglycolysis. Following traumatic brain injury, spontaneous spreading depolarizations occurred, causing further decline in [Glc]b and reducing the increase in regional cerebral blood flow and biphasic responses of PbtO2 and [Lac]b, followed by prolonged decline. Recovery of PbtO2 and [Lac]b was significantly delayed in traumatized animals. Prespreading depolarization [Glc]b levels determined the metabolic response to clusters. The results suggest a compromised hypermetabolic response to spreading depolarizations and slower return to physiological conditions following traumatic brain injury-induced spreading depolarizations.

The continuum of spreading depolarizations in acute cortical lesion development: Examining Leão's legacy

A modern understanding of how cerebral cortical lesions develop after acute brain injury is based on Aristides Leão's historic discoveries of spreading depression and asphyxial/anoxic depolarization. Treated as separate entities for decades, we now appreciate that these events define a continuum of spreading mass depolarizations, a concept that is central to understanding their pathologic effects. Within minutes of acute severe ischemia, the onset of persistent depolarization triggers the breakdown of ion homeostasis and development of cytotoxic edema. These persistent changes are diagnosed as diffusion restriction in magnetic resonance imaging and define the ischemic core. In delayed lesion growth, transient spreading depolarizations arise spontaneously in the ischemic penumbra and induce further persistent depolarization and excitotoxic damage, progressively expanding the ischemic core. The causal role of these waves in lesion development has been proven by real-time monitoring of electrophysiology, blood flow, and cytotoxic edema. The spreading depolarization continuum further applies to other models of acute cortical lesions, suggesting that it is a universal principle of cortical lesion development. These pathophysiologic concepts establish a working hypothesis for translation to human disease, where complex patterns of depolarizations are observed in acute brain injury and appear to mediate and signal ongoing secondary damage.

Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature

Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

The role of the nitric oxide pathway in brain injury and its treatment--from bench to bedside

Nitric oxide (NO) is a key signalling molecule in the regulation of cerebral blood flow. This review summarises current evidence regarding the role of NO in the regulation of cerebral blood flow at rest, under physiological conditions, and after brain injury, focusing on subarachnoid haemorrhage, traumatic brain injury, and ischaemic stroke and following cardiac arrest. We also review the role of NO in the response to hypoxic insult in the developing brain. NO depletion in ischaemic brain tissue plays a pivotal role in the development of subsequent morbidity and mortality through microcirculatory disturbance and disordered blood flow regulation. NO derived from endothelial nitric oxide synthase (eNOS) appears to have neuroprotective properties. However NO derived from inducible nitric oxide synthase (iNOS) may have neurotoxic effects. Cerebral NO donor agents, for example sodium nitrite, appear to replicate the effects of eNOS derived NO, and therefore have neuroprotective properties. This is true in both the adult and immature brain. We conclude that these agents should be further investigated as targeted pharmacotherapy to protect against secondary brain injury.

Real-time optical diagnosis of the rat brain exposed to a laser-induced shock wave: observation of spreading depolarization, vasoconstriction and hypoxemia-oligemia

Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3-4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.

Stereotactic radiosurgery for trigeminal schwannomas

PURPOSE

Traditionally trigeminal schwannomas (TS) have been treated microsurgically; however, this is often associated with significant morbidity, and complete excision remains a challenge. Stereotactic radiosurgery (SRS) offers a minimally invasive alternative in treating TS. We report on our cumulative experience of using SRS in the treatment of TS.

MATERIALS AND METHODS

Seventy-four TS patients (four with NF2) were treated with SRS using the Leksell Gamma Knife. Mean age (±1 SD) at treatment was 47.1 (15.5) years with a mean interval between presentation and treatment of 30.9 months. Thirty (40.5%) patients had undergone previous surgery on average 47.3 months prior to SRS. The average target volume was 5.3 cm(3) (range 0.4-19.9 cm(3)) and was treated with a mean prescription dose of 16.4 (3.9) Gy to the tumour margin.

