Freeze-fracture studies of reactive myelinated nerve fibres after diffuse axonal injury

Traumatic Brain Injury in Alpine Winter Sports: Comparison of Two Case Series from a Swiss Trauma Center 30 Years Apart

BACKGROUND

 Between 3 and 15% of winter sports-related injuries are related to head injuries, which are the primary cause of mortality and disability among skiers. Despite the widespread adoption of helmets in winter sports, which has reduced the incidence of direct head injury, there is a paradoxical trend of an increasing number of individuals wearing helmets sustaining diffuse axonal injuries (DAI), which can result in severe neurologic sequelae.

METHODS

 We retrospectively reviewed 100 cases collected by the senior author of this work from 13 full winter seasons during the period from 1981 to 1993 and compared them with 17 patients admitted during the more shortened 2019 to 2020 ski season due to COVID-19. All data analyzed come from a single institution. Population characteristics, mechanism of injury, helmet use, need for surgical treatment, diagnosis, and outcome were collected. Descriptive statistics were used to compare the two databases.

RESULTS

 From February 1981 to January 2020, most skiers with head injuries were men (76% for the 1981-1993 and 85% for 2020). The proportion of patients aged over 50 increased from <20% in 1981 to 65% in 2020 (p < 0.01), with a median age of 60 years (range: 22-83 years). Low- to medium-velocity injuries were identified in 76% (13) of cases during the 2019 to 2020 season against 38% (28/74) during the 1981 to 1993 seasons (p < 0.01). All injured patients during the 2020 season wore a helmet, whereas none of the patients between 1981 and 1993 wore one (p < 0.01). DAI was observed in six cases (35%) for the 2019 to 2020 season against nine cases (9%) for the 1981 to 1993 season (p < 0.01). Thirty-four percent (34) of patients during the 1981 to 1993 seasons and 18% (3) of patients during the 2019 to 2020 season suffered skeletal fractures (p = 0.02). Among the 100 patients of the 1981 to 1993 seasons, 13 (13%) died against 1 (6%) from the recent season during care at the hospital (p = 0.15). Neurosurgical intervention was performed in 30 (30%) and 2 (12%) patients for the 1981 to 1993 and 2019 to 2020 seasons, respectively (p = 0.003). Neuropsychological sequelae were reported in 17% (7/42) of patients from the 1981 to 1993 seasons and cognitive evaluation before discharge detected significant impairments in 24% (4/17) of the patients from the 2019 to 2020 season (p = 0.29).

CONCLUSION

 Helmet use among skiers sustaining head trauma has increased from none in the period from 1981 to 1993 to 100% during the 2019 to 2020 season, resulting in a reduction in the number of skull fractures and deaths. However, our observations suggest a marked shift in the type of intracranial injuries sustained, including a rise in the number of skiers experiencing DAI, sometimes with severe neurologic outcomes. The reasons for this paradoxical trend can only be speculated upon, leading to the question of whether the perceived benefits of helmet use in winter sports are actually misinterpreted.

Epigenetic changes following traumatic brain injury and their implications for outcome, recovery and therapy

Traumatic brain injury (TBI) contributes to nearly a third of all injury-related deaths in the United States. For survivors of TBI, depending on severity, patients can be left with devastating neurological disabilities that include impaired cognition or memory, movement, sensation, or emotional function. Despite the efforts to identify novel therapeutics, the only strategy to combat TBI is risk reduction (helmets, seatbelts, removal of fall hazards, etc.). Enormous heterogeneity exists within TBI, and it depends on the severity, the location, and whether the injury was focal or diffuse. Evidence from recent studies support the involvement of epigenetic mechanisms such as DNA methylation, chromatin post-translational modification, and miRNA regulation of gene expression in the post-injured brain. In this review, we discuss studies that have assessed epigenetic changes and mechanisms following TBI, how epigenetic changes might not only be limited to the nucleus but also impact the mitochondria, and the implications of these changes with regard to TBI recovery.

