Neurofilament-light in former athletes: a potential biomarker of neurodegeneration and progression.

BACKGROUND/OBJECTIVE: This study aimed to evaluate serum neurofilament light chain (NF-L) levels in former professional contact sports athletes with multiple concussions (ExPro) as a potential biomarker of neurodegeneration and predictor of white-matter (WM) abnormality progression. METHODS: Concentrations of NF-L in the serum of fifty-two cognitively normal ExPro and twenty-one healthy controls (HC) with no history of concussions were measured using single molecule array (Simoa) technology. Both groups underwent neuroimaging at the time of serum collection. Eighteen of the participants in the ExPro underwent follow-up imaging after 2 years. RESULTS: Levels of serum NF-L were not significantly different between the ExPro and HC. However, in the ExPro group, NF-L levels were positively correlated with the mean diffusivity (MD) of corpus callosum (CC) and fornix, and total ventricular volume. Moreover, NF-L levels in the ExPro group at the first visit were positively correlated with the amount of increase in CC MD at the 2-year follow-up. CONCLUSIONS: NF-L levels reflect neuronal changes in the ExPro group and predict the extent of decrease in white matter integrity over time. Serum NF-L might be a biomarker of neurodegeneration and WM abnormality progression in ExPro.

Click-crosslinked injectable hyaluronic acid hydrogel is safe and biocompatible in the intrathecal space for ultimate use in regenerative strategies of the injured spinal cord.

Traumatic spinal cord injury (SCI) causes damage and degeneration at and around the lesion site resulting in a loss of function. SCI presents a complex regenerative problem due to the multiple aspects of growth inhibition and the heterogeneity in size, shape and extent of injury. Currently, there is no widely accepted treatment strategy available and delivering biomolecules to the central nervous system remains a challenge. With a view towards achieving local release, we designed a hydrogel that can be injected into the intrathecal space. Here we describe the synthesis and characterization of a click-crosslinked hyaluronic acid hydrogel and demonstrate controlled in vitro release of bioactive brain derived neurotrophic factor. Importantly, we demonstrate that this new hydrogel is both biocompatible in the intrathecal space based on immunohistochemistry of the host tissue response and safe based on behavioral analysis of locomotor function.

Intrathecal transplantation of stem cells by lumbar puncture for thoracic spinal cord injury in the rat.

STUDY DESIGN: Experimental investigation of intrathecal transplantation of stem cells by lumbar puncture (LP) in a rat model that simulates human thoracic spinal cord injury (SCI). OBJECTIVES: To examine the distribution and phenotype of spinal cord-derived neural stem/progenitor cells (NSPCs) and bone marrow-derived mesenchymal stromal cells (BMSCs) following LP transplantation in SCI rats. SETTING: Toronto Western Research Institute, Toronto, Ontario, Canada. METHODS: NSPCs or BMSCs were transplanted via LP at level L3-5 1 week after compression SCI at T8. Rats were killed at 3, 17 and 27 days after LP transplantation and the relative distribution of cells at C4, T8 and L3-5 was quantitated. The phenotype of the NSPC and BMSC was assessed with immunocytochemistry in vitro and following LP transplantation. RESULTS: By 4 weeks, more NSPC migrated to the lesion site relative to BMSC and uninjured animals. However, there was no preferential homing of either of these types of cells into the parenchyma of the injury site, and most of the transplanted cells remained in the intrathecal space. In vitro, spinal cord-derived NSPC proliferated and expressed nestin, but after LP transplantation, NSPC became post-mitotic and primarily expressed oligodendrocyte markers. In contrast, BMSC did not express any neural antigens in vivo. CONCLUSION: LP is a minimally invasive method of cell transplantation that produces wide dissemination of cells in the subarachnoid space of the spinal cord. This is the first study to report and quantify the phenotype and spatial distribution of LP transplanted NSPC and BMSC in the intact and injured spinal cord.

Cell-permeant Ca2+ chelators reduce early excitotoxic and ischemic neuronal injury in vitro and in vivo.

