Diffuse Axonal Injury in Head Trauma

Boomerang sign on MRI

INTRODUCTION

Altered mental status and more subtle cognitive and personality changes after traumatic brain injury (TBI) are pervasive problems in patients who survive initial injury. MRI is not necessarily part of the diagnostic evaluation of these patients.

METHODS

Case report with relevant image and review of the literature.

RESULTS

Injury to the corpus callosum is commonly described in traumatic brain injury; however, extensive lesions in the splenium are not well described. This image shows an important pattern of brain injury and demonstrates a common clinical syndrome seen in patients with corpus callosum pathology.

CONCLUSION

Injury to the splenium of the corpus callosum due to trauma may be extensive and can cause significant neurologic deficits. MRI is important in the diagnostic evaluation of patients with cognitive changes after TBI.

Neuron-specific enolase and S100BB as outcome predictors in severe diffuse axonal injury

BACKGROUND

Diffuse axonal injury (DAI) is a common type of traumatic brain injury, mostly associated with mild changes on computed tomography (CT) scan. Serum biomarkers might be used in the diagnosis and prognosis of this injury type. Our purpose was to determine temporal profile and predictive values of serum concentrations of protein S100BB and neuron-specific enolase (NSE) after DAI.

METHODS

Twenty-eight isolated severe DAI patients (Glasgow Coma Scale score ≤ 8) with normal CT were enrolled in the study. Serum levels of S100BB and NSE were determined at 6 hours, 24 hours, 48 hours, and 72 hours after injury, using enzyme-linked immunosorbent assay. Clinical outcome variables of DAI comprised survival at discharge and Glasgow Outcome scale (GOS) after 3 months and also 2 years.

RESULTS

S100BB concentration was maximum in 6 hours after injury (median = 280.75 ng/L) followed by a quick drop. Its value was significantly higher on third day in patients with unfavorable outcome (GOS score = 1-3) versus favorable outcome (GOS score = 4, 5) (p < 0.0001). The values of NSE had mild changes during 3 days; however, these measured values at 72 hours after trauma manifested higher in unfavorable outcome (p < 0.05).

CONCLUSIONS

Increased serum concentrations of NSE and S100BB within first 3 days after DAI are associated with poor outcome despite mild CT findings. S100BB level at 72 hours after injury can predict late outcome in DAI patients.

LEVEL OF EVIDENCE

Prognostic study, level III.

Lysosomal fusion dysfunction as a unifying hypothesis for Alzheimer's disease pathology

Alzheimer's disease is characterized pathologically by extracellular senile plaques, intracellular neurofibrillary tangles, and granulovacuolar degeneration. It has been debated whether these hallmark lesions are markers or mediators of disease progression, and numerous paradigms have been proposed to explain the appearance of each lesion individually. However, the unfaltering predictability of these lesions suggests a single pathological nidus central to disease onset and progression. One of the earliest pathologies observed in Alzheimer's disease is endocytic dysfunction. Here we review the recent literature of endocytic dysfunction with particular focus on disrupted lysosomal fusion and propose it as a unifying hypothesis for the three most-studied lesions of Alzheimer's disease.

The nuclear factor erythroid 2-like 2 activator, tert-butylhydroquinone, improves cognitive performance in mice after mild traumatic brain injury

Traumatic Brain injury affects at least 1.7 million people in the United States alone each year. The majority of injuries are categorized as mild but these still produce lasting symptoms that plague the patient and the medical field. Currently treatments are aimed at reducing a patient's symptoms, but there is no effective method to combat the source of the problem, neuronal loss. We tested a mild, closed head traumatic brain injury model for the effects of modulation of the antioxidant transcription factor Nrf2 by the chemical activator, tert-butylhydroquinone (tBHQ). We found that post-injury visual memory was improved by a 7 day course of treatment and that the level of activated caspase-3 in the hippocampus was reduced. The injury-induced memory loss was also reversed by a single injection at 30 min after injury. Since the protective stress response molecule, HSP70, can be upregulated by Nrf2, we examined protein levels in the hippocampus, and found that HSP70 was elevated by the injury and then further increased by the treatment. To test the possible role of HSP70, model neurons in culture exposed to a mild injury and treated with the Nrf2 activator displayed improved survival that was blocked by the HSP70 inhibitor, VER155008. Following mild traumatic brain injury, there may be a partial protective response and patients could benefit from directed enhancement of regulatory pathways such as Nrf2 for neuroprotection.

A robust method for investigating thalamic white matter tracts after traumatic brain injury

Damage to the structural connections of the thalamus is a frequent feature of traumatic brain injury (TBI) and can be a key factor in determining clinical outcome. Until recently it has been difficult to quantify the extent of this damage in vivo. Diffusion tensor imaging (DTI) provides a validated method to investigate traumatic axonal injury, and can be applied to quantify damage to thalamic connections. DTI can also be used to assess white matter tract structure using tractography, and this technique has been used to study thalamo-cortical connections in the healthy brain. However, the presence of white matter injury can cause failure of tractography algorithms. Here, we report a method for investigating thalamo-cortical connectivity that bypasses the need for individual tractography. We first created a template for a number of thalamo-cortical connections using probabilistic tractography performed in ten healthy subjects. This template for investigating white matter structure was validated by comparison with individual tractography in the same group, as well as in an independent control group (N = 11). We also evaluated two methods of masking tract location using the tract skeleton generated by tract based spatial statistics, and a cerebrospinal fluid mask. Voxel-wise estimates of fractional anisotropy derived from the template were more strongly correlated with individual tractography when both types of masking were used. The tract templates were then used to sample DTI measures from a group of TBI patients (N = 22), with direct comparison performed against probabilistic tractography in individual patients. Probabilistic tractography often failed to produce anatomically plausible tracts in TBI patients. Importantly, we show that this problem increases as tracts become more damaged, and leads to underestimation of the amount of traumatic axonal injury. In contrast, the tract template can be used in these cases, allowing a more accurate assessment of white matter damage. In summary, we propose a method suitable for assessing specific thalamo-cortical white matter connections after TBI that is robust to the presence of varying amounts of traumatic axonal injury, as well as highlighting the potential problems of applying tractography algorithms in patient populations.

