Brain injury

In medicine, brain injuries are "acute and chronic injuries to the brain, including the cerebral hemispheres, cerebellum, and brain stem. Clinical manifestations depend on the nature of injury. Diffuse trauma to the brain is frequently associated with diffuse axonal injury or coma, post-traumatic. Localized injuries may be associated with neurobehavioral manifestations; hemiparesis, or other focal neurologic deficits.."

Types of brain injury include:

• Diffuse axonal injury
• Brain concussion
• Minimal brain injury which may be defined at abnormal x-ray computed tomography of the head and a Glasgow Coma Scale of 14 or 15. Most, but not all studies, suggest that routine repeat x-ray computed tomography of the head is not needed unless the patient shows signs of clinical worsening. In the one study advocating for routine rescans, 5 patients, all with subdural hematomas, required interventions due to worsening scans despite no clinical worsening.

Injury Effects

Secondary Brain Injury

Secondary effects of a brain injury are those that follow from the body’s compensatory and reactionary mechanisms in response to the injury, both at the organ and cellular level. These effects can permanently damage the patient if not managed properly. They include cerebral swelling, brain tissue ischemia, excitotoxicity, oxidative stress and eventually apoptosis, also referred to as programmed cell death. Theoretically, these effects are both preventable and reversible.

Ischemia

Ischemia is defined as a period of time during which a tissue’s blood supply is temporarily stopped. Therefore, brain tissue ischemia is a period of time where the brain tissue lacks sufficient blood flow, which in turn prevents proper tissue oxygenation which is required for cells to remain alive and healthy. If this period of ischemia persists for too long, permanent brain damage may occur. Cerebral swelling, a cellular response to injury, increases intracranial pressure (ICP), which in turn leads to intracranial hypertension, the direct cause of the ischemia. Ischemic episodes in the brain can have very detrimental effects, with consequences that include cognitive damage and motor impairment.

Excitotoxicity

Excitotoxicity results from excessive release of excitatory neurotransmitters such as glutamate. Excitatory neurotransmitters increase cytosolic calcium ion (Ca2+) levels inside neurons, while inhibitory neurotransmitters maintain low cytosolic Ca2+ levels. When exposed to an abnormally high amount of excitatory neurotransmitter, a post-synaptic neuron becomes hyperactive. In a brain injury, the hyperactive neurons are those cells that have been injured. As Ca2+ is a potent modulator of many active processes, this high degree of activity will activate a higher than normal quantity of degradative enzymes, which will in turn mediate the apoptosis resulting from an excitotoxic condition.

Diagnosis

Imaging

X-ray computed tomography of the head should be considered, especially if the patient fulfills any criteria from the New Orleans Criteria clinical prediction rule:

"headache, vomiting, an age over 60 years, drug or alcohol intoxication, deficits in short-term memory, physical evidence of trauma above the clavicles, and seizure"

However, the Canadian CT Head Rule may have similar sensitivity but be more specific.

X-ray of the cervical spine should be considered, especially if the patient fulfills criteria from the Canadian C-Spine Rule clinical prediction rule for neck injury:

• Age 65 years or more
• Paresthesias in extremities
• Dangerous fall ("elevation >=3 ft or 5 stairs; an axial load to the head (e.g., diving); a motor vehicle collision at high speed (>100 km/hr) or with rollover or ejection; a collision involving a motorized recreational vehicle; or a bicycle collision")
• Inability to rotate the neck 45° to the right and left
  • Only test if "simple rear-end motor vehicle collision, sitting position in ED, ambulatory at any time since injury, delayed onset of neck pain, or absence of midline C-spine tenderness"
• Glasgow Coma Scale less than 15 (the Canadian C-Spine Rule was only designed for alert patients)

Biochemical Analyses

When patients enter the hospital with brain trauma, bodily fluids such as urine, cerebrospinal fluid (CSF), and blood are obtained in the assessment and treatment procedure. In many cases, these fluids are tested for certain chemicals that indicate the severity of injury.