RESULTS

Average follow-up was 48.2 months (range 6-168 months). Tumour size remained static in 58 (78.4%) patients and showed radiological evidence of shrinkage in 11 (14.9%). Tumour progression occurred in five (6.6%) patients on average 40 months after SRS (range 12-108). Progression-free survival (PFS) for all patients was 98.5% at 1 year, 92.7% at 5 years and 79.4% at 10 years. Log-rank analysis indicated a significantly worse outcome for NF2 patients (p = 0.001) who demonstrated a PFS of 100% at 1 year and 50% at 5 years. Seven patients developed adverse radiation effects whilst improvements in pre-treatment cranial nerve dysfunction were achieved in eight patients.

CONCLUSIONS

SRS is an effective treatment option in patients with residual or newly diagnosed TS. In view of the results of this study we would advocate a more front-line role for the Gamma Knife in the treatment of this tumour group.

L-arginine reactivity in cerebral vessels after severe traumatic brain injury

OBJECTIVES

Traumatic brain injury (TBI) causes an early reduction of cerebral blood flow (CBF). The purpose was to study cerebrovascular endothelial function by examining the reactivity of cerebral vessels to L-arginine.

METHODS

Fifty-one patients with severe TBI were prospectively studied by measuring cerebral hemodynamics before and after the administration of L-arginine, 300 mg/kg at 12 hours and at 48 hours after injury. These hemodynamic measurements, using transcranial Doppler techniques, included internal carotid flow volume as an estimate of hemispheric CBF, flow velocity in intracranial vessels, CO(2) reactivity, and dynamic pressure autoregulation using thigh cuff deflation and carotid compression methods. Changes in the hemodynamics with L-arginine administration were analyzed using a general linear mixed model.

RESULTS

L-arginine produced no change in mean arterial pressure, intracranial pressure, or brain oxygenation. Overall, L-arginine induced an 11.3% increase in internal carotid artery flow volume (P=0.0190). This increase was larger at 48 hours than at 12 hours (P=0.0045), and tended to be larger in the less injured hemisphere at both time periods. The response of flow velocity in the intracranial vessels was similar, but smaller differences with administration of L-arginine were observed. There was a significant improvement in CO(2) reactivity with L-arginine, but no change in dynamic pressure autoregulation.

DISCUSSION

The low response of the cerebral vessels to L-arginine at 12 hours post-injury with improvement at 48 hours suggests that dysfunction of cerebrovascular endothelium plays a role in the reduced CBF observed after TBI.

Nonvestibular schwannomas: an evaluation of functional outcome after radiosurgical and microsurgical management

PURPOSE

Nonvestibular cranial nerve schwannomas (NVCNS) are relatively rare tumors. We evaluated our experience with radiosurgical and microsurgical treatment alone and in combination for the management of NVCNS.

METHODS

The charts of 62 patients with NVCNS who were treated between 1993 and 2005 at our institution were reviewed. Patients diagnosed with neurofibromatosis type 2 were excluded. The patients underwent microsurgery and/or radiosurgery treatment.

RESULTS

Trigeminal and jugular foramen schwannomas were the most common NVCNS tumors (n = 47), and the only two groups with sufficient numbers of patients to allow comparison of the three treatment approaches. In these two groups, the mean tumor volume was significantly higher in those who received combined therapy (8.59 +/- 2.29 cc), compared with radiosurgery (4.94 +/- 3.02 cc; p = 0.05) or microsurgery alone (5.38 +/- 3.23; p = 0.027). Patients who underwent radiosurgery alone were significantly older (67.7 +/- 13.3 years; p = 0.019) than those treated with microsurgery (55.3 +/- 13.7 years) or with both modalities (48.7 +/- 12.8 years). The Karnofsky Performance Scale scores were significantly higher (p < or = 0.05) at follow-up compared with baseline for all three treatment approaches. There was no significant change in the Glasgow Outcome scores before and after treatment.

CONCLUSIONS

Microsurgery and radiosurgery can both be used to manage NVCNS tumors with excellent results. When treatment with either modality alone is not reasonable, tumors can be managed effectively with combined micro- and radiosurgery treatment.