SC1/hevin identifies early white matter injury after ischemia and intracerebral hemorrhage in young and aged rats

The progression of white matter damage after ischemic and hemorrhagic strokes can exacerbate the initial injury, but little is known about the processes involved. We show that the antiadhesive matricellular glycoprotein SC1 is a novel early marker of white matter damage in 3 models of acute injury in the rat striatum: transient focal ischemia, intracerebral hemorrhage, and a needle penetration wound. SC1 was restricted to the damaged portions of axon bundles that bordered stroke lesions in young-adult and aged rats. SC1 peaked at 1 and 3 days after intracerebral hemorrhage and at 7 days after ischemia. The SC1-positive bundles usually expressed degraded myelin basic protein and amyloid precursor protein, a marker of axonal injury. At the hematoma edge, SC1 was seen in a few axon bundles that retained myelin basic protein staining. In these bundles, punctate SC1 staining filled individual axons, extended beyond a core of pan-axonal neurofilament and NF200 and was inside or overlapped with myelin basic protein staining when it was present. Aged rats had less SC1 (and amyloid precursor protein) after both types of stroke, suggesting a reduced axonal response. SC1 also labeled amyloid precursor protein-positive axon bundles along the needle penetration tract of saline-injected rats; thus, SC1 appears to characterize damaged striatal white matter damage after multiple types of injury.

Administration of COG1410 reduces axonal amyloid precursor protein immunoreactivity and microglial activation after controlled cortical impact in mice

Traumatic axonal injury (TAI) accounts for at least 35% of the morbidity and mortality in traumatic brain injury (TBI) patients without space-occupying lesions. It is also believed to be a key determinant of adverse outcomes such as cognitive dysfunction across the spectrum of TBI severity. Previous studies have shown that COG1410, a synthetic peptide derived from the apolipoprotein E (apoE) receptor binding region, has anti-inflammatory effects after experimental TBI, with improvements in cognitive recovery. However, the effects of COG1410 on axonal injury following TBI are not known. The current study evaluated the effects of 1 mg/kg daily COG1410 versus saline administered intravenously starting 30 min after controlled cortical impact (CCI) injury on pericontusional TAI in young, wild-type C57BL6/J male mice. We found that COG1410 did not affect the number of amyloid precursor protein (APP)-immunoreactive axonal varicosities in the pericontusional corpus callosum and external capsule at 24 h, but reduced APP-immunoreactive varicosities by 31% at 3 days (p=0.0023), and 36% at 7 days (p=0.0009). COG1410 significantly reduced the number of Iba1-positive cells with activated microglial morphology at all three time points by 21-30%. There was no effect of COG1410 on pericontusional white matter volume or silver staining at any time point. This indicates a possible effect of COG1410 on delayed but not immediate TAI. Future studies are needed to investigate the underlying mechanisms, therapeutic time window, and physiological implications of this effect.

Transmission, attenuation and reflection of shear waves in the human brain

Traumatic brain injuries (TBIs) are caused by acceleration of the skull or exposure to explosive blast, but the processes by which mechanical loads lead to neurological injury remain poorly understood. We adapted motion-sensitive magnetic resonance imaging methods to measure the motion of the human brain in vivo as the skull was exposed to harmonic pressure excitation (45, 60 and 80 Hz). We analysed displacement fields to quantify the transmission, attenuation and reflection of distortional (shear) waves as well as viscoelastic material properties. Results suggest that internal membranes, such as the falx cerebri and the tentorium cerebelli, play a key role in reflecting and focusing shear waves within the brain. The skull acts as a low-pass filter over the range of frequencies studied. Transmissibility of pressure waves through the skull decreases and shear wave attenuation increases with increasing frequency. The skull and brain function mechanically as an integral structure that insulates internal anatomic features; these results are valuable for building and validating mathematical models of this complex and important structural system.

Guilty molecules, guilty minds? The conflicting roles of the innate immune response to traumatic brain injury

Traumatic brain injury (TBI) is a complex disease in the most complex organ of the body, whose victims endure lifelong debilitating physical, emotional, and psychosocial consequences. Despite advances in clinical care, there is no effective neuroprotective therapy for TBI, with almost every compound showing promise experimentally having disappointing results in the clinic. The complex and highly interrelated innate immune responses govern both the beneficial and deleterious molecular consequences of TBI and are present as an attractive therapeutic target. This paper discusses the positive, negative, and often conflicting roles of the innate immune response to TBI in both an experimental and clinical settings and highlights recent advances in the search for therapeutic candidates for the treatment of TBI.

Temporal assessment of traumatic axonal injury in the rat corpus callosum and optic chiasm

Impaired axoplasmic transport (IAT) and neurofilament compaction (NFC), two common axonal pathology processes involved in traumatic axonal injury (TAI), have been well characterized. TAI is found clinically and in animal models in brainstem white matter (WM) tracts and in the corpus callosum (CC), optic chiasm (Och), and internal capsule. Previous published quantitative studies of the time course of TAI expression induced by the Marmarou impact acceleration model have been limited to the brainstem. Accordingly, this study assessed the extent of IAT and NFC in the CC and Och at 8h, 28 h, 3 days and 7 days after traumatic brain injury (TBI) induction by the Marmarou impact acceleration model. IAT peak density was observed at 8h in the CC and 28 h in the Och post-TBI. NFC peak density was observed at 28 h in both structures. The density of IAT and NFC decreased with increasing survival time in both structures. The NFC density time profile followed a similar trend in both the Och and CC, whereas the IAT density time profile was variable between the Och and CC. Furthermore, a strong linear relationship was observed between IAT and NFC in the CC but not in the Och. These findings highlight the heterogeneity of TAI as evidenced by variable IAT and NFC injury time profiles in each anatomical structure. This variability indicates the requirement of multiple markers for a comprehensive TAI evaluation and multiple targeted treatments for TAI polypathology within its therapeutic window time frame.

Effect of nano-hydroxyapatite on the axonal guidance growth of rat cortical neurons

Nanomaterials such as carbon nanotubes (CNT) can improve axonal connecting in a target direction during regeneration, however, it is limited by the neurotoxicity of CNT. Here we investigate the possible protective effect of nano-hydroxyapatite (n-HA) against nerve injury, as well as CNT in cultured rat cortical neurons. In this study the nanomaterials were characterized by X-Ray diffractometry (XRD) and atomic force microscopy (AFM) analysis. Our results showed that axonal migration and extension were increased significantly after n-HA treatment by immunocytochemistry assay. The patch clamp assay results showed that n-HA acts protectively after nerve injury, which inhibited the average amplitude and frequency of excitatory postsynaptic currents (EPSCs). n-HA is not neurotoxic for the electrophysiology activity of cells. To find the effect of n-HA on axonal guidance growth in the cultured cortical neurons, Netrin 1, one of the axonal guidance cues, was determined by RT-PCR and western blot assay. Compared to the control group, n-HA down-regulated the mRNA level of netrin 1, and moreover, the expression of netrin 1 decreased significantly in the cells. n-HA caused the axonal guidance growth to be mediated by netrin 1 during nerve regeneration. Therefore, the data from the present study provided a new approach for the therapy or prevention of nerve injury.