We report the characterization of the first successful treatment of neuronal ischemic injury in vivo by cell-permeant Ca2+ chelators. The chelators attenuated glutamate-induced intracellular Ca2+ increases and neurotoxicity in neuronal explant cultures. When infused intravenously in rats, permeant fluorescent BAPTA analogs accumulated in neurons in several brain regions. BAPTA-AM, infused in vivo, reduced Ca(2+)-dependent spike frequency adaptation and post-spike train hyperpolarizations in CA1 neurons taken from treated animals. This effect was reproduced by direct injections of BAPTA into untreated neurons. The effects of three different chelators (BAPTA, 5,5'-difluoro BAPTA, and 4,4'-difluoro BAPTA) on Ca(2+)-dependent membrane excitability varied with their Ca2+ affinity. When the chelators' permeant forms were used to treat rats prior to the induction of focal cortical ischemia, they were highly neuroprotective, as gauged by significant reductions in cortical infarction volumes and neuronal sparing. The chelators' protective effects in vivo also reflected their affinity for Ca2+. This report provides the most direct evidence to date that intracellular Ca2+ excess triggers early neurodegeneration in vivo and contributes a novel therapeutic approach to neuronal ischemia of potential clinical utility.

Transplanted adult spinal cord-derived neural stem/progenitor cells promote early functional recovery after rat spinal cord injury.

We examined the effect of spinal cord-derived neural stem/progenitor cells (NSPCs) after delayed transplantation into the injured adult rat spinal cord with or without earlier transplantation of bone marrow-derived mesenchymal stromal cells (BMSCs). Either BMSCs or culture medium were transplanted immediately after clip compression injury (27 g force), and then, 9 days after injury, NSPCs or culture medium were transplanted. Cell survival and differentiation, functional recovery, retrograde axonal tracing, and immunoelectron microscopy were assessed. A significant improvement in functional recovery based on three different measures was seen only in the group receiving NSPCs without BMSCs, and the improved recovery was evident within 1 week of transplantation. In this group, NSPCs differentiated mainly into oligodendrocytes and astrocytes, there was ensheathing of axons at the injury site by transplanted NSPCs, an increase in host oligodendrocytes, and a trend toward an increase in retrogradely labeled supraspinal nuclei. Transplantation of the BMSC scaffold resulted in a trend toward improved survival of the NSPCs, but there was no increase in function. Thus, transplantation of adult rat NSPCs produced significant early functional improvement after spinal cord injury, suggesting an early neuroprotective action associated with oligodendrocyte survival and axonal ensheathment by transplanted NSPCs.

Conservative management of vestibular schwannomas: third review of a 10-year prospective study.

Seventy-two patients with a unilateral vestibular schwannoma have been treated conservatively for a median of 121 months. They have been followed prospectively by serial clinical examination, MRI scans and audiometry. Twenty-five patients (35%, 95% CI: 24-47) failed conservative management and required active intervention during the study. No factors predictive of tumour growth or failure of conservative management could be identified. Seventy-five per cent of failures occurred in the first half of the 10-year study. The median growth rate for all tumours at 10 years was 1 mm/year (range -0.53-7.84). Cerebellopontine angle tumours grew faster (1.4 mm/year) than intracanalicular tumours (0 mm/year, P < 0.01); 92% had growth rates under 2 mm/year. Hearing deteriorated substantially even in tumours that did not grow, but did so faster in tumours that grew significantly (mean deterioration in pure tone average at 0.5, 1, 2 and 3 kHz was 36 dB; speech discrimination scores deteriorated by 40%). Patients who failed conservative management had clinical outcomes that were not different from those who underwent primary treatment without a period of conservative management.

Bone marrow-derived mesenchymal stromal cells for the repair of central nervous system injury.

Transplantation of bone marrow-derived mesenchymal stromal cells (MSCs) into the injured brain or spinal cord may provide therapeutic benefit. Several models of central nervous system (CNS) injury have been examined, including that of ischemic stroke, traumatic brain injury and traumatic spinal cord injury in rodent, primate and, more recently, human trials. Although it has been suggested that differentiation of MSCs into cells of neural lineage may occur both in vitro and in vivo, this is unlikely to be a major factor in functional recovery after brain or spinal cord injury. Other mechanisms of recovery that may play a role include neuroprotection, creation of a favorable environment for regeneration, expression of growth factors or cytokines, vascular effects or remyelination. These mechanisms are not mutually exclusive, and it is likely that more than one contribute to functional recovery. In light of the uncertainty surrounding the fate and mechanism of action of MSCs transplanted into the CNS, further preclinical studies with appropriate animal models are urgently needed to better inform the design of new clinical trials.

