Brain herniation

Brain herniation is what it’s called when some brain tissue moves outside of the skull, or moves across or into a structure with the skull.

Brain herniation typically happens in response to increased intracranial pressure, which refers to a high pressure within the skull.

An intracranial pressure above 15 mmHg is considered high.

OK - let’s start with some basic brain anatomy. The brain has a few regions - the most obvious is the cerebrum, which is divided into two cerebral hemispheres, each of which has a cortex - an outer region - divided into four lobes including the frontal lobe, parietal lobe, temporal lobe, and the occipital lobe.

There are also a number of additional structures - including the cerebellum, which is down below, as well as the brainstem which connects to the spinal cord.

Now zooming in, the brain and spinal cord is covered by the meninges, which are three protective layers of the brain.

The inner layer of the meninges is the pia mater, the middle layer is the arachnoid mater, and the outer layer is the dura mater.

These first two, the pia and arachnoid maters, form the subarachnoid space, which houses the cerebrospinal fluid, or CSF.

CSF is a clear, watery liquid which is pumped around the spinal cord and brain, cushioning them from impact and bathing them in nutrients.

The outer membrane is the dura mater, which forms the meningeal folds, such as falx cerebri and tentorium.