Pathological and immunohistochemical study of lethal primary brain stem injuries

BACKGROUND

Many of the deaths that occur shortly after injury or in hospitals are caused by mild trauma. Slight morphological changes are often found in the brain stems of these patients during autopsy. The purpose of this study is to investigate the histopathological changes involved in primary brain stem injuries (PBSI) and their diagnostic significance.

METHODS

A total of 65 patients who had died of PBSI and other conditions were randomly selected. They were divided into 2 groups, an injury group (25 cases) and a control group (20 cases). Slides of each patient's midbrain, pons, and medulla oblongata were prepared and stained with HE, argentaffin, and immunohistochemical agents (GFAP, NF, amyloid-β, MBP). Under low power (×100) and NF staining, the diameter of the thickest longitudinal axon was measured at its widest point. Ten such diameters were collected for each part of the brain (midbrain, pons, and medulla oblongata). Data were recorded and analyzed statistically.

RESULTS

Brain stem contusions, astrocyte activity, edema, and pathological changes in the neurons were visibly different in the injury and control groups (P < 0.05). Characteristic changes occurred in the neural axons, axon diameter varied from axon to axon and even over different segments of one axon, and several pathological phenomena were observed. These included segmental thickening and curving, wave-like processing, disarrangement, and irregular swelling. A few axons ruptured and intumesced into retraction balls. Immunohistochemical MBP staining showed enlargement and curving of spaces between the myelin sheaths and axons in certain areas. The myelin sheaths lining the surfaces of the axons were in some cases incomplete and even exfoliated, and segmentation disappeared. These pathological changes increased in severity over time (P < 0.05).

CONCLUSIONS

These histopathological changes may prove beneficial to the pathological diagnosis of PBSI during autopsy. The measurement of axon diameters provides a referent quantitative index for the diagnosis of the specific causes of death involved in PBSI.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1345298818712204.

Temporal profiles of axonal injury following impact acceleration traumatic brain injury in rats--a comparative study with diffusion tensor imaging and morphological analysis

Traumatic axonal injury (TAI) plays a major role in the development of neurological impairments after traumatic brain injury (TBI), but it is commonly difficult to evaluate it precisely and early with conventional histological biomarkers, especially when the patients experience short-term survival after TBI. Diffusion tensor imaging (DTI) has shown some promise in detecting TAI, but longitudinal studies on the compromised white matter with DTI at early time points (≤72 h) following impact acceleration TBI are still absent. In the present study, rats were subjected to the Marmarou model and imaged with DTI at 3, 12, 24, and 72 h (n = 5 each) post-injury. Using a region-of-interest-based approach, the regions of interest including the corpus callosum, bilateral external capsule, internal capsule, and pyramidal tract were studied. Two DTI parameters, fraction anisotropy and axial diffusivity, were significantly reduced from 3 to 72 h in each region after trauma, corresponding to the gradient of axonal damage demonstrated by immunohistochemical staining of β-amyloid precursor protein and neurofilament light chain. Remarkably, DTI changes predicted the approximate time in the acute phase following TBI. These results indicate that the temporal profiles of diffusion parameters in DTI may be able to provide a tool for early diagnosis of TAI following impact acceleration TBI.

Coupled left-shift of Nav channels: modeling the Na⁺-loading and dysfunctional excitability of damaged axons

Injury to neural tissue renders voltage-gated Na⁺ (Nav) channels leaky. Even mild axonal trauma initiates Na⁺-loading, leading to secondary Ca²⁺-loading and white matter degeneration. The nodal isoform is Nav1.6 and for Nav1.6-expressing HEK-cells, traumatic whole cell stretch causes an immediate tetrodotoxin-sensitive Na⁺-leak. In stretch-damaged oocyte patches, Nav1.6 current undergoes damage-intensity dependent hyperpolarizing- (left-) shifts, but whether left-shift underlies injured-axon Nav-leak is uncertain. Nav1.6 inactivation (availability) is kinetically limited by (coupled to) Nav activation, yielding coupled left-shift (CLS) of the two processes: CLS should move the steady-state Nav1.6 "window conductance" closer to typical firing thresholds. Here we simulated excitability and ion homeostasis in free-running nodes of Ranvier to assess if hallmark injured-axon behaviors--Na⁺-loading, ectopic excitation, propagation block--would occur with Nav-CLS. Intact/traumatized axolemma ratios were varied, and for some simulations Na/K pumps were included, with varied in/outside volumes. We simulated saltatory propagation with one mid-axon node variously traumatized. While dissipating the [Na⁺] gradient and hyperactivating the Na/K pump, Nav-CLS generated neuropathic pain-like ectopic bursts. Depending on CLS magnitude, fraction of Nav channels affected, and pump intensity, tonic or burst firing or nodal inexcitability occurred, with [Na⁺] and [K⁺] fluctuating. Severe CLS-induced inexcitability did not preclude Na⁺-loading; in fact, the steady-state Na⁺-leaks elicited large pump currents. At a mid-axon node, mild CLS perturbed normal anterograde propagation, and severe CLS blocked saltatory propagation. These results suggest that in damaged excitable cells, Nav-CLS could initiate cellular deterioration with attendant hyper- or hypo-excitability. Healthy-cell versions of Nav-CLS, however, could contribute to physiological rhythmic firing.

Multi-scale mechanics of traumatic brain injury: predicting axonal strains from head loads

The length scales involved in the development of diffuse axonal injury typically range from the head level (i.e., mechanical loading) to the cellular level. The parts of the brain that are vulnerable to this type of injury are mainly the brainstem and the corpus callosum, which are regions with highly anisotropically oriented axons. Within these parts, discrete axonal injuries occur mainly where the axons have to deviate from their main course due to the presence of an inclusion. The aim of this study is to predict axonal strains as a result of a mechanical load at the macroscopic head level. For this, a multi-scale finite element approach is adopted, in which a macro-level head model and a micro-level critical volume element are coupled. The results show that the axonal strains cannot be trivially correlated to the tissue strain without taking into account the axonal orientations, which indicates that the heterogeneities at the cellular level play an important role in brain injury and reliable predictions thereof. In addition to the multi-scale approach, it is shown that a novel anisotropic equivalent strain measure can be used to assess these micro-scale effects from head-level simulations only.

