What are the characteristics and consequences of childhood traumatic brain injury? - Chapter 9

Childhood traumatic brain injury (TBI) is a common cause of interruption to normal development. Depending on its severity, TBI may result in residual impairments in various skills, in particular information processing, attention, memory, learning, and social cognition. These deficits may adversely impact the capacity of the child to interact with the environment effectively, which in turn leads to lags in skill acquisition and increasing gaps between brain injured children and their peers. Studies focused on long-term follow-up of these children and their families found that, even with access to excellent rehabilitation resources, problems persist, although the nature of these problems changes with time after insult as well as with the developmental level of the child. It is difficult to predict the (long-term) outcomes of TBI, as the long-term consequences depend on a complex interaction of various factors, such as premorbid child abilities, socio-emotional functioning, characteristics of the brain injury, the environmental context, developmental stage of the child, access to rehabilitation, as well as factors yet to be identified. TBI is not equally common across the population; children with disadvantageous backgrounds and those with pre-existing behavioural and developmental impairments are are greater risk of both injury and poor recovery. Additional risk factors are post-injury parent and family stress and reduced or limited access to early intervention and support services. 

What is currently known about the epidemiology of childhood traumatic brain injury?

Gathering information about the incidence and prevalence of TBI is challenging. Epidemiological studies vary with respect to definitions of the injury, data sources, data collection techniques, case descriptions, and ages of target populations. Overall, population estimates point towards 250 - 799 cases per 100,000 per year. Approximately 80% of these refer to mild injuries, half of whom will not seek any medical care. Between 5-10% will experience temporary and/or permanent neuropsychological consequences, and another 5-10% will receive fatal injuries. Approximately one in every 30 new-born children will sustain a TBI before age 16.

Across the lifespan, the most common causes of TBI are transportation-related accidents and falls. Together, they account for more than half of all childhood TBI. The nature of these accidents and falls differs for various developmental stages. Infants and toddlers are most likely to experience TBI through falls or via inflicted injuries secondary to child abuse. Young children are most likely to experience TBI through falls and motor vehicle collisions, either as occupants or pedestrians. Older children are most likely to experience TBI through sports and recreational accidents and pedestrian or bicycle collisions with motor vehicles. Adolescents are most likely to experience TBI through motor vehicle collisions and competitive sports.

An important risk factor for the prognosis of TBI is age. Mortality and morbidity increase as age decreases. One study found a mortality rate of 50% for children experiencing TBI before the age of two, compared to only 14% for those injured after age 14. Another risk factor is age. Boys are at greater risk of sustaining TBI than girls, over the entire childhood. Another influential factor is timing. Child TBI is more likely to occur on the weekends, holidays, and afternoons, when children are out of school and involved in leisure activities.

What is currently known about the neuropathology and pathophysiology of childhood traumatic brain injury?

TBI is typically caused by a physical blow or wound to the head that is sufficient to result in altered consciousness and may lead to neurological or neurobehavioural sequelae. Although TBI is commonly characterised as a unitary entity, the mechanisms and underlying pathophysiology associated with these injuries vary significantly, resulting in a wide range of potential consequences. These consequences can be determined by various factors:

1. The force of the impact.
2. The intracranial vectors of transmitted force, that is linear or rotational.
3. The thickness of the scalp and skull.
4. The site of impact.
5. The presence or absence of skull fracture. Generally, it can be said that the greater the force applied, the more severe the associated damage. 

The most common form of TBI is closed head injury in which the brain is shaken within the skull cavity, resulting in diffuse axonal damage and multiple injury sites, but with the skull remaining intact. Closed head injury accounts for approximately 90% of all cases of childhood TBI. The remaining 10% of injuries come from penetrating injuries, which comprise penetration of the skull by some form of 'missile', frequently a bullet, rock, or knife. This is also associated with a risk of cerebral infection, swelling, bleeding, and raised intracranial pressure. Brain swelling, also called cerebral oedema, refers to an increase in fluid volume within the skull. This may occur either due to a failure of the auto regulatory mechanism of cerebral blood flow due to hypoxia, hypercapnia, or obstruction to cerebral circulation, or it may occur due to increased fluid within the brain associated with a range of possible causal factors, including obstruction of cerebrospinal fluid flow and increased intravascular pressure or damage to blood vessels. Brain swelling may occur regionalised or diffuse. 

Brain damage resulting from TBI involves processes that are more complex, prolonged, and interwoven than previously thought. The consequences of childhood TBI differ from those observed in adults, because the immature brain responds differently to trauma than the mature brain does. The pathophysiology of TBI is classified on the basis of the initial injury. Primary injuries occur as a direct result of the impact of force on the brain and include fractures, contusions, and lacerations. Primary injuries are typically permanent and show little response to early treatment. Secondary injuries occur as a consequence of the primary injury. Two common types of secondary injuries are raised intracranial pressure and brain swelling. Other forms of secondary injuries are: hypoxia, infection, metabolic changes including hypothermia, electrolyte imbalance, and respiratory difficulties.

