An overview of inflicted head injury in infants and young children, with a review of beta-amyloid precursor protein immunohistochemistry

Abusive Head Trauma Animal Models: Focus on Biomarkers

Abusive head trauma (AHT) is a serious traumatic brain injury and the leading cause of death in children younger than 2 years. The development of experimental animal models to simulate clinical AHT cases is challenging. Several animal models have been designed to mimic the pathophysiological and behavioral changes in pediatric AHT, ranging from lissencephalic rodents to gyrencephalic piglets, lambs, and non-human primates. These models can provide helpful information for AHT, but many studies utilizing them lack consistent and rigorous characterization of brain changes and have low reproducibility of the inflicted trauma. Clinical translatability of animal models is also limited due to significant structural differences between developing infant human brains and the brains of animals, and an insufficient ability to mimic the effects of long-term degenerative diseases and to model how secondary injuries impact the development of the brain in children. Nevertheless, animal models can provide clues on biochemical effectors that mediate secondary brain injury after AHT including neuroinflammation, excitotoxicity, reactive oxygen toxicity, axonal damage, and neuronal death. They also allow for investigation of the interdependency of injured neurons and analysis of the cell types involved in neuronal degeneration and malfunction. This review first focuses on the clinical challenges in diagnosing AHT and describes various biomarkers in clinical AHT cases. Then typical preclinical biomarkers such as microglia and astrocytes, reactive oxygen species, and activated N-methyl-D-aspartate receptors in AHT are described, and the value and limitations of animal models in preclinical drug discovery for AHT are discussed.

The clinical utility of proton magnetic resonance spectroscopy in traumatic brain injury: recommendations from the ENIGMA MRS working group

Proton (1H) magnetic resonance spectroscopy provides a non-invasive and quantitative measure of brain metabolites. Traumatic brain injury impacts cerebral metabolism and a number of research groups have successfully used this technique as a biomarker of injury and/or outcome in both pediatric and adult TBI populations. However, this technique is underutilized, with studies being performed primarily at centers with access to MR research support. In this paper we present a technical introduction to the acquisition and analysis of in vivo 1H magnetic resonance spectroscopy and review 1H magnetic resonance spectroscopy findings in different injury populations. In addition, we propose a basic 1H magnetic resonance spectroscopy data acquisition scheme (Supplemental Information) that can be added to any imaging protocol, regardless of clinical magnetic resonance platform. We outline a number of considerations for study design as a way of encouraging the use of 1H magnetic resonance spectroscopy in the study of traumatic brain injury, as well as recommendations to improve data harmonization across groups already using this technique.

Pathophysiological and behavioral deficits in developing mice following rotational acceleration-deceleration traumatic brain injury

Abusive head trauma (AHT) is the leading cause of death from trauma in infants and young children. An AHT animal model was developed on 12-day-old mice subjected to 90° head extension-flexion sagittal shaking repeated 30, 60, 80 and 100 times. The mortality and time until return of consciousness were dependent on the number of repeats and severity of the injury. Following 60 episodes of repeated head shakings, the pups demonstrated apnea and/or bradycardia immediately after injury. Acute oxygen desaturation was observed by pulse oximetry during respiratory and cardiac suppression. The cerebral blood perfusion was assessed by laser speckle contrast analysis (LASCA) using a PeriCam PSI system. There was a severe reduction in cerebral blood perfusion immediately after the trauma that did not significantly improve within 24 h. The injured mice began to experience reversible sensorimotor function at 9 days postinjury (dpi), which had completely recovered at 28 dpi. However, cognitive deficits and anxiety-like behavior remained. Subdural/subarachnoid hemorrhage, damage to the brain-blood barrier and parenchymal edema were found in all pups subjected to 60 insults. Proinflammatory response and reactive gliosis were upregulated at 3 dpi. Degenerated neurons were found in the cerebral cortex and olfactory tubercles at 30 dpi. This mouse model of repetitive brain injury by rotational head acceleration-deceleration partially mimics the major pathophysiological and behavioral events that occur in children with AHT. The resultant hypoxia/ischemia suggests a potential mechanism underlying the secondary rotational acceleration-deceleration-induced brain injury in developing mice.