Understanding secondary injury

Secondary injury is a term applied to the destructive and self-propagating biological changes in cells and tissues that lead to their dysfunction or death over hours to weeks after the initial insult (the "primary injury"). In most contexts, the initial injury is usually mechanical. The more destructive phase of secondary injury is, however, more responsible for cell death and functional deficits. This subject is described and reviewed differently in the literature. To biomedical researchers, systemic and tissue-level changes such as hemorrhage, edema, and ischemia usually define this subject. To cell and molecular biologists, "secondary injury" refers to a series of predominately molecular events and an increasingly restricted set of aberrant biochemical pathways and products. These biochemical and ionic changes are seen to lead to death of the initially compromised cells and "healthy" cells nearby through necrosis or apoptosis. This latter process is called "bystander damage." These viewpoints have largely dominated the recent literature, especially in studies of the central nervous system (CNS), often without attempts to place the molecular events in the context of progressive systemic and tissue-level changes. Here we provide a more comprehensive and inclusive discussion of this topic.

Quantitative relationship between axonal injury and mechanical response in a rodent head impact acceleration model

A modified Marmarou impact acceleration model was developed to study the mechanical responses induced by this model and their correlation to traumatic axonal injury (TAI). Traumatic brain injury (TBI) was induced in 31 anesthetized male Sprague-Dawley rats (392±13 g) by a custom-made 450-g impactor from heights of 1.25 m or 2.25 m. An accelerometer and angular rate sensor measured the linear and angular responses of the head, while the impact event was captured by a high-speed video camera. TAI distribution along the rostro-caudal direction, as well as across the left and right hemispheres, was determined using β-amyloid precursor protein (β-APP) immunocytochemistry, and detailed TAI injury maps were constructed for the entire corpus callosum. Peak linear acceleration 1.25 m and 2.25 m impacts were 666±165 g and 907±501 g, respectively. Peak angular velocities were 95±24 rad/sec and 124±48 rad/sec, respectively. Compared to the 2.25-m group, the observed TAI counts in the 1.25-m impact group were significantly lower. Average linear acceleration, peak angular velocity, average angular acceleration, and surface righting time were also significantly different between the two groups. A positive correlation was observed between normalized total TAI counts and average linear acceleration (R(2)=0.612, p<0.05), and time to surface right (R(2)=0.545, p<0.05). Our study suggested that a 2.25-m drop in the Marmarou model may not always result in a severe injury, and TAI level is related to the linear and angular acceleration response of the rat head during impact, not necessarily the drop height.

Voxel-based analysis of diffusion tensor imaging in mild traumatic brain injury in adolescents

BACKGROUND AND PURPOSE

DTI of normal-appearing WM as evaluated by conventional MR imaging in mTBI has the potential to identify important regional abnormalities that relate to PCS. VBA was used to examine WM changes in acute mTBI.

MATERIALS AND METHODS

WM was assessed between 1 and 6 days postinjury with voxel-based DTI analyses in 10 adolescent patients with mTBI and 10 age-matched control participants. In addition to the voxel-based group, analysis used to identify brain pathology across all patients with mTBI, 2 voxel-based linear regressions were performed. These analyses investigated the relation between 1) the ADC and PCS severity scores, and 2) ADC and scores on the BSI of emotional symptoms associated with mTBI. We hypothesized that frontotemporal WM changes would relate to symptoms associated with PCS and endorsed on the BSI.

RESULTS

Patients with mTBI demonstrated significant reductions in ADC in several WM regions and in the left thalamus. As expected, no increases in ADC were found in any region of interest. All injury-affected regions showed decreased radial diffusivity, unchanged AD, and increased FA, which is consistent with axonal cytotoxic edema, reflective of acute injury.

CONCLUSIONS

Whole-brain WM DTI measures can detect abnormalities in acute mTBI associated with PCS symptoms in adolescents.