Mechanisms involved in the cerebrovascular dilator effects of cortical spreading depression

Cortical spreading depression (CSD) leads to dramatic changes in cerebral hemodynamics. However, mechanisms involved in promoting and counteracting cerebral vasodilator responses are unclear. Here we review the development and current status of this important field of research especially with respect to the role of perivascular nerves and nitric oxide (NO). It appears that neurotransmitters released from the sensory and the parasympathetic nerves associated with cerebral arteries, and NO released from perivascular nerves and/or parenchyma, promote cerebral hyperemia during CSD. However, the relative contributions of each of these factors vary according to species studied. Related to CSD, axonal and reflex responses involving trigeminal afferents on the pial surface lead to increased blood flow and inflammation of the overlying dura mater. Counteracting the cerebral vascular dilation is the production and release of constrictor prostaglandins, at least in some species, and other possibly yet unknown agents from the vascular wall. The cerebral blood flow response in healthy human cortex has not been determined, and thus it is unclear whether the cerebral oligemia associated with migraines represents the normal physiological response to a CSD-like event or represents a pathological response. In addition to promoting cerebral hyperemia, NO produced during CSD appears to initiate signaling events which lead to protection of the brain against subsequent ischemic insults. In summary, the cerebrovascular response to CSD involves multiple dilator and constrictor factors produced and released by diverse cells within the neurovascular unit, with the contribution of each of these factors varying according to the species examined.

Microsurgical management of 53 jugular foramen schwannomas: lessons learned incorporated into a modified grading system

OBJECT

Due to the proximity and involvement of critical neurovascular structures, the resection of jugular foramen schwannomas can pose a formidable challenge. The authors review their experience in the microsurgical management of jugular foramen schwannomas and propose a modified grading scale to guide surgical management.

METHODS

All jugular foramen schwannoma cases treated by the senior author (T.F.) between 1980 and 2004 were retrospectively reviewed. The average age at presentation, surgical approach, tumor characteristics, cranial nerve (CN) deficits, and tumor recurrence rates were assessed. The authors present the following modified grading scale: Type A, intradural tumors; Type B, dumbbell-shaped tumors; and Type C, triple dumbbell tumors with a high cervical extension.

RESULTS

The authors treated jugular foramen tumors in 129 patients during the study period. Of these, 53 patients (41%) had jugular foramen schwannomas. The mean patient age was 52 years (range 14-74 years); there were 12 male and 41 female patients. The mean follow-up period was 8.4 years. Patients presented most commonly with deficits of the vagus nerve, followed by vestibular/cochlear nerve and glossopharyngeal nerve deficits. Gross-total resection of the tumor was achieved in 48 patients (90.5%). New postoperative paresis in a previously normal CN was not seen; however, worsening of preoperative CN deficits was frequently noted. The highest incidence occurred with the glossopharyngeal and vagus nerves (30%), with 26% of the deficits being permanent. There were no deaths related to surgery in this series. Three patients (5.7%) experienced tumor recurrence.

CONCLUSIONS

The microsurgical resection of jugular foramen schwannomas carries a risk of worsening preoperative CN deficits; however, these are often transient. Based on their experience, the authors have formulated a grading scale that predicts the optimal surgical approach to these lesions. Considerable technical training and microneuroanatomical knowledge of the region is required. The modified grading scale presented facilitates preoperative planning.

Surgical outcomes of lateral approach for jugular foramen schwannoma: postoperative facial nerve and lower cranial nerve functions

The lateral surgical approach to jugular foramen schwannomas (JFS) may result in complications such as temporary facial nerve palsy (FNP) and hearing loss due to the complicated anatomical location. Ten patients with JFS surgically treated by variable methods of lateral approach were retrospectively reviewed with emphasis on surgical methods, postoperative FNP, and lower cranial nerve status. Gross total removal of the tumors was achieved in eight patients. Facial nerves were rerouted at the first genu (1G) in six patients and at the second genu in four patients. FNP of House-Brackmann (HB) grade III or worse developed immediately postoperatively in six patients regardless of the extent of rerouting. The FNP of HB grade III persisted for more than a year in one patient managed with rerouting at 1G. Among the lower cranial nerves, the vagus nerve was most frequently paralyzed preoperatively and lower cranial nerve palsies were newly developed in two patients. The methods of the surgical approach to JFS can be modified depending on the size and location of tumors to reduce injury of the facial nerve and loss of hearing. Careful manipulation and caution are also required for short facial nerve rerouting as well as for long rerouting to avoid immediately postoperative FNP.