Retention of tritiated methotrexate in a transplantable mouse glioma.

The uptake and distribution of tritiated methotrexate ([H]MTX) were studied by autoradiography and liquid scintillation countinf for up to 7 days after i.v. injection in mice bearing s.c. or intracerebral (i.c.) implants of a transplantable mouse ependymoblastoma. Autoradiography showed that s.c. tumors took up more [3H]MTX than i.c. tumors. In both s.c. and i.c. tumors, [3H]MTX was mainly intracellular, with very little in intersitial fluid sites. Retention of [3H]MTX gradually diminished with time, with some still being present 7 days after injection. The distribution of [3H]MTX in the i.c. tumors was not uniform, and portions of these tumors were relatively inaccessible to the drug. The uniformity of distribution did not improve with time. Scintillation counting showed that s.c. tumors accumulated much less [3H-A1MTX and retained a lower proportion of [3H]MTX than many normal tissues. These studies indicate that [3H]MTX has 3 major shortcomings as a chemotherapeutic agent for brain tumors. First, the amount of drug taken up by the transplantable mouse ependymoblastoma was small in comparison with normal tissues and in comparison with other agents taken up by this tumor. Second, the distribution of the drug in the i.c. tumors was nonuniform, with tumor cells in certain areas remaining relatively inaccessible to the drug. Last, the retention of the drug in the tumor was far less than in normal tissues.

Glucose analogs as potential diagnostic tracers for brain tumors.

No tumor-specific tracer has yet been found for the detection of brain tumors by external scintiscanning. Glucose is a substrate in high demand by almost all tumors, and therefore an investigation was undertaken into the potential value of glucose and its analogs as tracers for brain tumors. The compounds studied were D-)1-3H)glucose, D-(1-14C)glucose, (3H)3-O-methyl-D-glucose and L-(1-14C)glucose. The tracers were injected i.v. into C57BL/6J mice carrying a transplantable s.c. ependymoblastoma. At specific time intervlas after injection, mice were sacrificed and the radioactivity of 6 tissues including tumor and brain were assayed by means of an automated combustion technique and liquid scintillation counting. Tumor uptake, expressed as percentage mean body concentration, was 60% for 2 of the tracers, and 92 and 143%, respectively, for 2 others. Brain uptake was over 130% mean body concentration, with 3 of the 4 tracers studies. With L-glucose, brain uptake was only 15.4% mean body concentration, and a maximum tumor-to-brain ratio of 9.5 was achieved. The very high tumor uptake achieved with two of these carbohydrated demonstrates that a carbohydrate analog may be found that shows high tumor specificity and uptake, and that may be useful for external scintiscanning.

Use of phenobarbital and high doses of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea in the treatment of brain tumor-bearing mice.

It has been shown that the nitrosoureas are substrates for hepatic microsomal enzymes in vitro and that phenobarbital (PB) administered in multiple doses prior to nitrosourea administration significantly reduces the activity of the nitrosoureas in murine brain tumor models. In the present study, the effect of PB on 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) was assessed by determining the CCNU dose which would result in the long-term survival of 50% of the treated mice, and the CCNU dose which would result in the toxic death of 50% of the treated mice, with or without PB pretreatment in C56BL/6J mice. The therapeutic index, the CCNU dose which would result in the long-term survival of 50% of the treated mice, per the CCNU dose which would result in the toxic death of 50% of the treated mice, without PB pretreatment was 2.1; the therapeutic index of CCNU after PB pretreatment was 1.7. There is no significant difference between the therapeutic indices. Thus, the reduction in the tumoricidal activity of CCNU after PB pretreatment was restored by increasing the dose of CCNU without a significant change in its lethal toxicity.l

Chemotherapy of an experimental glioma with nitrosoureas.