Inhibition of JNK by a peptide inhibitor reduces traumatic brain injury-induced tauopathy in transgenic mice

Traumatic brain injury (TBI) is a major environmental risk factor for subsequent development of Alzheimer disease (AD). Pathological features that are common to AD and many tauopathies are neurofibrillary tangles (NFTs) and neuropil threads composed of hyperphosphorylated tau. Axonal accumulations of total and phospho-tau have been observed within hours to weeks, and intracytoplasmic NFTs have been documented years after severe TBI in humans. We previously reported that controlled cortical impact TBI accelerated tau pathology in young 3xTg-AD mice. Here, we used this TBI mouse model to investigate mechanisms responsible for increased tau phosphorylation and accumulation after brain trauma. We found that TBI resulted in abnormal axonal accumulation of several kinases that phosphorylate tau. Notably, c-Jun N-terminal kinase (JNK) was markedly activated in injured axons and colocalized with phospho-tau. We found that moderate reduction of JNK activity (40%) by a peptide inhibitor, D-JNKi1, was sufficient to reduce total and phospho-tau accumulations in axons of these mice with TBI. Longer-term studies will be required to determine whether reducing acute tau pathology proves beneficial in brain trauma.

Diffusion tensor imaging detects axonal injury in a mouse model of repetitive closed-skull traumatic brain injury

Mild traumatic brain injuries (TBI) are common in athletes, military personnel, and the elderly, and increasing evidence indicates that these injuries have long-term health effects. However, the difficulty in detecting these mild injuries in vivo is a significant impediment to understanding the underlying pathology and treating mild TBI. In the following experiments, we present the results of diffusion tensor imaging (DTI) and histological analysis of a model of mild repetitive closed-skull brain injury in mouse. Histological markers used included silver staining and amyloid precursor protein (APP) immunohistochemistry to detect axonal injury, and Iba-1 immunohistochemistry to assess microglial activation. At 24h post-injury, before silver staining or microglial abnormalities were apparent by histology, no significant changes in any of the DTI parameters were observed within white matter. At 7 days post-injury we observed a reduction in axial and mean diffusivity. Relative anisotropy at 7 days correlated strongly with the degree of silver staining. Interestingly, APP was not observed at any timepoint examined. In addition to the white matter alterations, mean diffusivity was elevated in ipsilateral cortex at 24h but returned to sham levels by 7 days. Altogether, this demonstrates that DTI is a sensitive method for detecting axonal injury despite a lack of conventional APP pathology. Further, this reflects a need to better understand the histological basis for DTI signal changes in mild TBI.

Tau elevations in the brain extracellular space correlate with reduced amyloid-β levels and predict adverse clinical outcomes after severe traumatic brain injury

Axonal injury is believed to be a major determinant of adverse outcomes following traumatic brain injury. However, it has been difficult to assess acutely the severity of axonal injury in human traumatic brain injury patients. We hypothesized that microdialysis-based measurements of the brain extracellular fluid levels of tau and neurofilament light chain, two low molecular weight axonal proteins, could be helpful in this regard. To test this hypothesis, 100 kDa cut-off microdialysis catheters were placed in 16 patients with severe traumatic brain injury at two neurological/neurosurgical intensive care units. Tau levels in the microdialysis samples were highest early and fell over time in all patients. Initial tau levels were >3-fold higher in patients with microdialysis catheters placed in pericontusional regions than in patients in whom catheters were placed in normal-appearing right frontal lobe tissue (P = 0.005). Tau levels and neurofilament light-chain levels were positively correlated (r = 0.6, P = 0.013). Neurofilament light-chain levels were also higher in patients with pericontusional catheters (P = 0.04). Interestingly, initial tau levels were inversely correlated with initial amyloid-β levels measured in the same samples (r = -0.87, P = 0.000023). This could be due to reduced synaptic activity in areas with substantial axonal injury, as amyloid-β release is closely coupled with synaptic activity. Importantly, high initial tau levels correlated with worse clinical outcomes, as assessed using the Glasgow Outcome Scale 6 months after injury (r = -0.6, P = 0.018). Taken together, our data add support for the hypothesis that axonal injury may be related to long-term impairments following traumatic brain injury. Microdialysis-based measurement of tau levels in the brain extracellular space may be a useful way to assess the severity of axonal injury acutely in the intensive care unit. Further studies with larger numbers of patients will be required to assess the reproducibility of these findings and to determine whether this approach provides added value when combined with clinical and radiological information.

Studying patients of severe traumatic brain injury with severe abdominal injury in Japan

Background:

Characteristics of extracranial injury in patients with diffuse axonal injury (DAI) have not been clarified.

Materials and Methods:

This retrospective study reviewed medical records from January 2003 to December 2007. Subjects comprised 35 patients meeting the following criteria: 1) head injury without mass lesion; 2) Glasgow coma scale (GCS) on arrival <15; and 3) magnetic resonance imaging (MRI) examination including T2*-weighted imaging. Subjects were divided into two groups: severe traumatic brain injury (TBI) group (patients with GCS ≤8, n=19) and moderate TBI group (patients with GCS >8, n=16).

Results:

Shock index (heart rate/systolic blood pressure) was significantly higher in the severe TBI group than in the moderate TBI group, while base excess on arrival was significantly lower in the severe TBI group than in the moderate TBI group. The abbreviated injury scale (AIS) for the face, thorax, extremities and external structures showed no significant differences between the severe TBI group, but AIS for the abdomen and the sum of extracranial AIS was greater in the severe TBI group than in the moderate TBI group. Duration of hospitalization was longer and outcomes were worse in the severe TBI group than in the moderate TBI group.

Conclusion:

Because patients with severe TBI are more likely to have abdominal injury than patients with moderate TBI, physicians should be aware of the potential for such complications when treating severe TBI.

Partial interruption of axonal transport due to microtubule breakage accounts for the formation of periodic varicosities after traumatic axonal injury

Due to their viscoelastic nature, white matter axons are susceptible to damage by high strain rates produced during traumatic brain injury (TBI). Indeed, diffuse axonal injury (DAI) is one of the most common features of TBI, characterized by the hallmark pathological profiles of axonal bulbs at disconnected terminal ends of axons and periodic swellings along axons, known as "varicosities." Although transport interruption underlies axonal bulb formation, it is unclear how varicosities arise, with multiple sites accumulating transported materials along one axon. Recently, axonal microtubules have been found to physically break during dynamic stretch injury of cortical axons in vitro. Here, the same in vitro model was used in parallel with histopathological analyses of human brains acquired acutely following TBI to examine the potential role of mechanical microtubule damage in varicosity formation post-trauma. Transmission electron microscopy (TEM) following in vitro stretch injury revealed periodic breaks of individual microtubules along axons that regionally corresponded with undulations in axon morphology. However, typically less than a third of microtubules were broken in any region of an axon. Within hours, these sites of microtubule breaks evolved into periodic swellings. This suggests axonal transport may be halted along one broken microtubule, yet can proceed through the same region via other intact microtubules. Similar axonal undulations and varicosities were observed following TBI in humans, suggesting primary microtubule failure may also be a feature of DAI. These data indicate a novel mechanism of mechanical microtubule damage leading to partial transport interruption and varicosity formation in traumatic axonal injury.