Resuscitation from hemorrhagic shock with HBOC-201 in the setting of traumatic brain injury

Outcomes after mild or moderate head trauma are worsened with associated hypotension, and secondary brain injury can be reduced with timely resuscitation. This study was performed to investigate HBOC-201 as a resuscitation therapy in a combined hemorrhagic shock and brain injury model. Anesthetized rats sustained moderate brain injury using a controlled cortical impact device, followed by rapid hemorrhage to a mean arterial pressure of 30 mmHg. After 30 min of hypotension, animals were resuscitated with HBOC-201, autologous shed blood (SB), or lactated Ringer solution (LR). Brain injury was assessed by measurements of cerebral blood flow (CBF) and cerebral vasoreactivity to hypercapnia (CVH) using a laser Doppler flowmeter. Contusion volume was evaluated histologically, and cerebral edema was determined by total water content. The HBOC rats required significantly less resuscitation volume versus LR and SB. The CBF was significantly diminished at 60 min after resuscitation with HBOC (70.1% +/- 3.8% baseline) compared with LR (105.8% +/- 10.1% baseline; P < 0.01) and SB (96.8% +/- 5% baseline; P < 0.05). The CVH was preserved in the HBOC and SB groups. The CVH was significantly diminished compared with baseline in the LR group at 30 min after resuscitation and showed a significant loss compared with HBOC at 60 min after resuscitation. The contusion volume for HBOC (45.1 mm3) and SB (35.1 mm3) was less than LR (63.5 mm3, P < 0.01). Although CBF was diminished after resuscitation in the HBOC group, HBOC-treated animals maintained CVH and experienced significantly smaller contusion volume than those treated with LR. These results suggest that resuscitation with HBOC-201 protects autoregulatory mechanisms and may reduce secondary brain injury in traumatic brain injury.

Penetrating ballistic-like brain injury in the rat: differential time courses of hemorrhage, cell death, inflammation, and remote degeneration

Acute and delayed cerebral injury was assessed in a recently developed rat model of a penetrating ballistic-like brain injury (PBBI). A unilateral right frontal PBBI trajectory was used to induce survivable injuries to the frontal cortex and striatum. Three distinct phases of injury progression were observed. Phase I (primary injury, 0-6 h) began with immediate (<5 min) intracerebral hemorrhage (ICH) that reached maximal volumetric size at 6 h (27.0 +/- 2.9 mm(3)). During Phase II (secondary injury, 6-72 h), a core lesion of degenerate neurons surrounding the injury track expanded into peri-lesional areas to reach a maximal volume of 69.9 +/- 6.1 mm(3) at 24 h. The core lesion consisted of predominately necrotic cell death and included marked infiltration of both neutrophils (24 h) and macrophages (72 h). Phase III (delayed degeneration, 3-7 days) involved the degeneration of neurons and fiber tracts remote from the core lesion including the thalamus, internal capsule, external capsule, and cerebral peduncle. Overall, different time courses of hemorrhage, lesion evolution, and inflammation were consistent with complementary roles in injury development and repair, providing key information about these mediators of primary, secondary, and delayed brain injury development. The similarities/differences of PBBI to other focal brain injury models are discussed.

Concurrent Monitoring of Cerebral Electrophysiology and Metabolism after Traumatic Brain Injury: An Experimental and Clinical Study

