Subarachnoid hemorrhage

There are two main types of stroke: a hemorrhagic stroke, which occurs when an artery ruptures and bleeds within the brain, and an ischemic stroke, which occurs when an artery gets blocked.

Hemorrhagic strokes can be further split into two types, an intracerebral hemorrhage which is when bleeding occurs within the cerebrum, and a subarachnoid hemorrhage which is when bleeding occurs between the pia mater and arachnoid mater of the meninges - the inner and middle layers that wrap around the brain.

We’ll focus on subarachnoid hemorrhage, which can quickly lead to death if they’re left untreated.

Subarachnoid hemorrhages can lead to a pool of blood under the arachnoid mater that increases the intracranial pressure and prevents more blood from flowing into the brain.

Ok - let’s start with three protective layers of the brain called meninges.

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.

Between the arachnoid mater and the pia mater is the subarachnoid space, which houses 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.

This space is also where the arteries that supplies the brain travel, and it is the location of the blood brain barrier where CSF and the vascular system can exchange nutrients.

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.