The neurophysiology of brain injury

OBJECTIVE

This article reviews the mechanisms and pathophysiology of traumatic brain injury (TBI).

METHODS

Research on the pathophysiology of diffuse and focal TBI is reviewed with an emphasis on damage that occurs at the cellular level. The mechanisms of injury are discussed in detail including the factors and time course associated with mild to severe diffuse injury as well as the pathophysiology of focal injuries. Examples of electrophysiologic procedures consistent with recent theory and research evidence are presented.

RESULTS

Acceleration/deceleration (A/D) forces rarely cause shearing of nervous tissue, but instead, initiate a pathophysiologic process with a well defined temporal progression. The injury foci are considered to be diffuse trauma to white matter with damage occurring at the superficial layers of the brain, and extending inward as A/D forces increase. Focal injuries result in primary injuries to neurons and the surrounding cerebrovasculature, with secondary damage occurring due to ischemia and a cytotoxic cascade. A subset of electrophysiologic procedures consistent with current TBI research is briefly reviewed.

CONCLUSIONS

The pathophysiology of TBI occurs over time, in a pattern consistent with the physics of injury. The development of electrophysiologic procedures designed to detect specific patterns of change related to TBI may be of most use to the neurophysiologist.

SIGNIFICANCE

This article provides an up-to-date review of the mechanisms and pathophysiology of TBI and attempts to address misconceptions in the existing literature.

Post-acute alterations in the axonal cytoskeleton after traumatic axonal injury

All previous analyses of axonal responses to traumatic axonal injury (TAI) have described the ultrastructure of changes in the cytoskeleton and axolemma within 6 h of injury. In the present study we tested the hypothesis that there are, in addition, ultrastructural pathological changes up to 1 week after injury. TAI was induced in the adult guinea pig optic nerve of nine animals. Three animals were killed at either 4 h, 24 h, or 7 days (d) after injury. Quantitative analysis of the number or proportion of axons within 0.5-micro m-wide bins showed an increase in the number of axons with a diameter of less than 0.5 micro m at 4 h, 24 h, and 7 d, the presence of lucent axons at 24 h and 7 d and that the highest number of injured axons occurred about half way along the length of the nerve. A spectrum of pathological changes occurred in injured fibers-pathology of mitochondria; dissociation of myelin lamellae but little damage to the axon; loss of linear register of the axonal cytoskeleton; differential responses between microtubules (MT) and neurofilaments (NF) in different sizes of axon; two different sites of compaction of NF; loss of both NF (with an increase in their spacing) and MT (with a reduction in their spacing); replacement of the axoplasm by a flocculent precipitate; and an increased length of the nodal gap. These provide the first ultrastructural evidence for Wallerian degeneration of nerve fibers in an animal model of TAI.

Immunohistochemical indicators of early brain injury: an experimental study using the fluid-percussion model in cats

To detect early changes in neurons and astrocytes by immunohistochemical methods using antibodies against the neuron-specific enolase (NSE), neurofilament, glial fibrillary acid protein (GFAP), and S-100 protein, a fluid-percussion injury model in cats was chosen, in which a severe grade of injury (3.5-5.5 atm) was produced. Neuropathologic changes were produced through brain deformation by pressure gradients at the time of injury. The neuronal NSE immunoreactivity in the parietal cortex and the brain stem began to decrease at 1 to 2 hours after injury and were reduced markedly or even lost 4 hours after injury. Axons in the cerebral white matter and corpus callosum and in the hemorrhage regions at the brain stem were waved and enlarged <4 hours after injury. From 4 hours after injury, retraction balls were found after staining by antibody for the neurofilament. The GFAP-positive astrocytes appeared in the impact site in the parietal cortex and in the brain stem from 4 hours after injury, whereas S-100-positive astrocytes were not markedly changed, indicating that early after the injury, astrocytes manifested reactive hypertrophy without proliferation. These results suggest that immunochemical studies on NSE, neurofilament, GFAP, and S-100 are useful in pathologic and forensic practice in a patient who survives for a short time after a fatal head injury but without obvious focal damage.

