Swelling of the Brain

Brain edema is usually vasogenic or cytotoxic

When fluid collects between cells and causes swelling, this is called edema. In head trauma, edema is a process that develops because the blood vessels and tissues of the brain have been damaged either through penetration, crushing or tearing.

Edema is dangerous, because it increases pressure inside the skull. This in turn pushes down on brain tissue reducing blood flow and oxygenation. Edema also changes the immediate environment surrounding the nerve cells of the brain, which affects their ability communicate and survive.

When brain cells lose their protected environment and are unable to communicate with other nerve cells, there can be drastic changes in the entire body. These may include confusion, loss of consciousness, changes in heart rate, breathing, blood pressure, and alterations in one’s ability to move. 

There are two common types of brain edema after traumatic brain injury: Vasogenic and Cytotoxic

Vasogenic Brain Edema

Vasogenic edema develops when the blood brain barrier (BBB) is damaged. The blood brain barrier protects the brain by preventing excess fluid, hormones, neurochemicals, toxins, viruses and bacteria from entering into the brain, and altering how nerve cells function. When the barrier is broken, fluid leaks into the brain and surrounds the nerve cells. As more fluid leaks into the brain, pressure inside the brain goes up.

The blood brain barrier is made of microscopic cells called endothelial cells, which line the smallest blood vessels inside the brain.

This makes it impossible to go in and manually fix the barrier. Luckily, the body’s natural inclination is to heal itself, so as soon as the barrier is broken, cells begin the repair process.

It’s estimated that BBB is at its widest open to unwanted fluids and materials about 4-6 hours after an injury, and then it slowly repairs itself over the next 7 days.

One of the key problems is that an excess of fluid and other materials around the nerve cells in the brain contributes to further brain cell damage. Brain cells that were not directly harmed during the initial trauma, have difficulty surviving without the right balance of sugar, amino acids and other compounds essential for cellular function, and they begin to die.

As they die, they spill their intracellular contents into the surrounding space, and this contributes to cytotoxic edema.

Cytotoxic Edema

Cytotoxic edema occurs when nerve cells are directly injured during head trauma, or if the environment surrounding the cells becomes imbalanced. Vasogenic edema is one cause of an imbalanced environment that contributes to cytotoxic edema.

When there is excess fluid in the brain, nerve cells start to absorb that fluid. As water flows into a nerve cell, it overfills, becomes distended and ruptures.

A nerve cell contains a large store of neurochemicals which it uses to communicate with other nerve cells.

In tiny quantities these chemicals are safe, and serve their function effectively. However, in large quantities they are toxic.

When the nerve cell ruptures, it causes neurotransmitter chemicals, such as glutamate, to spill into the surrounding environment. As more and more cells die, greater amounts of neurochemicals are released into the environment between the nerve cells. This causes the environment to become very toxic, which in turn leaders to further cell death.

It is a cycle that is difficult to stop once it has started and it often continues even after the blood brain barrier has healed itself.

Sources:

Donkin, J. and Vink, R. (2010) Mechanisms of cerebral edema in traumatic brain injury: therapeutic developments. Current Opinion in Neurology; 23(3):293-9. DOI: 10.1097/WCO.0b013e328337f451

Shotaro, M., & Yutaka, K. (2015). Pathogenesis of Brain Edema and Investigation into Anti-Edema Drugs. International Journal Of Molecular Sciences, 16(5), 9949-9975. doi:10.3390/ijms16059949

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