A Conceptual Overview of Axonopathy in Infants and Children with Allegedly Inflicted Head Trauma

Fatal, allegedly inflicted pediatric head trauma remains a controversial topic in forensic pathology. Recommendations for systematic neuropathologic evaluation of the brains of supposedly injured infants and children usually include the assessment of long white matter tracts in search of axonopathy - specifically, diffuse axonal injury. The ability to recognize, document, and interpret injuries to axons has significant academic and medicolegal implications. For example, more than two decades of inconsistent nosology have resulted in confusion about the definition of diffuse axonal injury between various medical disciplines including radiology, neurosurgery, pediatrics, neuropathology, and forensic pathology. Furthermore, in the pediatric setting, acceptance that "pure" shaking can cause axonal shearing in infants and young children is not widespread. Additionally, controversy abounds whether or not axonal trauma can be identified within regions of white matter ischemia - a debate with very significant implications. Immunohistochemistry is often used not only to document axonal injury, but also to estimate the time since injury. As a result, the estimated post-injury interval may then be used by law enforcement officers and prosecutors to narrow "exclusive opportunity" and thus, identify potential suspects. Fundamental to these highly complicated and controversial topics is a philosophical understanding of the diffuse axonal injury spectrum disorders.

β-Amyloid Precursor Protein and Ubiquitin Immunohistochemistry Aid in the Evaluation of Infant Autopsy Eyes With Abusive Head Trauma

PURPOSE

To investigate β-amyloid precursor protein (β-APP), ubiquitin, and glial fibrillary acid protein (GFAP) immunostaining as a diagnostic tool to aid in the discrimination between abusive head trauma and nonabusive head trauma in postmortem ocular histopathologic investigation.

DESIGN

Retrospective cross-sectional study.

METHODS

Seventy-four eyes of 37 infants were studied for hemorrhage and immunohistochemical expression of β-APP, ubiquitin, and GFAP in the retina and optic nerve. Infants were assigned to abusive head trauma or control groups, according to published criteria.

RESULTS

In the abusive head trauma group, positive β-APP and ubiquitin immunostaining of the retina was significantly more likely to be found than in the control group, odds ratio (OR) 11.4, confidence interval (CI) 2.9-44.3; P < .001 and OR 8.8, CI 2.2-34.5; P = .002, respectively. Positive correlations were found between retinal expression of β-APP and ubiquitin immunostaining and retinal hemorrhage. Vitreal hemorrhages, orbital fat hemorrhages, and macular folds could only be identified in abusive head trauma cases. Retinal hemorrhages were significantly more severe, occupied a larger proportion of the retina, and involved more retinal layers in abusive head trauma compared to controls (OR 2.7, CI 1.7-4.4; P < .001).

CONCLUSIONS

This study shows correlations between positive retinal β-APP and ubiquitin immunostaining as a sign of axonal injury in abusive head trauma. Axonal injury is a useful pathologic feature that can be demonstrated in postmortem ocular investigation of deceased children using immunohistochemical staining for β-APP and ubiquitin with a high OR for abusive head trauma when compared to controls.

Expression of amyloid-β protein and amyloid-β precursor protein after primary brain-stem injury in rats

Amyloid-β (Aβ) protein and its precursor, amyloid-β precursor protein (β-APP), have traditionally been used in the diagnosis of Alzheimer disease. Their use in diagnosis of traumatic brain injury by forensic analysis is becoming more widespread. However, to date, no reliable small animal model exists to evaluate these brain injury indicators. To address this, we have studied primary brain-stem injury in rats to assess the appearance of diffuse axonal injury in brain sections and correlate these findings with appearance of Aβ and relative β-APP mRNA levels. Using an EnVision 2-step immunohistochemical staining method to measure axon diameter, we found that there was significant difference in axon diameters within the medulla oblongata and several time points after brain injury, ranging from 3 to 24 hours. In addition, mRNA expression levels of β-APP increased following brain injury, peaking 3 hours following injury and decreasing back to baseline levels by 24 hours after injury. These results suggest that using immunohistochemistry and reverse transcription-polymerase chain reaction to detect changes in Aβ-associated axonal changes and β-APP mRNA levels, respectively, can be useful for the diagnosis of diffuse axonal injury during autopsy at early time points following fatal brain injury.

