The brain is injured when a force impacts the head. As explained by the Brain Injury Association of Utah (BIAU), when external force injures the brain it is referred to as traumatic brain injury, whereas acquired brain injury is when an internal event or force injures the brain. Traumatic injury is further divided by levels (mild to severe) and there are various types of acquired injury. However, any brain injury can be serious, with symptoms including numbness and weakness in the extremities, extreme drowsiness, headache, dizziness, vision problems, slurred speech, vomiting or nausea, loss of consciousness and cognitive issues.
Types of Acquired Brain Injury
Acquired brain injuries are generally divided into two types: anoxic and hypoxic. Both types of injury involve a lack of oxygen to the brain. In hypoxia, the brain gets some oxygen, but not enough, due to limited blood flow or blood pressure in the cerebral vessels. This condition is also called ischemia, stroke, or stagnant hypoxic injury. In anoxia, the brain receives no oxygen for one of several reasons:
anoxia - no oxygen due to a lack of oxygen being breathed in
anemia- blood reaches the brain but is not carrying oxygen
toxic injury-toxins or metabolites blocks the use of oxygen from the blood
stagnant-blockage of blood vessels (overlaps with hypoxic injury).
Causes of acquired brain injury include high altitude sickness, drowning, cardiac arrest and heart arrhythmias, respiratory distress and disease, carbon monoxide poisoning, suffocation, choking, brain tumors, blood clots and toxins/poisoning.
A third type of acquired injury overlaps with traumatic injury – hemorrhage. An aneurysm (ruptured blood vessel) that leads to bleeding within the brain or brain cavity can increase pressure within the cavity and injure the brain via anoxia/hypoxia or physical distress. However, hemorrhage can also occur due to trauma and is usually discussed in that context. causes of traumatic brain injury (TBI) are falls, motor vehicle accidents, assaults and collision with a moving object. The types of TBI are generally considered as closed and open injuries. Open injuries are penetrating injuries, with an object penetrating into the brain cavity.
Closed injuries include concussion, contusion, coup-contrecoup, and diffuse axonal injury. The BIAU considers concussion the most common type of TBI. Concussions are due to fast movement of the brain within the cavity, such as the result of shaking, whiplash, or direct blows, and can result in coinciding injuries such as nerve or blood vessel damage. Contusion is a bruising of the brain due to bleeds from small blood vessels after a direct blow or fast movement. Coup-contrecoup is a type of double contusion, where the brain is bruised both at the site of impact within the skull and on the opposite side due to the reaction force that slams the brain back into position. Diffuse axonal injury occurs with rotational forces, as seen in shaken baby syndrome, and results in torn nerve tissue around the brain.
Levels of Brain Injury
The BIAU considers three levels of brain injury: mild traumatic, moderate traumatic and severe brain injury. The level is determined by the Glasgow coma score.
Most brain injuries are mild or moderate in nature. Mild injury is generally a concussion, with limited altered cognitive state or consciousness. Moderate injury is caused by non-penetrating head trauma or violent shaking. Loss of consciousness is common with potential for lifelong cognitive, physical or behavioral disability. Severe brain injuries are caused by penetrating trauma, acquired brain injury, and severe closed head injuries such as coup-contrecoup and diffuse axonal injury. Hemorrhage is often seen with severe brain injury.
The Brain Injury Association of America has more information about recurrent TBI and secondary brain injury syndromes. The BIAA also offers support and educational materials for survivors of brain injury and their families.