Primary and Secondary Injury

The brain is about 3-4 pounds of extremely delicate tissue floating in fluid within the skull.

Under the skull, there are three membranes that cover and protect the brain. Brain tissue is soft, and can easily be compressed (squeezed), pulled, and stretched. When there is sudden movement of the head, a speeding up and and slowing down such as in a car crash or fall, the brain can move around violently inside the skull, resulting in injury. Bleeding can also occur, because the brain moves across sharp bony ridges inside the skull. When this happens, the swelling that is a normal result of injury increases pressure within the skull and can compress brain tissues and blood vessels, and can even cause a loss of oxygen.

The table below describes the primary and secondary causes of the brain injury. Primary injuries include the initial blow or insult itself, while secondary injuries are the body’s natural and continuous response to the injury, which can be just as devastating. Severe injuries can happen even without a lot of bleeding into the brain, when individual nerve cells are stretched and break (diffuse axonal injury), resulting in extensive injury to the entire brain.

Primary Injury

Traumatic Blow

  • Assault
  • Fall
  • Car accident
  • Blast waves from explosion

Penetrating Event

  • Gunshot wound
  • Stabbing

Cerebral Event

  • Stroke
  • Aneurysm
  • Anoxia
  • Brain Tumor

Secondary Injury


  • Increased intracranial (inside the head) pressure
  • Accumulation of blood (hematoma)
  • Excessive cerebrospinal fluid (hydrocephalus)


  • Slowly builds over time
  • Symptoms may not be recognized immediately (disorientation, headache, loss of consciousness)
  • Contusions or bruises can develop
  • Can reduce or completely halt oxygen to the brain (hypoxia; anoxia)