In order to understand subarachnoid hemorrhages we have to first appreciate the "layers" of the brain and its surrounding structures.
The brain itself has three protective layers: dura, arachnoid, and pia.
The dura is a thick layer of fibrous tissue immediately next to the skull.
Below that is the arachnoid, which is a layer of delicate web-like tissue, hence the name "arachnoid.
" Finally, the layer closest to the brain is the pia.
The subarachnoid space, or the region between the arachnoid tissue and the pia contains cerebrospinal fluid, which acts like a liquid shock absorber for the brain.
Also contained within the subarachnoid space are blood vessels that penetrate down into the brain tissue.
Sometimes these blood vessels can leak; if this occurs there is said to be a "sub-arachnoid hemorrhage.
" Subarachnoid hemorrhages are usually caused by an aneurysm.
An aneurysm is an abnormal ballooning out of the blood vessel wall.
The balloon's dome is much weaker than the rest of the vessel wall.
These weak areas can rupture allowing blood to leak out of the vessel.
If this occurs in the brain the leaking blood flows into the subarachnoid space.
Other causes of subarachnoid hemorrhage include idiopathic (ie: unknown) causes, trauma to the head, arteriovenous malformations, vessel dissections, and very rarely tumors.
Regardless of the cause, blood will pool in the subarachnoid space leading.
The symptoms of the hemorrhage depend on how much blood has entered the subarachnoid space.
The most common presenting symptom is an intense headache; often described as "the worst headache of my life" by patients.
Accompanying the headache can be other neurological problems such as photophobia (ie: fear of light) and weakness.
If severe enough subarachnoid hemorrhage can cause coma and death.
Prompt diagnosis and treatment is necessary to prevent secondary complications.