Brain Edema after Severe Brain Injury

Brain Edema, or Swelling, Causes a Harmful Rise in Intracranial Pressure

By Gordon S. Johnson, Jr.

Brain swelling, also known as brain edema, after severe brain injury is a potentially fatal state, causing severe brain damage and disability. Surgery on the brain is often necessary and can save lives.

Cortical Contusions

A cortical contusion means a bruise on the brain. (The cerebral cortex is the surface of the brain.)  The challenge with cortical contusions (also called hematomas) is that bruising creates a collection of blood outside of blood vessels, which is lethal to brain tissue. A cortical contusion also causes the amount of total fluid within the skull to rise, elavating intracranial pressure. Increases in intracranial pressure (ICP) are the major roots of secondary brain damage. Secondary brain damage occurs not in the first few moments after brain injury, but over the hours and days after the initial traumatic event. Secondary brain damage can cause death if the pressure is not controlled.

As pressure within the brain becomes greater in brain edema, it becomes more difficult for blood to perfuse (flow) throughout the brain. The tiniest of the vessels are the first to be closed off by this pressure, and it is those vessels that provide the fuel and oxygen for the brain to work.

Picture brain cells where there is a fire occurring on the cellular level. This cellular fire needs fuel in order to create the energy for the brain to function properly. The fuel would be glucose (blood sugar). The fire needs oxygen too. Furthermore, the brain must find a way to exhaust the by-product of this energy reaction.  The failure to remove the exhaust products of this energy reaction becomes lethal to the cell.  Absence of oxygen takes longer to cause brain damage than failing to vent the waste products. When the capillaries are compressed because of swelling, the fuel and oxygen can’t get to the cell and the exhaust can’t be removed. Without normal circulation, brain cells die.

As ICP increases, increasingly larger blood vessels will have blood flow decreased.  If the increase in pressure gets to the point that it compresses the brain stem, heart beat is interrupted, and blood pressure is unregulated. Brain stem compresses often results in death.

Lessening the rise in ICP from hematoma is a primary goal of brain surgery after severe brain injury.  Such surgery might involve removing a portion of the skull, so the brain has room to expand. This surgery will limit secondary damage from an increase in ICP.  These surgeries are called a craniotomy or a craniectomy. In a craniotomy, the bone flap is replaced at the end of the surgery. In a craniectomy, the bone flap is stored for months, giving the swelling more time to normalize.

Epidural hematoma

An epidural hematoma is a brain bruise between the dura and the skull. For more on the dura and other meninges (the protective coatings around the brain), click here.

Subdural hematoma

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

Midline Shift

The brain has two hemispheres. The hemispheres are largely symmetrical.  In the normal brain a line can be drawn between the right and left hemispheres. If brain swelling is occurring on only one side of the brain but not the other, the swelling drives that hemisphere across the center line, down the vertical center of the brain.  When this happens the diagnosis is a “midline shift.”  Midline shift can be seen on a CT scan. Midline shift is also of concern because it may be coupled with compression of the brain stem, which causes death, as discussed above.