Engineering a high throughput axon injury system

Several key biological mechanisms of traumatic injury to axons have been elucidated using in vitro stretch injury models. These models, however, are based on the experimentation of single cultures keeping productivity slow. Indeed, low yield has hindered important and well-founded investigations requiring high throughput methods such as proteomic analyses. To meet this need, we engineered a multi-well high throughput injury device to accelerate and accommodate the next generation of traumatic brain injury research. This modular system stretch injures neuronal cultures in either a 24-well culture plate format or 6 individual wells simultaneously. Custom software control allows the user to accurately program the pressure pulse parameters to achieve the desired substrate deformation and injury parameters. Analysis of the pressure waveforms showed that peak pressure was linearly related to input pressure and valve open times and that the 6- and 24-well modules displayed rise times, peak pressures, and decays with extremely small standard deviations. Data also confirmed that the pressure pulse was distributed evenly throughout the pressure chambers and therefore to each injury well. Importantly, the relationship between substrate deformation and applied pressure was consistent among the multiple wells and displayed a predictable linear behavior in each module. These data confirm that this multi-well system performs as well as currently used stretch injury devices and can undertake high throughput studies that are needed across the field of neurotrauma research.

Animal modelling of traumatic brain injury in preclinical drug development: where do we go from here?

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. Survivors of TBI frequently suffer from long-term personality changes and deficits in cognitive and motor performance, urgently calling for novel pharmacological treatment options. To date, all clinical trials evaluating neuroprotective compounds have failed in demonstrating clinical efficacy in cohorts of severely injured TBI patients. The purpose of the present review is to describe the utility of animal models of TBI for preclinical evaluation of pharmacological compounds. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. To successfully develop compounds for clinical TBI, a thorough evaluation in several TBI models and injury severities is crucial. Additionally, brain pharmacokinetics and the time window must be carefully evaluated. Although the search for a single-compound, 'silver bullet' therapy is ongoing, a combination of drugs targeting various aspects of neuroprotection, neuroinflammation and regeneration may be needed. In summary, finding drugs and prove clinical efficacy in TBI is a major challenge ahead for the research community and the drug industry. For a successful translation of basic science knowledge to the clinic to occur we believe that a further refinement of animal models and functional outcome methods is important. In the clinical setting, improved patient classification, more homogenous patient cohorts in clinical trials, standardized treatment strategies, improved central nervous system drug delivery systems and monitoring of target drug levels and drug effects is warranted.

When basic research doesn't translate to the bedside--lessons from the magnesium brain trauma study

Magnesium Sulfate for Neuroprotection After Traumatic Brain Injury: A Randomised Controlled Trial. Temkin NR, Anderson GD, Winn HR, Ellenbogen RG, Britz GW, Schuster J, Lucas T, Newell DW, Mansfield PN, Machamer JE, Barber J, Dikmen SS. Lancet Neurol 2007;6(1):29–38. BACKGROUND: Traumatic brain injuries represent an important and costly health problem. Supplemental magnesium positively affects many of the processes involved in secondary injury after traumatic brain injury and consistently improves outcome in animal models. We aimed to test whether treatment with magnesium favourably affects outcome in head-injured patients. METHODS: In a double-blind trial, 499 patients aged 14 years or older admitted to a level 1 regional trauma centre between August, 1998, and October, 2004, with moderate or severe traumatic brain injury were randomly assigned one of two doses of magnesium or placebo within 8 h of injury and continuing for 5 days. Magnesium doses were targeted to achieve serum magnesium ranges of 1 0–1·85 mmol/L or 1·25–2·5 mmol/L. The primary outcome was a composite of mortality, seizures, functional measures, and neuropsychological tests assessed up to 6 months after injury. Analyses were done according to the intention-to-treat principle. This trial is registered with Clinicaltrials.gov, number NCT00004730. FINDINGS: Magnesium showed no significant positive effect on the composite primary outcome measure at the higher dose (mean = 55 average percentile ranking on magnesium vs. 52 on placebo, 95% CI for difference – 7 to 14; p = 0·70). Those randomly assigned magnesium at the lower dose did significantly worse than those assigned placebo (48 vs. 54, 95% CI −10·5 to −2; p = 0007). Furthermore, there was higher mortality with the higher magnesium dose than with placebo. Other major medical complications were similar between groups, except for a slight excess of pulmonary oedema and respiratory failure in the lower magnesium target group. No subgroups were identified in which magnesium had a significantly positive effect. INTERPRETATION: Continuous infusions of magnesium for 5 days given to patients within 8 h of moderate or severe traumatic brain injury were not neuroprotective and might even have a negative effect in the treatment of significant head injury.

Long-term cognitive and emotional consequences of mild traumatic brain injury

BACKGROUND

The objective of this study was to investigate long-term cognitive and emotional sequelae of mild traumatic brain injury (mTBI), as previous research has remained inconclusive with respect to their prevalence and extent.

METHOD

Thirty-three individuals who had sustained mTBI on average 6 years prior to the study and 33 healthy control subjects were matched according to age, gender and education. Structural brain damage at time of testing was excluded by magnetic resonance imaging (MRI). A comprehensive neuropsychological test battery was conducted to assess learning, recall, working memory, attention and executive function. Psychiatric symptoms were assessed by the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I) and the Beck Depression Inventory (BDI). Possible negative response bias was ruled out by implementing the Word Memory Test (WMT).

RESULTS

The mTBI individuals had significant impairments in all cognitive domains compared to the healthy control subjects. Effect sizes of cognitive deficits were medium to large, and could not be accounted for by self-perceived deficits, depression, compensation claims or negative response bias. BDI scores were significantly higher in the patient group, and three patients fulfilled DSM-IV criteria for a mild episode of major depression.