Chemotherapy experiments were performed with 2 nitro-sourea drugs in an experimental mouse brain tumor model. Cell suspensions of a transplantable mouse ependymoblastoma were injected i.c. by means of a stereotactic frame. The drugs used were 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea and 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea and were given by either i.p. or by direct intraneoplastic (i.n.) injection on the fifth day after tumor cell implantation. Injections i.n. of drugs were made with the stereotactic frame. Both drugs were highly effective in increasing the median day of death and in yielding large numbers of long-term survivors. Effectiveness was evident after i.p. or i.n. injection. However, with certain dosage schedules such as every 2 hr for 5 injections daily on 2 consecutive days, i.n. injection was more effective and less toxic than i.p. injection. The reason why repeated i.n. injections produced less toxicity than repeated i.p. injections is not definitely known but may be due to local metabolism of the drugs in the tumors and surrounding brain to a less toxic form. This is the first laboratory report of direct i.n. injection of the nitrosoureas, and the authors consider these results encouraging.

Frontotemporal correlates of impulsivity and machine learning in retired professional athletes with a history of multiple concussions.

The frontotemporal cortical network is associated with behaviours such as impulsivity and aggression. The health of the uncinate fasciculus (UF) that connects the orbitofrontal cortex (OFC) with the anterior temporal lobe (ATL) may be a crucial determinant of behavioural regulation. Behavioural changes can emerge after repeated concussion and thus we used MRI to examine the UF and connected gray matter as it relates to impulsivity and aggression in retired professional football players who had sustained multiple concussions. Behaviourally, athletes had faster reaction times and an increased error rate on a go/no-go task, and increased aggression and mania compared to controls. MRI revealed that the athletes had (1) cortical thinning of the ATL, (2) negative correlations of OFC thickness with aggression and task errors, indicative of impulsivity, (3) negative correlations of UF axial diffusivity with error rates and aggression, and (4) elevated resting-state functional connectivity between the ATL and OFC. Using machine learning, we found that UF diffusion imaging differentiates athletes from healthy controls with significant classifiers based on UF mean and radial diffusivity showing 79-84 % sensitivity and specificity, and 0.8 areas under the ROC curves. The spatial pattern of classifier weights revealed hot spots at the orbitofrontal and temporal ends of the UF. These data implicate the UF system in the pathological outcomes of repeated concussion as they relate to impulsive behaviour. Furthermore, a support vector machine has potential utility in the general assessment and diagnosis of brain abnormalities following concussion.

Injectable hydrogel promotes early survival of induced pluripotent stem cell-derived oligodendrocytes and attenuates longterm teratoma formation in a spinal cord injury model.

Transplantation of pluripotent stem cells and their differentiated progeny has the potential to preserve or regenerate functional pathways and improve function after central nervous system injury. However, their utility has been hampered by poor survival and the potential to form tumors. Peptide-modified biomaterials influence cell adhesion, survival and differentiation in vitro, but their effectiveness in vivo remains uncertain. We synthesized a peptide-modified, minimally invasive, injectable hydrogel comprised of hyaluronan and methylcellulose to enhance the survival and differentiation of human induced pluripotent stem cell-derived oligodendrocyte progenitor cells. Cells were transplanted subacutely after a moderate clip compression rat spinal cord injury. The hydrogel, modified with the RGD peptide and platelet-derived growth factor (PDGF-A), promoted early survival and integration of grafted cells. However, prolific teratoma formation was evident when cells were transplanted in media at longer survival times, indicating that either this cell line or the way in which it was cultured is unsuitable for human use. Interestingly, teratoma formation was attenuated when cells were transplanted in the hydrogel, where most cells differentiated to a glial phenotype. Thus, this hydrogel promoted cell survival and integration, and attenuated teratoma formation by promoting cell differentiation.

Left ventricular wall motion abnormalities in subarachnoid hemorrhage: an echocardiographic study.