Focal brain injury and its effects on cerebral mantle, neurons, and fiber tracks

Following a mild cortical impact injury delivered by a piston to the right sensorimotor cortex of the anesthetized rat, we evaluated mantle loss, neuronal changes, and fiber track degeneration by deOlmos silver stains up to 8 weeks after injury. Darkened neurons indicating damage (chromatolysis) occurred widely throughout both hemispheres and were seen from 1 h to 8 weeks after injury. This effect might have occurred from pressure wave damage from piston impact, brain displacement or deafferentation. Cerebral mantle loss was variable but fiber track degeneration related to projection and corticofugal descending tracks associated with the right sensorimotor system was rather constant. Unexpectedly, considerable fiber track degeneration occurred within the cerebellum, especially the inferior vermis. Cells directly under the piston face were surprisingly well-preserved but axon degeneration studies showed that these apparently intact neuronal cell bodies were surrounded by a dense network of degenerating fiber tracks. The intact cells, therefore, may have been functionally cut off from the rest of the brain owing to interruption of their efferents and afferents. The increased susceptibility of axons compared to cell bodies seen with this focal injury is similar to that observed with diffuse brain injury. The early appearing, severe and widespread axon damage we observed suggests that amelioration of focal traumatic brain injury will have to be directed promptly to the preservation of axons as well as cell bodies.

A mechanistic analysis of nondisruptive axonal injury: a review

Axons are particularly at risk in human diffuse head injury. Use of immunocytochemical labeling techniques has recently demonstrated that axonal injury (AI) and the ensuing reactive axonal change is, probably, more widespread and occurs over a longer posttraumatic time in the injured brain than had previously been appreciated. But the characterization of morphologic or reactive changes occurring after nondisruptive AI has largely been defined from animal models. The comparability of AI in animal models to human diffuse AI (DAI) is discussed and the conclusion drawn that, although animal models allow the analysis of morphologic changes, the spatial distribution within the brain and the time course of reactive axonal change differs to some extent both between species and with the mode of brain injury. Thus, the majority of animal models do not reproduce exactly the extent and time course of AI that occurs in human DAI. Nonetheless, these studies provide good insight into reactive axonal change. In addition, there is developing in the literature considerable variance in the terminology applied to injured axons or nerve fibers. We explain our current understanding of a number of terms now present in the literature and suggest the adoption of a common terminology. Recent work has provided a consensus that reactive axonal change is linked to pertubation of the axolemma resulting in disruption of ionic homeostatic mechanisms within injured nerve fibers. But quantitative data for changes for different ion species is lacking and is required before a better definition of this homeostatic disruption may be provided. Recent studies of responses by the axonal cytoskeleton after nondisruptive AI have demonstrated loss of axonal microtubules over a period up to 24 h after injury. The biochemical mechanisms resulting in loss of microtubules are, hypothetically, mediated both by posttraumatic influx of calcium and activation of calmodulin. This loss results in focal accumulation of membranous organelles in parts of the length of damaged axons where the axonal diameter is greater than normal to form axonal swellings. We distinguish, on morphologic grounds, between axonal swellings and axonal bulbs. There is also a growing consensus regarding responses by neurofilaments after nondisruptive AI. Initially, and rapidly after injury, there is reduced spacing or compaction of neurofilaments. This compaction is stable over at least 6 h and results from the loss or collapse of neurofilament sidearms but retention of the filamentous form of the neurofilaments. We posit that sidearm loss may be mediated either through proteolysis of sidearms via activation of microM calpain or sidearm dephosphorylation via posttraumatic, altered interaction between protein phosphatases and kinase(s), or a combination of these two, after calcium influx, which occurs, at least in part, as a result of changes in the structure and functional state of the axolemma. Evidence for proteolysis of neurofilaments has been obtained recently in the optic nerve stretch injury model and is correlated with disruption of the axolemma. But the earliest posttraumatic interval at which this was obtained was 4 h. Clearly, therefore, no evidence has been obtained to support the hypothesis that there is rapid, posttraumatic proteolysis of the whole axonal cytoskeleton mediated by calpains. Rather, we hypothesize that such proteolysis occurs only when intra-axonal calcium levels allow activation of mM calpain and suggest that such proteolysis, resulting in the loss of the filamentous structure of neurofilaments occurs either when the amount of deformation of the axolemma is so great at the time of injury to result in primary axotomy or, more commonly, is a terminal degenerative change that results in secondary axotomy or disconnection some hours after injury.