CONCLUSIONS

Primarily, well-recovered individuals who had sustained a minor trauma more than half a decade ago continue to have long-term cognitive and emotional sequelae relevant for everyday social and professional life. mTBI may lead to a lasting disruption of neurofunctional circuits not detectable by standard structural MRI and needs to be taken seriously in clinical and forensic evaluations.

Diffuse traumatic axonal injury in the mouse induces atrophy, c-Jun activation, and axonal outgrowth in the axotomized neuronal population

Traumatic axonal injury (TAI) is a consistent component of traumatic brain injury (TBI) and is associated with much of its morbidity. Little is known regarding the long-term retrograde neuronal consequences of TAI and/or the potential that TAI could lead to anterograde axonal reorganization and repair. To investigate the repertoire of anterograde and retrograde responses triggered by TIA, Thy1-YFP-H mice were subjected to mild central fluid percussion injury and killed at various times between 15 min and 28 d post-injury. Based upon confocal assessment of the endogenous neuronal fluorescence, such injury was found to result in diffuse TAI throughout layer V of the neocortex within yellow fluorescent protein (YFP)-positive axons. When these fluorescent approaches were coupled with various quantitative and immunohistochemical approaches, we found that this TAI did not result in neuronal death over the 28 d period assessed. Rather, it elicited neuronal atrophy. Within these same axotomized neuronal populations, TAI was also found to induce an early and sustained activation of the transcription factors c-Jun and ATF-3 (activating transcription factor 3), known regulators of axon regeneration. Parallel ultrastructural studies confirmed that these reactive changes are consistent with atrophy in the absence of neuronal death. Concurrent with those events ongoing in the neuronal cell bodies, their downstream axonal segments revealed, as early as 1 d post-injury, morphological changes consistent with reactive sprouting that was accompanied by significant axonal elongation over time. Collectively, these TAI-linked events are consistent with sustained neuronal recovery, an activation of a regenerative genetic program, and subsequent axonal reorganization suggestive of some form of regenerative response.

Non-impact, blast-induced mild TBI and PTSD: concepts and caveats

PRIMARY OBJECTIVE

A volumetric blood surge (rapid physical movement/displacement of blood) is hypothesized to cause the non-impact, mild TBI and battlefield PTSD induced by a blast over-pressure wave.

RESEARCH DESIGN

Systematic review of the literature.

METHODS AND PROCEDURES

Articles relating to the fields of blast injury, brain injury and relevant disorders were searched between the years 1968-2010 for keywords such as 'brain injury', 'post-traumatic stress disorder' and 'blast pressure wave'. Articles found through journal and Internet databases were cross-referenced.

MAIN OUTCOMES AND RESULTS

The blood surge, which is driven by elevated overall pressure in the ventral body cavity after exposure of the torso to blast wave, may move through blood vessels to the low-pressure cranial cavity from the high-pressure ventral body cavity. It dramatically increases cerebral perfusion pressure and causes damage to both tiny cerebral blood vessels and the BBB.

CONCLUSIONS

Three factors may be critical to the induction of blast-induced brain injuries: (1) the difference in pressure between the ventral body cavity and cranial cavity; (2) blood that acts as a transmission medium to propagate a pressure wave to the brain; and (3) the vulnerability of cerebral blood vessels and the BBB to a sudden fluctuation in perfusion pressure.

Traumatic brain injury: review of current management strategies

Head injury is a common condition with a high morbidity and mortality. Serious intracranial haematomas require early recognition and evacuation to maximise chances of independent outcomes. Recent organisational changes have promoted the development of trauma units and major trauma centres where patients can go through triage and be managed in an appropriate environment, and the development of management pathways in intensive treatment units has resulted in improvements in the outcome of traumatic brain injuries. Evidence for the treatment of cerebral perfusion pressure, and management of hyperventilation, osmotherapy, tracheostomy, and leakage of cerebrospinal fluid (CSF) has accumulated during the last decade and is important in the management of patients in all clinical settings. Since head injury is commonly associated with maxillofacial injuries, this review will be relevant to all who deal with this aspect of trauma.

Measurement of synchronous activity by microelectrode arrays uncovers differential effects of sublethal and lethal glutamate concentrations on cortical neurons

We grew cultures of rat cortical cells on microelectrode arrays to investigate the effects of glutamate-mediated neurotoxicity as a model of traumatic brain injury. Treatment with two different concentrations of glutamate, 175 and 250 μM, led to different outcomes. Cultures treated with 250 μM glutamate suffered a loss in overall activity that was not seen in cultures treated with 175 μM glutamate. An analysis of the changes in the synchronization of action potential firing between electrodes, however, revealed a loss of synchronization in subsets of electrode pairs treated with both the higher and lower concentrations of glutamate. We found that this loss of action potential synchronization was dependent on the initial amount of synchronization prior to injury. Finally, our data suggest that the synchronization of electrical activity as well as the susceptibility to loss of firing synchrony is independent of the distance between neurons in a network.

Cyclosporin A preserves mitochondrial function after traumatic brain injury in the immature rat and piglet

Cyclosporin A (CsA) has been shown to be neuroprotective in mature animal models of traumatic brain injury (TBI), but its effects on immature animal models of TBI are unknown. In mature animal models, CsA inhibits the opening of the mitochondrial permeability transition pore (MPTP), thereby maintaining mitochondrial homeostasis following injury by inhibiting calcium influx and preserving mitochondrial membrane potential. The aim of the present study was to evaluate CsA's ability to preserve mitochondrial bioenergetic function following TBI (as measured by mitochondrial respiration and cerebral microdialysis), in two immature models (focal and diffuse), and in two different species (rat and piglet). Three groups were studied: injured+CsA, injured+saline vehicle, and uninjured shams. In addition, we evaluated CsA's effects on cerebral hemodynamics as measured by a novel thermal diffusion probe. The results demonstrate that post-injury administration of CsA ameliorates mitochondrial dysfunction, preserves cerebral blood flow (CBF), and limits neuropathology in immature animals 24 h post-TBI. Mitochondria were isolated 24 h after controlled cortical impact (CCI) in rats and rapid non-impact rotational injury (RNR) in piglets, and CsA ameliorated cerebral bioenergetic crisis with preservation of the respiratory control ratio (RCR) to sham levels. Results were more dramatic in RNR piglets than in CCI rats. In piglets, CsA also preserved lactate pyruvate ratios (LPR), as measured by cerebral microdialysis and CBF at sham levels 24 h after injury, in contrast to the significant alterations seen in injured piglets compared to shams (p<0.01). The administration of CsA to piglets following RNR promoted a 42% decrease in injured brain volume (p<0.01). We conclude that CsA exhibits significant neuroprotective activity in immature models of focal and diffuse TBI, and has exciting translational potential as a therapeutic agent for neuroprotection in children.