Although electrocardiographic (ECG) abnormalities and autopsy evidence of myocardial necrosis are associated with subarachnoid hemorrhage, their relation to in vivo measures of left ventricular function in this condition has not been established. Thirteen patients with subarachnoid hemorrhage and no prior history of heart disease were studied by two-dimensional echocardiography, performed initially 10 to 48 h (mean 18) after admission and serially for less than or equal to 14 days. Serum creatine kinase (total and myocardial isoenzyme) was determined 5 times over the first 48 h; ECGs were performed daily. Neurologic state was assessed with the use of a standard grading system. Four patients (Group I) exhibited left ventricular wall motion abnormalities in one to eight segments. In two of these patients there was also left ventricular apical mural thrombus that embolized in one patient, leading to further neurologic deterioration. The initial creatine kinase myocardial isoenzyme was higher in Group I than in Group II (patients without wall motion abnormalities) (10.3 versus 2.1 U/liter, p less than 0.001), initial heart rate was higher (91 versus 61 beats/min, p less than 0.01), neurologic grade was higher (2.5 to 4.5 versus 1 to 2, p less than 0.001) and inverted T waves were more common (4 of 4 versus 1 of 9). Three of the four patients in Group I died; two of the three underwent autopsy and were found to have no significant coronary artery disease. No other patients died.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased intracranial pressure elicits hypertension, increased sympathetic activity, electrocardiographic abnormalities and myocardial damage in rats.

Intracranial pressure was increased in 59 rats by inflating a subdural balloon to a total mass volume of 0.3 ml. The increase in intracranial pressure ranged from 75 to greater than 500 mm Hg. With few exceptions, mean arterial pressure increased to as high as 227 mm Hg during the increase in intracranial pressure. Significant increases in plasma catecholamines, major electrocardiographic changes and a considerably shortened survival time were observed only in the rats that demonstrated an increase in mean arterial pressure greater than 50 mm Hg. A perfusion study with liquid silicone rubber (Microfil) revealed dilated irregular myocardial vessels with areas of focal constriction consistent with microvascular spasm. Histologic examination of the myocardium revealed widespread patches of contraction band necrosis and occasional contraction bands in the smooth muscle media of large coronary arteries. These observations suggest that myocardial damage after suddenly increased intracranial pressure resulted both from exposure to toxic levels of catecholamines and from myocardial reperfusion. Extension of these studies to humans suggests that a detailed assessment of myocardial function should be performed in victims of severe brain injury. Myocardial dysfunction may be a major determinant of the patient's prognosis or may render the heart unsuitable for transplantation.

Endogenous and exogenous CNS derived stem/progenitor cell approaches for neurotrauma.

Neural stem/progenitor cells capable of generating new neurons and glia, reside in specific areas of the adult mammalian central nervous system (CNS), including the ependymal region of the spinal cord and the subventricular zone (SVZ), hippocampus, and dentate gyrus of the brain. Much is known about the neurogenic regions in the CNS, and their response to various stimuli including injury, neurotrophins (NFs), morphogens, and environmental factors like learning, stress, and aging. This work has shaped our current views about the CNS's potential to recover lost tissue and function post-traumatically and the therapies to support the intrinsic regenerative capacity of the brain or spinal cord. Recently, intensive research has explored the potential of harvesting, culturing, and transplanting neural stem/progenitors as a therapeutic intervention for spinal cord injury (SCI) and traumatic brain injury (TBI). Another strategy has focused on maximizing the potential of this endogenous population of cells by stimulating their recruitment, proliferation, migration, and differentiation in vivo following traumatic lesions to the CNS. The promise of such experimental treatments has prompted tissue and biomaterial engineers to implant synthetic three-dimensional biodegradable scaffolds seeded with neural stem/progenitors into CNS lesions. Although there is no definitive answer about the ideal cell type for transplantation, strong evidence supports the use of region specific neural stem/progenitors. The technical and logistic considerations for transplanting neural stem/progenitors are extensive and crucial to optimizing and maintaining cell survival both before and after transplantation, as well as for tracking the fate of transplanted cells. These issues have been systematically addressed in many animal models, that has improved our understanding and approach to clinical therapeutic paradigms.

Proliferation, migration, and differentiation of endogenous ependymal region stem/progenitor cells following minimal spinal cord injury in the adult rat.

