D. I. Graham

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.

Beta amyloid protein deposition in the brain after severe head injury: implications for the pathogenesis of Alzheimer's disease.

In a recent preliminary study it was reported that a severe head injury resulted in the deposition of beta amyloid protein (beta AP) in the cortical ribbon of 30% of patients who survived for less than two weeks. Multiple cortical areas have now been examined from 152 patients (age range 8 weeks-81 years) after a severe head injury with a survival time of between four hours and 2.5 years. This series was compared with a group of 44 neurologically normal controls (age range 51 to 80 years). Immunostaining with an antibody to beta AP confirmed the original findings that 30% of cases of head injury have beta AP deposits in one or more cortical areas. Increasing age seemed to accentuate the extent of beta AP deposition and potential correlations with other pathological changes associated with head injury were also investigated. In addition, beta amyloid precursor protein (beta APP) immunoreactivity was increased in the perikarya of neurons in the vicinity of beta AP deposits. The data from this study support proposals that increased expression of beta APP is part of an acute phase response to neuronal injury in the human brain, that extensive overexpression of beta APP can lead to deposition of beta AP and the initiation of an Alzheimer disease-type process within days, and that head injury may be an important aetiological factor in Alzheimers disease.

Ischaemic brain damage is still common in fatal non-missile head injury.

A detailed neuropathological examination has been undertaken on a consecutive series of head injuries dying in the Institute of Neurological Sciences, Glasgow, between 1968-72 (151 cases) and 1981-82 (112 cases) in order to determine the frequency and distribution of any ischaemic brain damage. Ischaemic damage was found in the brains of 92% of the 1968-72 cases and in 88% of the 1981-82 cases: there was no statistical difference in the amount of moderately severe and severe ischaemic damage in the two groups, 55% and 54% respectively. There was evidence, however, that an increased number of patients with severe ischaemic brain damage was admitted in 1981-82 as a result of a changed admission policy of the Department of Neurosurgery that resulted in an increased detection of intracranial haematomas. It is concluded that ischaemic brain damage is still common after severe head injury, and it seems likely that it remains an important cause of mortality and morbidity.

Quantitative assessment of early brain damage in a rat model of focal cerebral ischaemia.

A method for the volumetric assessment of early cerebral infarction, together with its statistical and biological validation, is described. In halothane anaesthetised rats the stem of the right middle cerebral artery was occluded and 3 hours later (with full monitoring of respiratory and cardiovascular status) the animals were killed by perfusion fixation. In normotensive normocapnic animals the volume of infarction was 52 +/- 4 mm3 in the cerebral cortex and 21 +/- 1 mm3 in the corpus striatum. The reproducibility of the volumetric assessment was found to be excellent (coefficient of correlation 0.995 on 18 replicate measurements). The minimum number of stereotactic levels which must be assessed to yield accurate volumetric measurements of infarction is 8. The method is sensitive at detecting alterations in the amount of infarction. For example, it can readily detect the increase in amount of structural damage in cerebral cortex following a transient episode of hypotension. This approach allows an objective assessment of drug therapy and management strategies in the treatment of cerebral infarction.

Is β-APP a marker of axonal damage in short-surviving head injury?

Abstractβ-Amyloid precursor protein (β-APP), a normal constituent of neurons which is conveyed by fast axonal transport, has been found to be a useful marker for axonal damage in cases of fatal head injury. Immunocytochemistry for β-APP is a more sensitive technique for identifying axonal injury than conventional silver impregnation. This study was designed to determine how quickly evidenc of axonal damage and bulb formation appears. Using this method a variety of brain areas were studied from 55 patients who died within 24 h of a head injury. Immunocytochemical evidence of axonal injury was first detected after 2 h survival, axonal bulbs were first identified after 3 h survival, and the amount of axonal damage and axonal bulb formation increased the longer the survival time.

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

SummaryThe 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 pertubation of the axon results in axonal swelling and disconnection at a minimum of 2 h after injury.

Acceleration Induced Head Injury in the Monkey. I. The Model, Its Mechanical and Physiological Correlates

A system has been developed which is capable of inducing brain injuries of graded severity from mild concussion to instantaneous death. A pneumatic shock tester subjects a monkey to a non-impact controlled single sagittal rotation which displaces the head 60 degrees in 10-20 msec. Results derived from 53 experiments show that a good correlation exists between acceleration delivered to the head, the resultant neurological status and the brain pathology. A simple experimental trauma severity (ETS) scale is offered based on changes in the heart rate, respiratory rate, corneal reflex and survivability. ETS grades 1 and 2 show heart rate or respiratory changes but no behavioral or pathological abnormality. ETS grades 3 and 4 have temporary corneal reflex abolition, behavioral unconsciousness, and post-traumatic behavioral abnormalities. Occasional subdural haematomas are seen. Larger forces cause death (ETS 5) from primary apnea or from large subdural haematomas. At the extreme range, instantaneous death (ETS 6) occurs because of pontomedullary lacerations. This model and the ETS scale offer the ability to study a broad spectrum of types of experimental head injury and underscore the importance of angular acceleration as a mechanism of head injury.

Fatal head injury in children.

A comprehensive neuropathological study was undertaken on 87 children aged between 2 and 15 years with fatal head injuries to identify those features which occurred at the time of head injury (fractured skull, contusions, intracranial haematoma and diffuse axonal injury) and those which were subsequently produced by complicating processes (hypoxic brain damage, raised intracranial pressure, infection and brain swelling). The types of brain brain damage identified were remarkably similar to those seen in adults. The only difference was the prevalence of diffuse brain swelling in children.

Glutamate metabotropic and AMPA binding sites are reduced in Alzheimer's disease : an autoradiographic study of the hippocampus

The distribution and levels of glutamate metabotropic binding sites were investigated in the hippocampal region of the human brain using quantitative autoradiography in normal subjects and patients with Alzheimers disease. The topography of glutamate metabotropic binding sites was contrasted with those for kainate and 2-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) in adjacent sections from the same subjects. The regional distribution of glutamate metabotropic binding and AMPA binding were similar, being most abundant in the subiculum and CA1 region and lower in the CA3 region. The distribution of kainate binding differed from that of metabotropic binding being greatest in the deep layers of the parahippocampal gyrus and CA3 and lower in the subiculum and CA1. There were regionally distinct reductions in these non-N-methyl-D-aspartate (non-NMDA) binding sites in patients with Alzheimers disease. Glutamate metabotropic. AMPA and kainate binding were each markedly reduced in the subiculum and the magnitude of the change correlated with neuronal loss within the subiculum. Glutamate metabotropic binding and AMPA binding were reduced significantly in CA1 in subjects with Alzheimers disease whereas kainate binding was minimally altered in this region. Kainate and AMPA binding were reduced significantly in the parahippocampal gyrus in Alzheimers disease while glutamate metabotropic binding was not. In a number of hippocampal areas (e.g. dentate gyrus, CA3), the binding of all ligands was minimally altered in Alzheimers disease. These differences may reflect the localisation of the three types of glutamate binding sites on neuronal elements which are differentially susceptible to the neurodegenerative process of Alzheimers disease.

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

SummaryThere has been controversy for some time as to whether a posttraumatic influx of calcium ions occurs in stretch/non-disruptively 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 Ca2+-ATPase and ecto-Ca-ATPase activity. There is loss of labelling for membrane pump Ca2+-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 Ca2+-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 Ca2+-ATPase activities, results in dissolution of the axonal cytoskeleton and axotomy between 4 and 6 h after the initial insult to axons.