Coma (cont.)
Epidural, subdural, and subarachnoid hemorrhages
The lining of the brain has multiple layers, and these layers can act as potential
spaces where bleeding can occur. Epidural (epi= outside the dura= an outer layer
of brain lining) and subdural (sub=below the dura) may not cause coma
immediately, but as the bleeding continues, it compresses the injured side of the
brain and shifts it to the unaffected side. Now both cerebral hemispheres are
affected and loss of consciousness or coma may occur; the more swelling, the
deeper the coma.
Subarachnoid hemorrhage (below the arachnoid layer) is in the layer of the
brain lining where cerebrospinal fluid (CSF) is. CSF is the nutrient fluid that
bathes the brain and spinal cord. Bleeding here may be without symptoms or it
may cause significant problems, such as paralysis.
Bleeding can occur within the skull or brain without trauma. Blood
accumulating in areas it should not b,e result with the same problem.
Some medical causes include:
- Hypertension (high blood pressure):
when blood pressure is too high, and not controlled, blood
vessels in the brain may not be able to tolerate the high pressure and may leak
blood.
- Cerebral aneurysm, or an area in a blood vessel that is congenitally weak and
ruptures. Some people are born with blood vessels that have a weak wall and it
gradually balloons, like a weak spot in an inner tube. At some time in their
life, or perhaps never, the weak spot gives way and blood is spilled into the
brain.
- Arteriovenous malformations (AVMs) are abnormal blood vessels where arteries connect to veins and cause potential weak spots that can leak blood. Normally, arteries branch into smaller and smaller vessels until they form the smallest set of vessels called capillaries.
Capillaries form meshes where chemicals, nutrients, oxygen and carbon dioxide are exchanged from the blood stream to individual cells. The capillaries then merge to form larger blood vessels, the veins. In AVMs, this relationship of artery to capillary to vein is abnormal.
- Tumors, either benign or malignant, can be very vascular (composed of many
veins and capillaries) and have significant bleeding potential.
Picture of the brain and potentially brain injury areas
Next: Swelling »
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