Mass effects (haematomas), which are caused by vascular interruptions, are not very common in children. However, if not treated quickly (usually through surgical evacuation), such secondary complications can lead to cerebral herniation and ultimately death. Different types of haematomas are common to TBI. Epidural haematomas refer to bleeds just below the skull surface, above the dura. These doe not directly involve brain tissue and mostly occur in the context of skull fracture, where vessels in the meninges are damaged. Subdural haematomas refer to blood accumulation between the dura and the arachnoid mater. These occur more frequently than epidural haematomas and are also more serious. Lastly, intracerebral haematomas occur within brain parenchyma and follow the same spatial distribution as contusions. If treated promptly, the outcome from these complications is positive. However, if left untreated, increasing blood mass may cause cerebral shift and herniation.

The type of insult and corresponding neuropathology are summarised in the table below.

What are important components in diagnosis and early recovery?

Childhood TBI can cause significant impairments in a variety of domains, including alertness, orientation, motor function, language, communication, non-verbal skills, attention, memory, and executive functions. These functional deficits are typically evident in the acute stages post-TBI, once the child regains consciousness and becomes alert and orientated. 

Evaluation and treatment of childhood TBI begins at the scene of the jury, where the state of consciousness and the neurological status are assessed. By the time the child reaches the hospital, he or she will already have sustained permanent primary impact-related brain injury. Secondary effects will also begin to manifest and may warrant medical intervention. Early treatment is very much focused on accurate identification of these secondary effects and their rapid treatment. Important markers at this stage are: level of consciousness, clinical evidence of skull fracture or cerebral pathology, and neurological and mental status. Level of consciousness forms the most important measure of assessing the severity of the injury. A further measure of severity is post-traumatic amnesia (PTA) duration. PTA refers to the period of confusion and disorientation following the injury or emergence from coma. This period is characterised by attentional impairment and memory disturbance. 

Important techniques in assessing the brain pathology are provided by brain imaging, in particular computed tomography (CT) scans, structural magnetic resonance imaging (MRI), diffusion weighted imaging (DWI) or diffusion tensor imaging (DTI), susceptibility weighted imaging (SWI), magnetic resonance spectroscopy (MRS), functional MRI (fMRI) and functional connectivity, quantitative methods for structural MRI, and near-infrared spectroscopy (NIRS). 

• Computed tomography (CT) scans are useful for clinical decision making, because they rapidly detect lesions that need immediate medical intervention, such as large haematomas or skull fractures. 
• Structural magnetic resonance imaging (MRI) makes use of a magnetic field strength to align atoms in the body. Radio frequency pulses are emitted to alter this alignment, causing nuclei to produce a rotating magnetic field detected by the scanned and reconstructed into images. MRI scans are more sensitive than CT scans, in particular for detecting diffuse axon injury (DAI). In addition, MRI scans have a reduced risk of radiation exposure in comparison to CT scans.
• Diffusion weighted imaging (DMI) and diffusion tensor imaging (DTI) are particularly useful for assessing the integrity of white matter, including damage or degeneration of white matter fibres through breakdown of myelin and nerve terminals, or neuronal swelling or shrinkage. 
• Susceptibility weighted imaging (SWI) is a specific MRI technique that exploits the magnetic susceptibility differences between tissues. It is beneficial for lesion detection, making it useful for identifying micro haemorrhages and other small, diffuse lesions that are typical for traumatic or diffuse axonal injury.
• Magnetic resonance spectroscopy (MRS) measures the relative concentration of metabolites in brain tissue using spectroscopic analysis. MRS can provide additional neuropathological information that is useful in predicting recovery following childhood TBI.
• Functional MRI (fMRI) makes use of the blood oxygen level-dependent (BOLD) technique to measure cerebral activity, often in response to stimulation. Although fMRI has diagnostic potential, it is generally not part of clinical practice. 
• Quantitative methods for structural MRI quantify brain volume or voxel-based morphometry. They provide information on the structural integrity of regions of interest in the brain. These methods have been used extensively in assessing brain pathology in childhood TBI.
• Near-infrared spectroscopy (NIRS) refers to a portable, relatively non-invasive technique that can be used to assess brain function by detecting changes in blood haemoglobin levels associated with neural activity via use of infrared light. NIRS has particular benefits for infants and young children who are difficult to assess via CT or MRI scans without sedation. It also has the potential to associate brain activity in response to stimulation. A disadvantage of NIRS is that near-infrared light is not capable to penetrate to the level of subcortical structures, hence it is restricted to use at the cortical level. 

What are the stages of recovery following childhood TBI?

Although outcome is difficult to predict, the stages of recovery following childhood TBI follow a relatively routine path depending on the severity of the brain injury. A distinction here is made between the rather rapid and uncomplicated recovery following mild brain injury, in which residual sequelae are minimal, and the more protracted process that follows from moderate and severe TBI, in which extended hospitalisation and ongoing rehabilitation may be needed.