Cytochemical evidence for redistribution of membrane pump calcium-ATPase and ecto-Ca-ATPase activity, and calcium influx in myelinated nerve fibres of the optic nerve after stretch injury

There has been controversy for some time as to whether a posttraumatic influx of calcium ions occurs in stretch/nondisruptively injured axons within the central nervous system in both human diffuse axonal injury and a variety of models of such injury. We have used the oxalate/pyroantimonate technique to provide cytochemical evidence in support of such an ionic influx after focal axonal injury to normoxic guinea pig optic nerve axons, a model for human diffuse axonal injury. We present evidence for morphological changes within 15 min of injury where aggregates of pyroantimonate precipitate occur in nodal blebs at nodes of Ranvier, in focal swellings within axonal mitochondria, and at localized sites of separation of myelin lamellae. In parallel with these studies, we have used cytochemical techniques for localization of membrane pump Ca(2+)-ATPase and ecto-Ca-ATPase activity. There is loss of labelling for membrane pump Ca(2+)-ATPase activity on the nodal axolemma, together with loss of ecto-Ca-ATPase from the external aspect of the myelin sheath at sites of focal separation of myelin lamellae. Disruption of myelin lamellae and loss of ecto-Ca-ATPase activity becomes widespread between 1 and 4 h after injury. This is correlated with both infolding and retraction of the axolemma from the internal aspect of the myelin sheath to form periaxonal spaces which are characterized by aggregates of pyroantimonate precipitate, and the development of myelin intrusions into invaginations of the axolemma such that the regular profile of the axon is lost. There is novel labelling of membrane pump Ca(2+)-ATPase on the cytoplasmic aspect of the internodal axolemma between 1 and 4 h after injury. There is loss of an organized axonal cytoskeleton in a proportion of nerve fibres by 4-6 h after injury. We suggest that these changes demonstrate a progressive pathology linked to calcium ion influx after stretch (non-disruptive) axonal injury to optic nerve myelinated fibres. We posit that calcium influx, linked to or correlated with changes in Ca(2+)-ATPase activities, results in dissolution of the axonal cytoskeleton and axotomy between 4 and 6 h after the initial insult to axons.

The pathobiology of traumatically induced axonal injury in animals and humans: a review of current thoughts

This manuscript provides a review of those factors involved in the pathogenesis of traumatically induced axonal injury in both animals and man. The review comments on the issue of primary versus secondary, or delayed, axotomy, pointing to the fact that in cases of experimental traumatic brain injury, secondary, or delayed, axotomy predominates. This review links the process of secondary axotomy to an impairment of axoplasmic transport which is initiated, depending upon the severity of the injury, by either focal cytoskeletal. misalignment or axolemmal permeability change with concomitant cytoskeletal. collapse. Data are provided to show that these focal axonal changes are related to the focal impairment of axoplasmic transport which, in turn, triggers the progression of reactive axonal change, leading to disconnection. In the context of experimental studies, evidence is also provided to explain the damaging consequences of diffuse axonal injury. The implications of diffuse axonal injury and its attendant deafferentation are considered by noting that with mild injury such deafferentation may lead to an adaptive neuroplastic recovery, whereas in more severe injury a disordered and/or maladaptive neuroplastic re-organization occurs, consistent with the enduring morbidity associated with severe injury. In closing, the review focuses on the implications of the findings made in experimental animals for our understanding of those events ongoing in traumatically brain-injured humans. It is noted that the findings made in experimental animals have been confirmed, in large part, in humans, suggesting the relevance of animal models for continued study of human traumatically induced axonal injury.