Multiparameter cerebral monitoring has been widely applied in traumatic brain injury to study posttraumatic pathophysiology and to manage head-injured patients (e.g., combining O(2) and pH sensors with cerebral microdialysis). Because a comprehensive approach towards understanding injury processes will also require functional measures, we have added electrophysiology to these monitoring modalities by attaching a recording electrode to the microdialysis probe. These dual-function (microdialysis/electrophysiology) probes were placed in rats following experimental fluid percussion brain injuries, and in a series of severely head-injured human patients. Electrical activity (cell firing, EEG) was monitored concurrently with microdialysis sampling of extracellular glutamate, glucose and lactate. Electrophysiological parameters (firing rate, serial correlation, field potential occurrences) were analyzed offline and compared to dialysate concentrations. In rats, these probes demonstrated an injury-induced suppression of neuronal firing (from a control level of 2.87 to 0.41 spikes/sec postinjury), which was associated with increases in extracellular glutamate and lactate, and decreases in glucose levels. When placed in human patients, the probes detected sparse and slowly firing cells (mean = 0.21 spike/sec), with most units (70%) exhibiting a lack of serial correlation in the spike train. In some patients, spontaneous field potentials were observed, suggesting synchronously firing neuronal populations. In both the experimental and clinical application, the addition of the recording electrode did not appreciably affect the performance of the microdialysis probe. The results suggest that this technique provides a functional monitoring capability which cannot be obtained when electrophysiology is measured with surface or epidural EEG alone.

Transjugular Craniotomy for the Management of Jugular Foramen Tumors with Intracranial Extension

OBJECTIVES

To elucidate indications and outcomes with the transjugular craniotomy for resection of jugular foramen tumors with intracranial extension. The transjugular approach is a lateral craniotomy conducted through a partial petrosectomy traversing the jugular fossa combined with resection of the sigmoid sinus and jugular bulb, which often have been occluded by disease.

STUDY DESIGN

Retrospective review.

SETTING

University medical center.

PATIENTS

Twenty-eight patients with intracranial jugular foramen tumors who underwent a total of 30 surgical procedures.

MAIN OUTCOME MEASURES

Pathologic findings, surgical approach, extent of tumor resection, rate of facial nerve mobilization and ear canal closure, facial and lower cranial nerve outcomes, and hearing preservation.

RESULTS

Tumors included schwannoma (37%), meningioma (33%), glomus jugulare (23%), and chordoma (7%). The surgical approaches were tailored to maximize functional preservation, and included the transjugular (53%), translabyrinthine (17%), retrosigmoid (10%), and far lateral (7%) craniotomies. Translabyrinthine (3%) or transcondylarfar lateral (3%) approaches were occasionally used in combination with the trans-jugular approach. Most procedures were managed in a single stage (90%), but three patients with massive tumor in the neck required two stages. Microsurgical gross total and near-total tumor removal (37% each) were commonly achieved, although subtotal resections (27%) were occasionally performed. In only a minority of cases was facial nerve mobilization (7%) or ear canal closure (21%) required. If present preoperatively, Grade I facial nerve function was usually maintained (22 of 24 [92%]) and Hearing Class A or B could always be maintained (9 of 9 [100%]). As expected, new lower cranial nerve dysfunction was common (8 of 30 [27%]), although over half of the patients had complete lower nerve palsy preoperatively (16 of 30 [53%]).

CONCLUSION

Most patients with jugular foramen tumors with intracranial extension can be managed with a single-stage transjugular craniotomy. Facial nerve mobilization or ear canal closure is usually not required, permitting conservation of facial function and hearing, when present preoperatively.

Pathophysiology of cerebral ischemia and brain trauma: similarities and differences

Current knowledge regarding the pathophysiology of cerebral ischemia and brain trauma indicates that similar mechanisms contribute to loss of cellular integrity and tissue destruction. Mechanisms of cell damage include excitotoxicity, oxidative stress, free radical production, apoptosis and inflammation. Genetic and gender factors have also been shown to be important mediators of pathomechanisms present in both injury settings. However, the fact that these injuries arise from different types of primary insults leads to diverse cellular vulnerability patterns as well as a spectrum of injury processes. Blunt head trauma produces shear forces that result in primary membrane damage to neuronal cell bodies, white matter structures and vascular beds as well as secondary injury mechanisms. Severe cerebral ischemic insults lead to metabolic stress, ionic perturbations, and a complex cascade of biochemical and molecular events ultimately causing neuronal death. Similarities in the pathogenesis of these cerebral injuries may indicate that therapeutic strategies protective following ischemia may also be beneficial after trauma. This review summarizes and contrasts injury mechanisms after ischemia and trauma and discusses neuroprotective strategies that target both types of injuries.