A brain herniation occurs when a part of the brain pushes downward inside the skull through the opening that leads into the neck.

What is going on in the body?

The brain is supported within the skull by a horseshoe-shaped piece called the tentorium. There is an opening in the tentorium where the brainstem connects to the brain. This is where most herniations occur.

Conditions that cause swelling in the brain or increased pressure in the skull can cause brain tissue to be pushed into this opening. This is called a herniation. For instance, if there is a mass, such as a tumor, in the head, the brain will swell. Since the skull is rigid, swelling will force the brain into the area of least resistance. This would be the hole in the center of the tentorium. The swelling may result in the brain shifting from its usual position to an abnormal position in the skull.

What are the causes and risks of the condition?

Anything that causes swelling in the brain might lead to herniation. Some common causes include:

Brain herniation can cause severe brain damage or even death. The brain tissue that is being squeezed through the opening and the brainstem tissue can be permanently damaged. The ability to breathe, keep the heart beating, be alert, and think can all be damaged.