A qualitative and quantitative analysis of the response of the retinal ganglion cell soma after stretch injury to the adult guinea-pig optic nerve

The development of a model for focal axonal injury in the optic nerve of the adult guinea-pig has allowed a qualitative and quantitative analysis of the response of the retinal ganglion cell soma to this type of injury. Large and medium sized retinal ganglion cells show classic 'central chromatolysis' in about 30% of ganglion cells between three and seven days after injury, a high proportion of which undergo degeneration between seven and 14 days. Small ganglion cells and small neurons do not demonstrate any morphological response to stretch injury of the optic nerve. However, a small number of larger ganglion cells demonstrate enlargement of the cell soma and nucleolus together with reconstitution of the rough endoplasmic reticulum between seven and 14 days after stretch injury. We suggest that these cells are either recovering from or regenerating after a non-disruptive lesion to their axons. We suggest that some of these morphological changes parallel documented regenerative responses in peripheral/extrinsic neurons after injury to their axons. We conclude that the time course of the 'axon reaction' after stretch injury to axons is longer than that obtained after crush or transection. We provide good morphological evidence that the level of injury after application of non-disruptive mechanical strain to axons is less severe than in the former two models of axonal injury and that a proportion of damaged neurons do not die but rather demonstrate either/or recovery or a regenerative response.

The pathological spectrum of diffuse axonal injury in blunt head trauma: assessment with axon and myelin strains

Although diffuse axonal injury (DAI) has been described as a major form of primary damage to the brain in blunt head injury, there has been no systematic study of the pathological changes in different regions of the brain. In this study, 22 cases of DAI were comprehensively examined histologically in the following areas: corpus callosum, internal capsule, superior cerebellar peduncles, cerebral white matter, fornix, rostral brain stem and globus pallidus, with a total of 17 standard blocks in each case. Sections were stained for axons with Glees and Marsland and neurofilament immunostaining and myelin with luxol fast blue and myelin basic protein immunostaining, and axonal retraction balls and myelin globoids were counted. Neurofilament immunostaining was superior to Glees and Marsland in both the positivity rates and the actual scores. Small myelin globoids were identified by the myelin stains, probably as a form of myelin damage secondary to axonal disruption. Such acute myelin damage was previously undescribed. There was no significant difference in both positivity rates and the scores obtained for luxol fast blue and myelin basic protein. Of all the regions of the brain examined, the internal capsule, corpus callosum and superior cerebellar peduncles yielded the highest counts of axonal balls as well as the highest incidences. It is recommended that in cases of DAI, these three regions of the brain should be examined most profitably with neurofilament immunostaining supplemented with a myelin stain.

Ultrastructural evidence of axonal shearing as a result of lateral acceleration of the head in non-human primates

The concept of shearing of axons at the time of non-impact injury to the head was first suggested in the middle of this century. However, no experimental model of diffuse axonal injury (DAI) has provided morphological confirmation of this concept. Evidence from experiments on invertebrate axons suggests that membrane resealing after axonal transection occurs between 5 and 30 min after injury. Thus, ultrastructural evidence in support of axonal shearing will probably only be obtained by examination of very short-term survival animal models. We have examined serial thin sections from the corpus callosum of non-human primates exposed to lateral acceleration of the head under conditions which induce DAI. Tearing or shearing of axons was obtained 20 and 35 min after injury, but not at 60 min. Axonal fragmentation occurred more frequently at the node/paranode but also in the internodal regions of axons. Fragmentation occurred most frequently in small axons. Axonal shearing was associated with dissolution of the cytoskeleton and the occurrence of individual, morphologically abnormal membranous organelles. There was no aggregation of membranous organelles at 20 and 35 min but small groups did occur in some axons at 60 minutes. We suggest that two different mechanisms of injury may be occurring in non-impact injury to the head. The first is shearing of axons and sealing of fragmented axonal membranes within 60 min. A second mechanism occurs in other fibres where perturbation of the axon results in axonal swelling and disconnection at a minimum of 2 h after injury.