Traumatic brain injury, axonal injury and shaking in New Zealand sea lion pups

Trauma is a common cause of death in neonatal New Zealand sea lion pups, and subadult male sea lions have been observed picking up and violently shaking some pups. In humans, axonal injury is a common result of traumatic brain injury, and can be due to direct trauma to axons or to ischaemic damage secondary to trauma. 'Shaken baby syndrome', which has been described in human infants, is characterised by retinal and intracranial subdural haemorrhages, and has been associated with axonal injury to the brain, spinal cord and optic nerve. This study identifies mechanisms of traumatic brain injury in New Zealand sea lion pups, including impact injuries and shaking-type injuries, and identifies gross lesions of head trauma in 22/36 sea lion pups found dead at a breeding site in the Auckland Islands. Despite the high frequency of such gross lesions, only three of the pups had died of traumatic brain injury. Observational studies confirmed that shaking of pups occurred, but none were shown to die as a direct result of these shaking events. Axonal injury was evaluated in all 36 pup brains using β-amyloid precursor protein immunohistochemistry. Immunoreactive axons were present in the brains of all pups examined including seven with vascular axonal injury and two with diffuse axonal injury, but the severity and pattern of injury was not reliably associated with death due to traumatic brain injury. No dead pups had the typical combination of gross lesions and immunohistochemical findings that would conform to descriptions of 'shaken baby syndrome'. Axonal injury was present in the optic nerves of most pups, irrespective of cause of death, but was associated with ischaemia rather than trauma.

Year in review 2010: Critical Care--Neurocritical care

In 2010 Critical Care published a large number of articles on critical care aspects of neurologic and neurosurgical conditions. These aspects included investigation of diagnostic criteria for bacterial meningitis, critical illness myopathy and their relationship to systemic inflammation. A number of studies investigated the biology of sepsis-related delirium, its biomarkers, its relationship to inflammation and its impact on outcome. Other teams reported on the use of magnetic resonance imaging, biomarkers and electroencephalogram to predict outcome in patients who were comatose following cardiac arrest. Our understanding of the pathophysiology as well as management of subarachnoid hemorrhage was addressed in several papers. Topics included the effect of hemodynamic treatment of delayed cerebral ischemia, pulmonary edema and the impact of subarachnoid hemorrhage on endocrine function. Finally, outcome from neurocritical care and patients' retrospective willingness to consent to the treatment they received were reported.

Spinal nerve root β-APP staining in infants is not a reliable indicator of trauma

This preliminary communication describes seven babies with β-amyloid precursor protein (βAPP) positive axonal swellings in nerve roots at multiple levels of the spinal cord. All seven babies died of natural causes. Two died in utero providing evidence for nerve root injury in the absence of trauma, two died within one day of birth and the possibility of birth related injury has to be considered. Three babies were over one month of age and had no history or pathological evidence of trauma. These findings show that if axonal injury is carefully sought in every infant death, not just in babies where trauma is suspected, it will be found in a proportion of babies dying from natural diseases. While spinal nerve root axonal injury in infants may suggest trauma, it is not, in itself, diagnostic of trauma.

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.

Magnetic resonance spectroscopy predicts outcomes for children with nonaccidental trauma

OBJECTIVE

We evaluated proton magnetic resonance spectroscopic imaging (MRSI) findings for children with traumatic brain injury attributable to nonaccidental trauma (NAT) early after injury, to determine whether brain metabolite changes predicted outcomes.

METHODS

Proton MRSI (1.5 T) was performed (mean: 5 days after injury [range: 1-30 days]) through the level of the corpus callosum for 90 children with confirmed NAT. Regional N-acetylaspartate/total creatine, N-acetylaspartate/total choline, and choline/creatine ratios and the presence of lactate were measured. Data on long-term outcomes defined at > or =6 months were collected for 44 of 90 infants. We grouped patients into good (normal, mild disability, or moderate disability; n = 32) and poor (severe disability, vegetative state, or dead; n = 12) outcome groups.

RESULTS

We found that N-acetylaspartate/creatine and N-acetylaspartate/choline ratios (mean total, corpus callosum, and frontal white matter) were significantly decreased in patients with poor outcomes (P < .001). A logistic regression model using age, initial Glasgow Coma Scale score, presence of retinal hemorrhage, lactate on MRSI scans, and mean total N-acetylaspartate/creatine ratio predicted outcomes accurately in 100% of cases.

