Types of Brain Injury

Primary brain injury refers to the sudden and profound injury to the brain that is considered to be more or less complete at the time of impact. This occurs at the time of the car accident, gunshot wound, or fall.

Secondary brain injury refers to the changes that evolve over a period of time (from hours to days) after the primary brain injury. It includes an entire cascade of cellular, chemical, tissue, or blood vessel changes in the brain that contribute to further destruction of brain tissue.

What are primary and secondary brain injury?

Primary brain injury refers to the sudden and profound injury to the brain that is considered to be more or less complete at the time of impact. This occurs at the time of the car accident, gunshot wound, or fall.

Secondary brain injury refers to the changes that evolve over a period of time (from hours to days) after the primary brain injury. It includes an entire cascade of cellular, chemical, tissue, or blood vessel changes in the brain that contribute to further destruction of brain tissue.

Brain injury may occur in one of two ways:

• Closed brain injury
  Closed brain injuries occur when there is a non-penetrating injury to the brain with no break in the skull. A closed brain injury is caused by a rapid forward or backward movement and shaking of the brain inside the bony skull that results in bruising and tearing of brain tissue and blood vessels. Closed brain injuries are usually caused by car accidents and falls. Shaking a baby can also result in this type of injury (called shaken baby syndrome).
• Penetrating brain injury
  Penetrating, or open head injuries occur when there is a break in the skull, such as when a bullet pierces the brain.

What is diffuse axonal injury (DAI)?

Diffuse axonal injury is the shearing (tearing) of the brain's long connecting nerve fibers (axons) that occurs when the brain is injured as it shifts and rotates inside the bony skull. DAI usually causes coma and injury to many different parts of the brain. The changes in the brain are often microscopic and may not visualize on computed tomography (CT scan) or magnetic resonance imaging (MRI) scans.