Pathobiology of traumatically induced axonal injury in animals and man

STUDY OBJECTIVES

Although diffuse axonal injury is recognized as a consistent feature of traumatic brain injury, there is confusion regarding its pathogenesis. To provide insight into its pathogenesis, animal models of traumatic brain injury complemented by post mortem human analyses were used.

DESIGN

In animals, anterograde tracers together with antibodies targeting the neurofilament subunits were used in light and electron microscopic analyses of axonal injury. In humans, antibodies to the neurofilament subunits also were used to follow diffuse axonal injury. Animals were followed from minutes to months after injury, whereas humans were studied from six hours to 59 days after injury.

MEASUREMENTS AND MAIN RESULTS

In neither animals nor humans did traumatic brain injury cause direct axonal tearing. Instead, the traumatic brain injury triggered focal intra-axonal change in the 68-kd neurofilament subunit, which became disordered in its alignment and resulted in impaired axoplasmic transport. This caused axonal swelling and disconnection. The sequence of axonal change was similar in animals and man; however, its temporal progression was slower in humans.

CONCLUSION

Traumatically induced axonal damage is triggered first by focal intra-axonal change involving the neurofilament subunits. This neurofilament change is due to either direct mechanical failure of the axonal cytoskeleton or the initiation of a biochemical event that causes neurofilament disassembly. In general, the temporal progression of the intra-axonal changes that lead to ultimate disconnection is influenced by the severity of the traumatic injury and the species evaluated.

Pathological study of diffuse axonal injury patients who died shortly after impact

It is generally considered that axonal injury is apparent only on electron microscopy in the very early stage after a closed head injury. To clarify the pathological findings in head injury patients dying very shortly after the impact, we analyzed 8 fatal cases of diffuse axonal injury (DAI) who underwent medicolegal autopsy at the Department of Forensic Medicine of Kyoto Prefectural University of Medicine. Seven cases died within one hour after injury and another one case died 3 days after injury. We studied these cases macroscopically, microscopically, and electron microscopically. Macroscopically all cases showed the typical findings of diffuse axonal injury. Microscopical study of the cases who died within one hour revealed no characteristic findings of DAI such as appearance of retraction balls or microglia. On the other hand, in the case who died only 3 days after injury it showed the typical retraction balls. Electron microscopic study showed the remarkable destruction of cytoskeletal structure of axons in all cases. From our results, it is reasonable to speculate that DAI may be common among head injury patients who die very soon after the impact.

Diffuse axonal injury in non-missile head injury

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Diffuse axonal injury in head injury: definition, diagnosis and grading

Diffuse axonal injury is one of the most important types of brain damage that can occur as a result of non-missile head injury, and it may be very difficult to diagnose post mortem unless the pathologist knows precisely what he is looking for. Increasing experience with fatal non-missile head injury in man has allowed the identification of three grades of diffuse axonal injury. In grade 1 there is histological evidence of axonal injury in the white matter of the cerebral hemispheres, the corpus callosum, the brain stem and, less commonly, the cerebellum; in grade 2 there is also a focal lesion in the corpus callosum; and in grade 3 there is in addition a focal lesion in the dorsolateral quadrant or quadrants of the rostral brain stem. The focal lesions can often only be identified microscopically. Diffuse axonal injury was identified in 122 of a series of 434 fatal non-missile head injuries--10 grade 1, 29 grade 2 and 83 grade 3. In 24 of these cases the diagnosis could not have been made without microscopical examination, while in a further 31 microscopical examination was required to establish its severity.