CONCLUSIONS

Reduced N-acetylaspartate levels (ie, neuronal loss/dysfunction) and elevated lactate levels (altered energy metabolism) correlated with poor neurologic outcomes for infants with NAT. Elevated lactate levels may reflect primary or secondary hypoxic-ischemic injury, which may occur with NAT. Our data suggest that MRSI performed early after injury can be used for long-term prognosis.

Fatal head injury in children younger than 2 years in New York City and an overview of the shaken baby syndrome

CONTEXT

Shaken baby syndrome is a controversial topic in forensic pathology. Some forensic pathologists state that shaking alone is insufficient to explain death and that an impact must have occurred even if there is no impact site on the head.

OBJECTIVE

To examine a large cohort of fatal, pediatric head injuries for patterns of specific autopsy findings and circumstances that would support or dispute pure shaking as the cause of death.

DESIGN

We retrospectively reviewed 59 deaths due to head injuries in children younger than 2 years certified in our office during a 9 year period (1998-2006). The review included autopsy, toxicology, microscopy, neuropathology, and police and investigators' reports.

RESULTS

There were 46 homicides, 8 accidents, and 1 undetermined death from blunt-impact injury of the head. In 10 (22%) of the homicides, there was no impact injury to the head, and the cause of death was certified as whiplash shaking. In 4 (40%) of these 10 deaths, there was a history of shaking. In 5 (83%) of the other 6, there was no history of any purported accidental or homicidal injury. All 8 accidental deaths had impact sites. Of the 59 deaths, 4 (6.7%) had only remote injuries (chronic subdural hematomas, remote long bone fractures) that were certified as undetermined cause and manner. These 4 deaths were excluded from the study.

CONCLUSIONS

We describe a subset of fatal, nonaccidental head-injury deaths in infants without an impact to the head. The autopsy findings and circumstances are diagnostic of a nonimpact, shaking mechanism as the cause of death. Fatal, accidental head injuries in children younger than 2 years are rare.

Inflicted traumatic brain injury in infants and young children

This article will discuss the subject of inflicted or abusive head injury in infants and young children. Inflicted neurotrauma is a very common injury and a frequent problem in attempting to distinguish between inflicted and accidental injury. Inflicted head injury occurs usually in the home in the presence of the individual who has inflicted the injury outside the view of unbiased witnesses. Distinguishing between inflicted and accidental injury may be dependent upon the pathological findings and consideration of the circumstances surrounding the injury. The most common finding in an inflicted head injury is the presence of subdural hemorrhage. Subdural hemorrhage may occur in a variety of distributions and appearances. The natural history of subdural bleeding and the anatomy of the "subdural" will be considered. The anatomy of the dura and its attachment to the skull and to the arachnoid determines how subdural bleeding evolves into the cleaved dural border cell layer and as well as how bridging veins are torn and anatomically where bleeding will occur. Different biomechanical mechanisms result in different distributions of subdural blood and these differences will be discussed.

Delayed homicides due to infant head injury initially reported as natural (cerebral palsy) deaths

A spectrum of neuropathology occurs in infants who sustain traumatic brain injury. Because of a prolonged survival interval, there is a risk that these deaths may not be recognized as a sequel of trauma. We reviewed the records in New York City of 5 delayed fatalities due to nonaccidental infant head injury that had survival intervals from 2.5 to 17 years. The head injuries occurred at 2 to 3 months of age, and death occurred at 2.5 to 17 years of age. Initially, they were reported as natural deaths by treating physicians, families, and/or police. All 5 infants had unexplained or poorly explained remote traumatic head injury that included subdural hematomas. At autopsy, the neuropathologic exam demonstrated remote subdural hemorrhages and lesions related to chronic hypoxic-ischemic injury including atrophy, arterial infarcts, border-zone infarcts, and cystic encephalomalacia. Each child survived the initial injury but later succumbed to the delayed effects of secondary hypoxic-ischemic encephalopathy. These 5 deaths highlight the need to investigate independently the medical history of any child (or adult) who dies with a clinical diagnosis of "cerebral palsy." The term cerebral palsy often is used as a catchall for any patient who has had neurologic impairment since infancy or childhood. If there is a direct link between the initial injury and the death, even if the injury occurred many years before death, then the injury is the proximate cause of death and dictates the manner of death. All 5 deaths were certified as homicides.