Among the things tested for are cytokines, special proteins that are secreted by damaged cells and cells surrounding the injured site. These proteins participate in either a protective or damaging manner. Cytokines that result in neuroprotection will attenuate the body’s immune response against damaged cells, while cytokines that result in neurodegeneration will exacerbate or initiate the body’s immune response against damaged cells.

Interleukins (ILs) are a large class of proteins that participate in immune responses, both protectively and degeneratively. For example, IL-6 and nerve growth factor (NGF) respond neuroprotectively in a mutually dependent manner in response to brain injury , while IL-18 responds neurodegradatively in response to brain injury. </ref> Many other cytokines are synthesized in response to brain injury. Although the exact mechanisms of neuroprotection or neurodegradation resulting from the secretion of cytokines have yet to be entirely elucidated, the knowledge that these mechanisms exist is one of the first steps toward determining the most effective way to utilize this information in a clinical treatment context.

Another indicator of injury severity is if a change in the amount of oxidation that is occurring is detected. For example, lipid peroxidation is one form of oxidation that occurs at a higher rate in response to brain injury. Thiobarbituric acid reactive species (TBARS) are metabolic byproducts of the peroxidation of lipid membranes. Therefore, the amount of TBARS detected can be used to indicate if oxidation has indeed been occurring in response to a brain injury. However, one drawback to this method for detecting the quantity of oxidation that has been occurring is that actual brain tissue is required, meaning that this procedure can only be used in experimental investigations.

Treatment

Mild injury may not benefit from multidisciplinary or rehabilitation treatment. Some of the aspects of secondary injury currently have treatment strategies that can somewhat-effectively manage their consequences, but many of the current strategies for managing these effects do not always yield optimal results. Therefore, research is underway to better understand these mechanisms, as well as to find pharmacological treatments to prevent worsening of the damage of brain injury from preventable effects.

Management of Increased Intracranial Pressure

Increases in intracranial pressure result in brain tissue ischemia, which can cause permanent damage. One of the first steps to treating a brain injury is to reduce intracranial pressure if it increases. This can be managed through surgically draining CSF, as well as administering hypertonic saline (containing mannitol) which will function via the basic principles of osmosis to draw fluid from the swollen brain tissue into the circulatory system, thereby reducing the total volume of space occupied by the brain.

Management of Seizure Activity

Seizures can cause further damage to the brain. If antiseizure therapy is indicated, it should be started within the first 6 hours of injury, and should reach a therapeutic level within the first 24 hours of injury.

Management of Excitotoxicity

In many cases, patients are made mildly hypothermic. This slows the increase in excitatory amino acid levels that result in exitotoxicity, thereby attenuating the excitotoxic effects of secondary brain injury.

Management of Tissue Oxidation

Few treatments currently exist that allow for the management of the oxidation occurring during secondary brain injury. The hypothermia that is induced to slow the increase in levels of excitotoxic amino acids also functions to reduce the amount of oxidation that occurs. In the future, drugs that manage the oxidation occurring during the secondary phase of injury may become incorporated into treatment regimes. Some of the drugs that have been studied include Resveratrol and melatonin. Both of these drugs have been shown to prevent some of the oxidative damage that occurs during the secondary phase of injury.

Pediatric Considerations

Children are both physiologically and anatomically different than adults. Therefore, it is not surprising that their brains respond differently to a brain injury than do adult brains. Children’s brains are less able to compensate with increases in oxidation occurring within cells. The pediatric brain is also undergoing a significantly greater amount of synaptogenesis than is an adult brain, meaning that it is much less able to compensate for severed axonal connections than the adult brain.

Another aspect that is important to address with children is the causes of head injury, which tend to be either motor vehicle accidents and sports injuries, or for very young children, abuse, including shaken baby syndrome. In the year 2000, The prevalence of pediatric brain injuries resulting from trauma was 0.07% of children per year ≤ 17 years of age, an alarmingly high number that warrants more attention than it is currently receiving. Given this high number of injuries, and that a child’s brain in some cases requires different medical treatment than an adult brain, special considerations must be made when treating children for a brain injury.