Traumatic axonal injury is exacerbated following repetitive closed head injury in the neonatal pig

Experimental models of repetitive brain injuries

Repetitive traumatic brain injury (TBI) occurs in a significant portion of trauma patients, especially in specific populations, such as child abuse victims or athletes involved in contact sports (e.g. boxing, football, hockey, and soccer). A continually emerging hypothesis is that repeated mild injuries may cause cumulative damage to the brain, resulting in long-term cognitive dysfunction. The growing attention to this hypothesis is reflected in several recent experimental studies of repeated mild TBI in vivo. These reports generally demonstrate cellular and cognitive dysfunction after repetitive injury using rodent TBI models. In some cases, data suggests that the effects of a second mild TBI may be synergistic, rather than additive. In addition, some studies have found increases in cellular markers associated with Alzheimer's disease after repeated mild injuries, which demonstrates a direct experimental link between repetitive TBI and neurodegenerative disease. To complement the findings from humans and in vivo experimentation, my laboratory group has investigated the effects of repeated trauma in cultured brain cells using a model of stretch-induced mechanical injury in vitro. In these studies, hippocampal cells exhibited cumulative damage when mild stretch injuries were repeated at either 1-h or 24-h intervals. Interestingly, the extent of damage to the cells was dependent on the time between repeated injuries. Also, a very low level of stretch, which produced no cell damage on its own, induced cell damage when it was repeated several times at a short interval (every 2 min). Although direct comparisons to the clinical situation are difficult, these types of repetitive, low-level, mechanical stresses may be similar to the insults received by certain athletes, such as boxers, or hockey and soccer players. This type of in vitro model could provide a reliable system in which to study the mechanisms underlying cellular dysfunction following repeated injuries. As this area of TBI research continues to evolve, it will be imperative that models of repetitive injury replicate injuries in humans as closely as possible. For example, it will be important to model appropriately concussive episodes versus even lower level injuries (such as those that might occur during boxing matches). Suitable inter-injury intervals will also be important parameters to incorporate into models. Additionally, it will be crucial to design and utilize proper controls, which can be more challenging than experimental approaches to single mild TBI. It will also be essential to combine, and compare, data derived from in vitro experiments with those conducted with animals in vivo. These issues, as well as a summary of findings from repeated TBI research, are discussed in this review.

Traumatic brain injury in infants: the phenomenon of subdural hemorrhage with hemispheric hypodensity (“Big Black Brain”)

Clinical and experimental studies of traumatic brain injury during immaturity have been far less numerous than those involving adults, and many questions remain about differences in injury responses among patients of different ages. This chapter reviews a distinctive injury pattern common in infants, the so-called "big black brain" response to acute subdural hematoma. The pathophysiology of this injury remains incompletely understood. Insights from both clinical observation and experimental studies have helped to clarify the probable causes of this injury pattern, which appears to require a combination of stressors during a particular period of maturation.

Pediatric traumatic brain injury: quo vadis?

In this review, five questions serve as the framework to discuss the importance of age-related differences in the pathophysiology and therapy of traumatic brain injury (TBI). The following questions are included: (1) Is diffuse cerebral swelling an important feature of pediatric TBI and what is its etiology? (2) Is the developing brain more vulnerable than the adult brain to apoptotic neuronal death after TBI and, if so, what are the clinical implications? (3) If the developing brain has enhanced plasticity versus the adult brain, why are outcomes so poor in infants and young children with severe TBI? (4) What contributes to the poor outcomes in the special case of inflicted childhood neurotrauma and how do we limit it? (5) Should both therapeutic targets and treatments of pediatric TBI be unique? Strong support is presented for the existence of unique biochemical, molecular, cellular and physiological facets of TBI in infants and children versus adults. Unique therapeutic targets and enhanced therapeutic opportunities, both in the acute phase after injury and in rehabilitation and regeneration, are suggested.

Large animal models of traumatic injury to the immature brain

Large animal models have been used much less frequently than rodent models to study traumatic brain injury. However, large animal models offer distinct advantages in replicating specific mechanisms, morphology and maturational stages relevant to age-dependent injury responses. This paper reviews how each of these features is relevant in matching a model to a particular scientific question and discusses various scaling strategies, advantages and disadvantages of large animal models for studying traumatic brain injury in infants and children. Progress to date and future directions are outlined.

Heavy neurofilament accumulation and alpha-spectrin degradation accompany cerebellar white matter functional deficits following forebrain fluid percussion injury