Recovery after mild TBI

Directly after mild TBI (mTBI), there is a short period of altered consciousness, possibly even with loss of consciousness. This period is usually associated with symptoms of confusion and disorientation. Typically, children are observed for a brief period and discharged home without hospitalisation. In the following days, there is a high risk of post-concussive symptoms characterised by transient impairments in cognition (memory, attention, executive function, and processing speed), physical condition (fatigue, headache, nausea), and psychological condition (irritability, mood change, and emotional dysregulation). These post-concussive symptoms tend to reflect more cognitive problems and are more persistent in children compared to adults experiencing TBI. In fact, there appears to be a delayed recovery pattern in children and adolescents post-mTBI in approximately 20% of the sufferers, which is not yet well understood. Characteristic consequences of mTBI are: reduced attention, slowed response speeds, impaired memory, fatigue, and irritability. Note that these skills are crucial for daily activities, including acquiring new knowledge and skills as well as attending to school work. In addition to these cognitive problems, children with mTBI may also experience behavioural difficulties post-concussion, including headache, pressure in the head, dizziness, fatigue, sleep disturbance, restlessness, sensitivity to noise and vision, blurred or double vision, nausea, and tinnitus. With regard to the long-term consequences, there is some controversy in the literature. Some studies found few, if any, impairments in intellectual ability, attention, or memory function. Others found a significant subgroup of injured children (up to 30%) that failed to achieve full symptom resolution, exhibiting psychological and cognitive difficulties. The suggestion has been made to divide this group into mild and mild-complicated categories to aid diagnosis and prognosis. 

Recovery after moderate and severe TBI

Recovery from moderate and severe TBI is more prolonged than from mild TBI and may be seen as a multi-phase process where there is an interaction between the physical recovery of the child, its developmental level, the family response, and the reintegration of the child back into society. Typically, children with moderate of severe TBI are hospitalised for some time. During this time, the child's progress is carefully monitored for evidence of deterioration caused by raised intracranial pressure or haematoma, which would require surgery. At this stage, physical rehabilitation starts, focused on maintaining the child's physical strength and on basic activities such as feeding. During this stage, there is a high degree of anxiety for the family, caused by the concern about their child's survival. After the child emerges from coma, fears for survival diminish and active rehabilitation begins. During this stage, the child may appear restless, agitated, confused, and disorientated. Functional impairments will become evident. More intensive rehabilitation begins, including physical and speech therapy. The goal is to be able to return home to a familiar environment. After discharge, the child continues to receive regular rehabilitation. Returning to school is typically a gradual process, starting with attending school for short periods, primarily for social contact, and then extending this period by attending more classes as the child gains physical strength. This stage requires a degree of balancing between rehabilitation goals, needs of social adjustment of the child and school, and family resources. It requires effective communication between therapists, children, and families. Some children demonstrate a relatively full recovery after more severe TBI, whereas others demonstrate ongoing residual impairments, necessitating life-long medical and rehabilitation involvement. 

What are the neurobehavioural and functional consequences of childhood traumatic brain injury?

Childhood traumatic brain injury is associated with a wide range of neurobehavioural and functional consequences:

• Impaired intellectual functioning.
• Impaired language and communication skills (e.g., expressive and receptive language deficits, word-finding difficulties, and complex comprehension deficits).
• Impaired non-verbal and motor skills (fine motor coordination, reduced motor control, and motor planning).
• Deficits in attention and information processing skills (these are the hallmarks of severe TBI).
• Memory impairment (difficulties acquiring knowledge and learning).
• Deficits in executive functions (e.g., planning and mental flexibility).
• Impaired socio-emotional skills (social dysfunction).
• Behavioural and psychiatric disorders.
• Academic difficulties (inability to cope in standard classrooms, declines in performance).

What are predictors of outcome?

Although it is difficult to predict outcome following childhood traumatic brain injury, some predictors have been identified that may play a role in the process. First, injury severity is a well-established predictor of outcome following TBI. There is overall agreement that moderate to severe TBI results in substantial and persistent morbidity, whereas mTBI is more benign. Second, age at injury is an predictor of outcome. While not identified in the case of mTBI, current evidence demonstrates that young children sustaining generalised brain insult are at an elevated risk for long-term cognitive deficits. Third, recent research has begun to focus on non-injury related factors, including premorbid attention problems, increasing the risk of post-injury attention problems among children with severe TBI. Other, environmental, factors are also considered to be important for outcome following TBI, including socio-economic status and several family demographics, measures of parent mental health, family function, and family burden. 

How to treat childhood traumatic brain injury?

Treatment and management of TBI requires long-term clinical involvement. The role of the psychologist here is multidimensional, being responsible for monitoring neurobehavioural recovery, understanding the strengths and weaknesses of the child, communicating with teachers and rehabilitation workers, designing cognitive interventions and behavior management programmes, providing counseling with regard to adjustment issues for the child and family, and informing parents and others in the wider community about the implications of the child's injuries for daily functioning. At the clinical level, families are involved with therapists to identify meaningful goals for rehabilitation. One study demonstrated that children who received home-based cognitive, behavioural, and physical intervention from their parents had significantly improved outcomes in comparison to children who received routine hospital-based rehabilitation.