Clinical characteristics and pathophysiological mechanisms of focal and diffuse traumatic brain injury

Traumatic brain injury (TBI) is a frequent and clinically highly heterogeneous neurological disorder with large socioeconomic consequences. TBI severity classification, based on the hospital admission Glasgow Coma Scale (GCS) score, ranges from mild (GCS 13-15) and moderate (GCS 9-12) to severe (GCS ≤ 8). The GCS reflects the risk of dying from TBI, which is low after mild (∼1%), intermediate after moderate (up to 15%) and high (up to 40%) after severe TBI. Intracranial damage can be focal, such as epidural and subdural haematomas and parenchymal contusions, or diffuse, for example traumatic axonal injury and diffuse cerebral oedema, although this distinction is somewhat arbitrary. Study of the cellular and molecular post-traumatic processes is essential for the understanding of TBI pathophysiology but even more to find therapeutic targets for the development of neuroprotective drugs to be eventually used in human beings. To date, studies in vitro and in vivo, mainly in animals but also in human beings, are unravelling the pathological TBI mechanisms at high pace. Nevertheless, TBI pathophysiology is all but completely elucidated. Neuroprotective treatment studies in human beings have been disappointing thus far and have not resulted in commonly accepted drugs. This review presents an overview on the clinical aspects and the pathophysiology of focal and diffuse TBI, and it highlights several acknowledged important events that occur on molecular and cellular level after TBI.

Biomarkers associated with diffuse traumatic axonal injury: exploring pathogenesis, early diagnosis, and prognosis

BACKGROUND

Diffuse traumatic axonal injury (dTAI) is a significant pathologic feature of traumatic brain injury and is associated with substantial mortality and morbidity. It is still a challenge for clinicians to make an early diagnosis of dTAI and generate accurate prognosis and direct therapeutic decisions because most patients rapidly progress to coma after trauma and because specific neurologic symptoms and focal lesions detectable with current routine imaging techniques are absent. To address these issues, many investigations have sought to identify biomarkers of dTAI.

METHODS

This article is a review of the pertinent medical literature.

RESULTS

From the perspective of the pathophysiology of dTAI, we reviewed several biomarkers that are associated with structural damage and biochemical cascades in the secondary injury or repair response to traumatic brain injury. Although some biomarkers are not specific to dTAI, they are nevertheless useful in elucidating its pathogenesis, making early diagnosis possible, predicting outcomes, and providing candidate targets for novel therapeutic strategies.

CONCLUSIONS

The availability of biomarker data, clinical case histories, and radiologic information can improve our current ability to diagnose and monitor pathogenic conditions and predict outcomes in patients with dTAI.

Glial cell-mediated deterioration and repair of the nervous system after traumatic brain injury in a rat model as assessed by positron emission tomography

Traumatic brain injury (TBI) is one of the most acute degenerative pathologies in the central nervous system, and in vivo indices enabling an assessment of TBI on a mechanistic basis have yet to be established. The aim of this work was to pursue neuroinflammatory changes and their link to functional disruptions of traumatically-damaged neurons in a rat model of TBI by longitudinal positron emission tomographic (PET) assays. TBI was induced in the unilateral frontal cortex of craniotomied rats according to a lateral fluid percussion brain injury protocol. The use of [(18)F]fluoroethyl-DAA1106 as a PET tracer for translocator protein (TSPO) permitted demonstration of the inflammatory response to the injury, peaking at 1 week after impact. This alteration was parallel to metabolic deficits assessed by PET with [(18)F]fluorodeoxyglucose, but the difference in TSPO levels between impacted and non-impacted frontal cortices was more than threefold of the interlateral metabolic difference, indicating superiority of TSPO imaging for sensitive detection of post-traumatic pathologies. Comparative PET, autoradiographic. and immunohistochemical investigations illustrated the primary contribution of hypertrophic microglia and macrophages to acute TSPO signals in the vicinity of the impact. Astrocytes also formed a TSPO-positive glial scar encompassing necrotic inflammation, and were clustered with PET-detectable TSPO signals in the bilateral external and internal capsules at late stages, putatively reacting with diffuse axonal injury. These observations support the applicability of TSPO-PET as an imaging-based preclinical and clinical biomarker assay in TBI, and indicate its potential capability to clarify aggressive and protective roles of glial responses to injury when combined with emerging anti-inflammatory and immunomodulatory treatments.

Assessing spatial relationships between axonal integrity, regional brain volumes, and neuropsychological outcomes after traumatic axonal injury

Diffuse traumatic axonal injury (TAI) is a type of traumatic brain injury (TBI) characterized predominantly by white matter damage. While TAI is associated with cerebral atrophy, the relationship between gray matter volumes and TAI of afferent or efferent axonal pathways remains unknown. Moreover, it is unclear if deficits in cognition are associated with post-traumatic brain volumes in particular regions. The goal of this study was to determine the relationship between markers of TAI and volumes of cortical and subcortical structures, while also assessing the relationship between cognitive outcomes and regional brain volumes. High-resolution magnetic resonance imaging scans were performed in 24 patients with TAI within 1 week of injury and were repeated 8 months later. Diffusion tensor imaging (DTI) tractography was used to reconstruct prominent white matter tracts and calculate their fractional anisotropy (FA) and mean diffusivity (MD) values. Regional brain volumes were computed using semi-automated morphometric analysis. Pearson's correlation coefficients were used to assess associations between brain volumes, white matter integrity (i.e., FA and MD), and neuropsychological outcomes. Post-traumatic volumes of many gray matter structures were associated with chronic damage to related white matter tracts, and less strongly associated with measures of white matter integrity in the acute scans. For example, left and right hippocampal volumes correlated with FA in the fornix body (r = 0.600, p = 0.001; r = 0.714, p < 0.001, respectively). In addition, regional brain volumes were associated with deficits in corresponding neuropsychological domains. Our results suggest that TAI may be a primary mechanism of post-traumatic atrophy, and provide support for regional morphometry as a biomarker for cognitive outcome after injury.

