Here are some terms that describe the various ways brain cells are injured.

Concussion—happens when a blow or jolt to the head causes your brain to bounce against the inner walls of your skull.  This causes temporary changes that interfere with the brain’s functioning.  These changes lead to chemical imbalances inside the brain cells and also may reduce blood flow to the brain.  Basically, a concussion doesn’t usually kill brain cells, but instead makes them sick and temporarily malfunctioning.

The main symptoms at the time of a concussion are headaches and amnesia surrounding the event.  Most of the time people do not lose consciousness, but they may not be able to remember the concussion happening.  I’ve treated football and soccer players who have received concussions during a sporting event who were unable to remember even playing a game that day.  They were never knocked out and some of them even stayed in the game!

Next, symptoms such as memory problems, confusion, crankiness, inability to control emotions, and loss of interest may appear.  Concussion symptoms are not life threatening and they usually subside on their own in several weeks.  Occasionally they may continue on for several months in what’s called a post-concussive syndrome. 

More than a million concussions occur in this country each year.  “Concussion” is an older term and today “minor head trauma” or “mild traumatic brain injury (MTBI) are more correct terms.  These are often used interchangeably.

Contusion—bruising of brain tissue.  This happens when small vessels are injured and leak blood into brain tissue.  These primarily occur in areas of the brain located near sharp ridges on the inside of the skull.  Many people are surprised to find out that the inside of the skull is quite different from the smooth outside.  The inner skull contains cavities and sharp bony ridges, which play a significant role in brain injury.  Contusions usually heal on their own without medical intervention.  However, there is the chance of edema (brain swelling) which can increase the pressure inside the skull and possible lead to a coma.

Intracranial hemorrhage—bleeding within the skull.   This occurs when a blood vessel in the head is ruptured (a much bigger blood vessel than a contusion).  These are serious medical emergencies as the buildup of blood within the skull can increase the internal pressure, which can lead to a coma or death.  Intracranial hemorrhages can be caused by trauma or non-traumatic causes such as strokes or aneurysms.  Taking blood thinners increases the risk of brain hemorrhaging.

Diffuse Axonal Injury—one of the most devastating types of brain injury, which occurs in about one-half of all brain injuries.  Damage is caused when axons are stretched and torn.  This results when the head is rapidly accelerated or decelerated (motor vehicle accidents, shaken baby syndrome).  It rarely kills a person, but is a frequent cause of coma or a persistive vegetative state.  The frontal and temporal lobes are the most likely parts of the brain to sustain this type of injury.

Diffuse axonal injury has two parts: a primary injury—the initial axon damage resulting directly from the force—and then the secondary injury—a poorly understood process where stretched axon initially survive the trauma, but then biochemical changes occur inside the neuron and it dies over the next several days.

Anoxic Injury—Brain cells are damaged from a partial (hypoxic) or a complete (anoxic) lack of oxygen.  Brain cells without oxygen start to die in only a few minutes.  In fact, unconsciousness can occur in 15 seconds and irreversible brain damage in 5 minutes of oxygen deprivation.  Serious brain injury can happen from kids using the “sleeper hold” in wrestling on each other.  Newborns are also vulnerable to anoxic injuries.

There are 3 types of anoxic injuries:

•    Anoxic anoxia—no oxygen from the lack of blood flow.  The most common causes are heart attacks, strokes, and injuries with substantial blood loss
•    Anemic anoxia—the blood doesn’t carry enough oxygen.  Can happen from severe anemia, carbon monoxide poisoning, drowning, asphyxia, and suicide attempts.
•    Toxic anoxia—toxins block oxygen in the blood from being used.  The most common causes are infections and encephalitis.

The frontal lobe is the most vulnerable area of the brain to anoxia or hypoxia. 

Coup-Contrecoup—this results in two injuries occur from one blow.  The coup injury occurs under the site of impact.  The contrecoup injury occurs on the side opposite the area that was impacted.  This is caused by the brain bouncing back and forth against the skull.  Vehicle accidents frequently cause coup-contrecoup injuries.  You can also sustain a coup-contrecoup injury without direct impact to the head, such as with a whiplash or shaken baby syndrome.

Penetrating Brain Injury—A tearing of the brain from a skull fracture or gunshot wound.  Causes large vessels to rupture and bleed into the brain and the space between the brain and skull.  These types of injuries also allow bacteria into the brain, which can lead to infections such as encephalitis and meningitis.