Brain Swelling after Severe Brain Injury

Brain Swelling Creates Dangerous Increases in Intracranial Pressure

By Gordon S. Johnson, Jr.

Brain swelling after severe brain injury is a life threatening condition which can result in severe brain damage and disability. Brain surgery is often necessary and save lives.

Cortical Contusions

A contusion means a bruise. A cortical contusion means a bruise to the surface (the cerebral cortex) of the brain.  The problem with contusions (also called hematomas) is that bruises involve the collection of blood outside of blood vessels. Blood outside of blood vessels is toxic to brain tissue. A brain contusion also increases the amount of total fluid within the skull (brain swelling). As the skull is like a pressure cooker with a limited amount of storage volume, when there is an increase in the amount of fluid within the container, it increases pressure. Increases in ICP – intracranial pressure – are the main cause of secondary brain damage. Secondary brain damage is brain damage that occurs not at the time of the injury but over the hours and days after trauma. Secondary brain damage is the leading cause of delayed death after brain injury.

As pressure within the brain increases as a result of brain swelling, it becomes increasingly more difficult for blood to perfuse (flow) throughout the brain. The smallest of the vessels, called capillaries, are the blood vessels that provide the fuel and oxygen for the brain to work.

Think of brain activity as a fire occurring on the microscopic cellular level. This fire needs fuel for it to create the energy for the brain to work. The fuel is glucose (blood sugar). The fire also needs oxygen. Further, like if you had a fire going in your fireplace at home, the brain must find a way to exhaust the by-product of this energy reaction.  The failure to exhaust the waste products of this energy reaction becomes poisonous on the cellular level.  Absence of oxygen takes longer to cause brain damage than failing to vent the waste products from the brain. When the capillaries are compressed because of swelling or hematoma in the brain, brain cells die.

As ICP increases, progressively larger and more blood vessels will have blood flow reduced.  If the increase in pressure gets to the point that it compresses the brain stem, involuntary nervous system activities, such as heart beat and blood pressure, are interrupted. Brain stem compression often results in death.

Relieving the increase in intracranial pressure from hematoma is one of the primary purposes of brain surgery after severe brain injury.  Such surgery often involves removing a portion of the skull, so that the brain has room to expand and prevent secondary damage from an increase in ICP.  Such surgery is referred to as a craniotomy or a craniectomy.

Epidural hematoma

An epidural hematoma is a brain bruise that occurs between the dura and the skull. For more on the dura and other meninges, click here.

Subdural hematoma

Subdural hematoma is a brain bruise that occurs between the dura and the brain.

Midline Shift

The brain has two hemispheres, which are largely symmetrical.  In the normal brain a relatively straight line can be drawn between the right and left hemispheres, outlining the center of the brain. If brain swelling is occurring on one side of the brain but not the other, the swelling pushes that hemisphere across the center line.  When this happens it is called a “midline shift.”  Midline shift is one of the first clues of brain swelling on CT scan. Midline shift is particularly dangerous because it may also be accompanied by compression of the brain stem, which can cause death, as discussed above.