A unified science of concussion

The etiology, imaging, and behavioral assessment of mild traumatic brain injury (mTBI) are daunting fields, given the lack of a cohesive neurobiological explanation for the observed cognitive deficits seen following mTBI. Although subjective patient self-report is the leading method of diagnosing mTBI, current scientific evidence suggests that quantitative measures of predictive timing, such as visual tracking, could be a useful adjunct to guide the assessment of attention and to screen for advanced brain imaging. Magnetic resonance diffusion tensor imaging (DTI) has demonstrated that mTBI is associated with widespread microstructural changes that include those in the frontal white matter tracts. Deficits observed during predictive visual tracking correlate with DTI findings that show lesions localized in neural pathways subserving the cognitive functions often disrupted in mTBI. Unifying the anatomical and behavioral approaches, the emerging evidence supports an explanation for mTBI that the observed cognitive impairments are a result of predictive timing deficits caused by shearing injuries in the frontal white matter tracts.

Longitudinal changes in the corpus callosum following pediatric traumatic brain injury

BACKGROUND

Atrophy of the corpus callosum (CC) is a documented consequence of moderate-to-severe traumatic brain injury (TBI), which has been expressed as volume loss using quantitative magnetic resonance imaging (MRI). Other advanced imaging modalities such as diffusion tensor imaging (DTI) have also detected white matter microstructural alteration following TBI in the CC. The manner and degree to which macrostructural changes such as volume and microstructural changes develop over time following pediatric TBI, and their relation to a measure of processing speed is the focus of this longitudinal investigation. As such, DTI and volumetric changes in the CC in participants with TBI and a comparison group at approximately 3 and 18 months after injury as well as their relation to processing speed were determined.

METHODS

Forty-eight children and adolescents aged 7-17 years who sustained either complicated mild or moderate-to-severe TBI (n = 23) or orthopedic injury (OI; n = 25) were studied. The participants underwent brain MRI and were administered the Eriksen flanker task at both time points.

RESULTS

At 3 months after injury, there were significant group differences in DTI metrics in the total CC and its subregions (genu/anterior, body/central and splenium/posterior), with the TBI group demonstrating significantly lower fractional anisotropy (FA) and a higher apparent diffusion coefficient (ADC) in comparison to the OI group. These group differences were also present at 18 months after injury in all CC subregions, with lower FA and a higher ADC in the TBI group. In terms of longitudinal changes in DTI, despite the group difference in mean FA, both groups generally demonstrated a modest increase in FA over time though this increase was only significant in the splenium/posterior subregion. Interestingly, the TBI group also generally demonstrated ADC increases from 3 to 18 months though the OI group demonstrated ADC decreases over time. Volumetrically, the group differences at 3 months were marginal for the midanterior and body/central subregions and total CC. However, by 18 months, the TBI group demonstrated a significantly decreased volume in all subregions except the splenium/posterior area relative to the OI group. Unlike the OI group, which showed a significant volume increase in subregions of the CC over time, the TBI group demonstrated a significant and consistent volume decrease. Performance on a measure of processing speed did not differentiate the groups at either visit, and only the OI group showed significantly improved performance over time. Processing speed was related to FA in the splenium/posterior and total CC only in the TBI group on both occasions, with a stronger relation at 18 months.

CONCLUSION

In response to TBI, macrostructural volume loss in the CC occurred over time; yet, at the microstructural level, DTI demonstrated both indicators of continued maturation and development even in the damaged CC, as well as evidence of potential degenerative change. Unlike volumetrics, which likely reflects the degree of overall neuronal loss and axonal damage, DTI may reflect some aspects of postinjury maturation and adaptation in white matter following TBI. Multimodality imaging studies may be important to further understand the long-term consequences of pediatric TBI.

Visual tracking synchronization as a metric for concussion screening

Our goal was to determine whether performance variability during predictive visual tracking can provide a screening measure for mild traumatic brain injury (mTBI). Seventeen subjects with chronic postconcussive syndrome and 9 healthy control subjects were included in this study. Eye movements were recorded with video-oculography as the subject visually tracked a target that moved through a circular trajectory. We compared the variability of gaze positional errors relative to the target with the microstructural integrity of white matter tracts as measured by the fractional anisotropy (FA) parameter of diffusion tensor imaging. Gaze error variability was significantly correlated with the mean FA values of the right anterior corona radiata (ACR) and the left superior cerebellar peduncle, tracts that support spatial processing and sustenance of attention, and the genu of the corpus callosum. Because the ACR and the genu are among the most frequently damaged white matter tracts in mTBI, the correlations imply that gaze error variability during visual tracking may provide a useful screening tool for mTBI. Gaze error variability was also significantly correlated with attention and working memory measures in neurocognitive testing; thus, measurement of visual tracking performance is promising as a fast and practical screening tool for mTBI.

Prevalence and impact of diffuse axonal injury in patients with moderate and severe head injury: a cohort study of early magnetic resonance imaging findings and 1-year outcome

OBJECT

In this prospective cohort study the authors examined patients with moderate to severe head injuries using MR imaging in the early phase. The objective was to explore the occurrence of diffuse axonal injury (DAI) and determine whether DAI was related to level of consciousness and patient outcome.

METHODS

One hundred and fifty-nine patients (age range 5-65 years) with traumatic brain injury, who survived the acute phase, and who had a Glasgow Coma Scale (GCS) score of 3-13 were admitted between October 2004 and August 2008. Of these 159 patients, 106 were examined using MR imaging within 4 weeks postinjury. Patients were classified into 1 of 3 stages of DAI: Stage 1, in which lesions were confined to the lobar white matter; Stage 2, in which there were callosal lesions; and Stage 3, in which lesions occurred in the dorsolateral brainstem. The outcome measure used 12 months postinjury was the Glasgow Outcome Scale-Extended (GOSE).

RESULTS

Diffuse axonal injury was detected in 72% of the patients and a combination of DAI and contusions or hematomas was found in 50%. The GCS score was significantly lower in patients with "pure DAI" (median GCS Score 9) than in patients without DAI (median GCS Score 12; p < 0.001). The GCS score was related to outcome only in those patients with DAI (r = 0.47; p = 0.001). Patients with DAI had a median GOSE score of 7, and patients without DAI had a median GOSE score of 8 (p = 0.10). Outcome was better in patients with DAI Stage 1 (median GOSE Score 8) and DAI Stage 2 (median GOSE Score 7.5) than in patients with DAI Stage 3 (median GOSE Score 4; p < 0.001). Thus, in patients without any brainstem injury, there was no difference in good recovery between patients with DAI (67%) and patients without DAI (66%).

CONCLUSIONS

Diffuse axonal injury was found in almost three-quarters of the patients with moderate and severe head injury who survived the acute phase. Diffuse axonal injury influenced the level of consciousness, and only in patients with DAI was GCS score related to outcome. Finally, DAI was a negative prognostic sign only when located in the brainstem.