What is cerebral edema?
The medical term for swelling of the brain is cerebral edema. It occurs when the brain tissue swells due to an increase of fluid in the tissue spaces or within the cell itself. This leads to raised intracranial pressure as the brain enlarges to occupy more space than is available within the cranial cavity (skull cavity where the brain is housed). The pressure on the brain can cause a wide range of symptoms but initially and with moderate swelling, there may be no clear symptoms.This is also dependent on whether only certain parts of the brain are swollen (localized edema) or if the swelling is throughout the brain.
Types of Brain Edema
There are two main types of brain swelling :
- Cytotoxic, where there is an increase in intracellular fluid (fluid within the cell) of the brain tissue.
- Vasogenic, where there is an increase in the intercellular fluid (fluid around the cells in the tissue spaces – interstitial fluid).
Cytotoxic edema arises when there is damage to the cell membrane (neuron) which disturbs the regulation of the fluid within the cell. This is seen in cases like oxygen deprivation (hypoxia), inadequate blood supply (ischemia) or metabolic damage. Vasogenic edema occurs where there is damage to the blood vessel(s) in the brain allowing fluid to leak from the intravascular compartment into the brain tissue. This may be seen with vasculitis, inflammation, infection or generalized swelling of the body (anasarca).
Two other less common types of edema may lead to increases in the intercellular (interstitial) fluid like with vasogenic edema but for different reasons. Osmotic edema may occur when the osmotic balance that maintains the fluid difference between the fluid in the blood vessels and the tissue spaces is disturbed thereby allow fluid from the blood to move across into the tissue spaces. This may be seen with water retention or certain endocrine disorders involving ADH (antidiuretic hormone). In hydrostatic edema, high blood pressure forces fluid out of the blood vessel and into the tissue spaces.
What happens in brain swelling?
Most acute causes of cerebral edema cause rapid swelling of the brain. This is more dangerous because with gradual swelling the body has time to compensate through various mechanisms like altering the volume of CSF (cerebrospinal fluid). As the brain tissue swells, various changes occur – the convolutions of the brain surface become flattened and the cavities of the cerebral ventricles are compressed. The outward pressure of the swollen brain opposes the inward pressure of the cranium and surrounding cerebrospinal fluid. This leads to brain herniation where there is disruption of the blood supply to the brain (ischemia, hemorrhage), compression of the cranial nerves and even the brain stem. Death of brain cells can cause a range of symptoms, lead to permanent damage and even to death.