Ependymal cells of the adult mammalian spinal cord exhibit stem/progenitor cell properties following injury. In the present study, we utilized intraventricular injection of 1,1'-dioctadecyl-6,6'-di(4-sulfophenyl)-3,3,3',3'-tetramethylindocarbocyanine (DiI) to label the ependyma lining the central canal to allow tracking of the migration of endogenous ependymal cells and their progeny after spinal cord injury (SCI). We developed a minimal injury model that preserved the integrity of the central canal and did not interfere with ependymal cell labeling. Three days following SCI, there was an 8.6-fold increase in the proliferative labeling index of the ependymal cells at the level of the needle track based on bromodeoxyuridine labeling, compared with 1 day post-injury. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positive cells were not detected in the ependyma or surrounding gray matter, indicating that ependymal cells do not undergo apoptosis in response to minimal injury. Nestin was rapidly induced in the ependyma by 1 day and expression peaked by 7 days post-injury. We quantitated the number and distance of ependymal cell migration following minimal injury. The number of ependymal cells migrating from the region of the central canal increased by 3 days following minimal injury and DiI-labeled glial fibrillary acidic protein expressing cells were detected 14 days post-SCI, most of which migrated within 70 microm of the region of the central canal. These results show that a minimal SCI adjacent to the ependyma is sufficient to induce an endogenous ependymal cell response where ependymal stem/progenitor cells proliferate and migrate from the region of the central canal, differentiating primarily into astrocytes.

Epidermal growth factor and fibroblast growth factor 2 cause proliferation of ependymal precursor cells in the adult rat spinal cord in vivo.

We investigated the mitogenic effect of continuous intrathecal infusion of epidermal growth factor (EGF) or fibroblast growth factor 2 (FGF2) on ependymal precursor cells of the adult rat spinal cord in vivo. Either EGF, FGF2, EGF plus FGF2, or artificial cerebrospinal fluid (aCSF) was infused at a flow rate of 0.5 microl/h (15 ng/h of EGF or FGF2) for 3 or 14 days into the intrathecal space at T1 through a catheter attached to an osmotic minipump. To assess proliferation, the bromodeoxyuridine (BrdU) labeling index (LI) in the ependyma at T1 was calculated at 3 or 14 days. At 3 days there was no statistical difference in LI between these groups, but at 14 days the LI was significantly higher in the EGF plus FGF2 group (27.2% = 16.0%) than in the aCSF group (5.4% +/- 4.7%; p < 0.05). With EGF alone or FGF2 alone, the LI increases were not significantly different from the aCSF group. With EGF plus FGF2 for 14 days, some BrdU-positive cells in the ependyma also expressed nestin. These results suggest that the intrathecal infusion of EGF plus FGF2 has a mitogenic effect on precursor cells in the ependyma of the adult rat spinal cord.

Cell proliferation and nestin expression in the ependyma of the adult rat spinal cord after injury.

A population of precursor cells is known to exist in the subependyma of the lateral ventricles in adult rodents. However, the source of the precursor cells in the adult mammalian spinal cord has not been identified in vivo, although the adult spinal cord was recently reported to contain neural stem cells in vitro. In this study we found active cell proliferation and nestin expression in the adult ependyma of the central canal after spinal cord injury. The normal ependyma showed limited proliferative activity indicated by a low Ki-67 labeling index (1.5% at T1 level) and no immunoreactivity to nestin, a marker for neural precursor cells. In contrast, the spinal cord injured by clip compression demonstrated a dramatic increase in ependymal proliferation indicated by a high Ki-67 labeling index (maximum of 26% at 3 days [d] after injury) and concomitant strong nestin expression in the ependyma. These responses were downregulated by 7 d after injury. The increased cell proliferation in the ependyma was observed only at sites immediately adjacent to the lesion. After injury, nestin positive, GFAP negative cell populations were found in areas surrounding the ependymal layer, which suggests migration of the ependymal cells. These results indicate the precursor cell qualities of the adult ependyma after injury. Thus, we propose the ependyma of the central canal, which is normally latent but activates locally and temporally in response to spinal cord injury, as the in vivo source for precursor cells in the adult mammalian spinal cord.

Update on the pathophysiology and pathology of acute spinal cord injury.

There is evidence from both clinical and experimental studies that the spinal cord suffers both primary and secondary damage after acute spinal cord injury. The pathophysiology of secondary injury involves a multitude of cellular and molecular events which progress over the first few days after injury, the most important of which are systemic and local vascular insults, electrolyte shifts, oedema and excitotoxicity. These secondary processes contribute to the evolution of the pathological changes which in the severe injuries progress from central haemorrhagic necrosis involving mainly the grey matter to infarction of both the white and grey matter at the injury site and for a considerable distance proximally and distally. Less severe injuries show a variety of axonal and myelin changes. The concept of secondary injury is consistent with the results of therapeutic approaches to improve outcome.