Even though the skull and cerebrospinal fluid surround the brain for protection, it remains fragile and susceptible to injuries.

Brainline.org explains that the type of traumatic brain injury typically has a strong influence on how a person may recover.

Penetrating primary injury

Between 1% and 2% of traumatic brain injuries involve an object that penetrates the outer layer of the membrane that lines the skull. This could be a fragment of metal in a car crash, a bullet or a piece of the skull, for example.

Closed primary injury

There are four basic types of primary injuries.

  1. Intracranial hematoma: A blood vessel rips or tears and leaks blood into the tissues or spaces surrounding the brain. The hematoma could form a clot under the skull but outside the membrane around the brain or between the brain and the membrane. The injury could also involve hemorrhaging between the layers of the membrane or into the ventricles of the brain.
  2. Skull fractures: If the break is a crack or thin line, it may heal on its own, but if the break goes inward or crushes a portion of the skull, it may require surgery to correct. If the fracture happens at the brain’s base, the cerebrospinal fluid may leak.
  3. Contusions/coup-contrecoup: When the brain strikes the inside of the skull, it causes bruises (contusions) to the tissues. Typically, this is a coup-contrecoup injury because after the brain hits in one location, it then slides back and strikes the opposite wall of the skull, creating injuries in at least two places.
  4. Diffuse axonal injury: Rotational force can cause the connections between brain cells to twist and tear.

Secondary injury

The initial impact may trigger secondary events that cause further injuries. These may include oxygen deprivation, reduced blood flow or fluid buildup around the brain.

Second impact syndrome is a rare secondary injury type. According to the Mayo Clinic, a TBI changes the brain chemical levels, and if the brain sustains a second injury before the first has healed, it could cause rapid swelling that is often fatal.