Evidence for diffuse traumatic axonal injury (TAI) in clinical cases and animal models of traumatic brain injury (TBI) indicate that pathophysiological mechanisms extend to regions remote from the injury epicenter. The potential for indirect cerebellar trauma contributing to TBI pathophysiology is of significance since impairment of motor function and coordination is a common consequence of TBI but is also a domain associated with cerebellar function. The relationship between cerebellar white matter structure and function following traumatic head injury has not been examined. Using the fluid percussion injury (FPI) device applied unilaterally in the forebrain, evoked compound action potential (CAP) recordings from cerebellar white matter of Sprague-Dawley rats indicated a spatial and temporal pattern of electrophysiological deficits throughout the cerebellar vermis. The posterior and middle lobules of the cerebellum exhibited significant declines in evoked CAP amplitude compared to sham controls (p=0.004, p=0.005, respectively). Duration of the CAP decay also increased, suggesting that functional white matter deficits were a combination of axonal loss and compromised axonal integrity. Functional white matter deficits persisted at 14 days post-injury in the posterior and middle regions of the cerebellum. Evidence of heavy chain neurofilament (NF200) degradation was observed at 1 day post-injury by Western blot. Immunohistochemistry labeling for NF200 indicated the presence of highly immunoreactive NF200 axonal swellings consistent with morphological features of TAI. alpha-Spectrin degradation was also observed between 1 and 14 days post-injury. This study demonstrates the electrophysiological consequences of cerebellar white matter injury and a temporal profile of NF200 and spectrin degradation following forebrain FPI.

Shaken Baby Syndrome

Unfortunately, head trauma caused by shaken baby syndrome is a common occurrence in infants and young children. The proper treatment and safety of these children can be enhanced by the nurse's ability to recognize features characteristic of this syndrome. If abuse is suspected, appropriate physicians, child-protective, and law-enforcement agencies should be notified immediately. Further research must be done to improve the understanding of the mechanisms associated with this disorder in the ultimate hope of improving the lives and outcome of infants and children.

Predicting Unconsciousness from a Pediatric Brain Injury Threshold

The objective of this study was to utilize tissue deformation thresholds associated with acute axonal injury in the immature brain to predict the duration of unconsciousness. Ten anesthetized 3- to 5-day-old piglets were subjected to nonimpact axial rotations (110-260 rad/s) producing graded injury, with periods of unconsciousness from 0 to 80 min. Coronal sections of the perfusion-fixed brain were immunostained with neurofilament antibody (NF-68) and examined microscopically to identify regions of swollen axons and terminal retraction balls. Each experiment was simulated with a finite element computational model of the piglet brain and the recorded head velocity traces to estimate the local tissue deformation (strain), the strain rate and their product. Using thresholds associated with 50, 80 and 90% probability of axonal injury, white matter regions experiencing suprathreshold responses were determined and expressed as a fraction of the total white matter volume. These volume fractions were then correlated with the duration of unconsciousness, assuming a linear relationship. The thresholds for 80 and 90% probability of predicting injury were found to correlate better with injury severity than those for 50%, and the product of strain and strain rate was the best predictor of injury severity (p=0.02). Predictive capacity of the linear relationship was confirmed with additional (n=13) animal experiments. We conclude that the suprathreshold injured volume can provide a satisfactory prediction of injury severity in the immature brain.

Initial neurologic presentation in young children sustaining inflicted and unintentional fatal head injuries

BACKGROUND

It remains unclear if fatal brain injuries in young children are characterized by immediate rapid deterioration or can present after an initial period of lucidity. This issue has legal implications in child abuse, for which understanding the clinical course affects perpetrator identification.

OBJECTIVE

To determine patterns of neurologic presentation on hospital admission in infants and toddlers who die of inflicted and unintentional injury.

DESIGN/METHODS

Data on children <48 months of age who sustained a fatal head injury from 1986-2002 were extracted from the Pennsylvania Trauma Outcomes Study. Only those with external-causes-of-injury codes for inflicted injury, falls, and motor vehicle crashes (MVCs) with a recorded Glasgow Coma Scale (GCS) on admission were included. The GCS was compared across mechanisms and age groups (0-11, 12-23, 24-35, and 36-47 months).

RESULTS

Of the 314 fatally injured children, 37% sustained inflicted injury, 13% sustained a fall, and 49% sustained an MVC. At admission, 6.8% of all children had a GCS score of >7, and 1.9% presented with a GCS score of >12 (lucid). The incidence of admission a GCS score of >7 varied by mechanism. Overall, children with inflicted injury were 3 times more likely to present with a GCS score of >7 than those injured in MVCs (odds ratio [OR]: 3.6; 95% confidence interval [CI]: 1.2-10.3), but incidence of a GCS score of >7 did not differ between inflicted injuries and falls. Similarly, when considering only those children >or=24 months old, a GCS score of >7 did not differ by mechanism. In contrast, in those <24 months old, children who died as a result of inflicted injury were >10 times more likely to have a GCS score of >7 than those who died as a result of a MVC (OR: 9.36; 95% CI: 1.3-80.9).

CONCLUSIONS

The data suggest an age- and mechanism-dependent presentation of neurologic status in children with fatal head injury. Although infrequent, young victims of fatal head trauma may present as lucid (GCS score: >12) before death. Furthermore, children <48 months old sustaining inflicted injury are 3 times more likely to be assessed with a moderate GCS score (>7) than those in MVCs. This effect is amplified in the youngest children (<24 months old): those with inflicted injury were 10 times more likely to present with moderate GCS scores than those in MVCs. In addition, this youngest age group seems to be overrepresented in those who present as lucid (GCS score: >12 [5 of 6]). It is unclear whether these differences are the result of inadequate tests to evaluate consciousness in younger children or differences in biomechanical mechanisms of inflicted trauma.