Brain herniation

Alternative names:

cerebellar herniation; herniation of the brain; herniation syndrome; transtentorial herniation; uncal herniation

Definition:

A condition in which a portion of the brain is displaced because of increased pressure inside the skull, resulting in progressive damage to brain tissue that may include life-threatening damage to the brainstem.

Causes, incidence, and risk factors:

Brain herniation occurs when pressure inside the skull (intracranial pressure) increases, and displaces the brain tissues. This is commonly the result of brain swelling (cerebral edema) from a head injury, or may be the result of space-occupying lesions such as primary brain tumor, metastatic brain tumor, or other lesions within the brain. Brain herniation may also occur with bacterial meningitis.

The most common type of brain herniation occurs when a portion of the temporal lobe is displaced (uncal herniation), which compresses cranial nerve III, the midbrain, and the posterior cerebral artery, leading to coma and respiratory arrest (breathing stops).

Another critical type of brain herniation occurs when part of the cerebellum is displaced through the foramen magnum (the area where the spine joins the skull). This compresses the brainstem and causes death from lack of breathing (the respiratory center in the brain stem is destroyed) and circulation. Other areas of the brain may be herniated, but they occur much more rarely than uncal herniation or foramen magnum herniation.