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Ways the Brain is Injured

In the United States traumatic brain injury (TBI) is a leading cause of death for persons under age 45. TBI occurs every 15 seconds. Approximately 5 million Americans currently suffer some form of TBI disability. The leading causes of TBI are motorvehicle accidents, falls, and sports injuries. While the brain is by far the most complex object on earth, it is soft and vulnerable with a consistency of firm pudding.

Coup and Contrecoup
Coup - Contrecoup Injury
Two image illustration showing coup caused by the primary impact
and the secondary impact or contrecoup injury.

A concussion is a sudden trauma-induced alteration of the alert state. The person may be unable to concentrate or be confused for a few seconds, or completely lose consciousness and fall down. The brain is capable of recovering from a concussion. How much force is necessary to cause permanent brain damage is under study, and hence still unclear. Over the years, professional boxers suffer permanent brain damage. The force of a professional boxer's fist is equivalent to being hit with a 13 pound bowling ball traveling 20 miles per hour, about 52 g's. Plopping down into an easy chair can generate up to 10 g's. So, it seems that somewhere between 10 and 50 g's is the threshold to permanent brain injury. This does not mean that accelerations over 50 g's have to cause permanent brain damage. Football players are subjected to 200 g's, and Indy race car drivers have been subjected to 80 g's without permanent injury, but they were wearing helmets.

Football players and race car drivers also protect their heads from being whiplashed. Whiplash seems to be particularly damaging to the brain. Woodpeckers smack their heads against trees with 1200 g's of force without suffering brain damage. Part of the reason is that they keep their heads in the plane of their body; the head does not rotate in a "yes-no" manner during the pecking. If there were some way to stabilize the head when driving - akin to wearing a mail suit from the Middle Ages - more people would walk away from automobile accidents without serious brain injury.

The brain is vulnerable to traumatic damage in two ways. The cerebral cortex can become bruised - contused - when the head strikes a hard object (or a hard objects strikes the head). Or, the deep white matter can suffer diffuse axonal injury when the head is whiplashed without hitting a hard object (or being hit by one). In serious whiplash injuries, the axons are stretched so much that they are damaged.

Cerebral contusions tend to occur at the tips of the frontal and temporal lobes where they bang up against the interior of the skull. Diffuse axonal injury occurs more toward the center of the brain where axons are subjected to maximal stretching.

Direct Trauma

Any force that penetrates or fractures the skull may cause severe brain injury as destructive shock waves are sent through the brain matter. Displaced fractures of the skull can also push bone into the brain, causing tissue damage.

Direct trauma to the brain can occur when the skull strikes, for example, the floor in a fall accident or strikes a steering wheel in a car accident. Although the skull may not be penetrated or fractured in these types of accidents, the forces imparted to the brain can cause the brain to collide against the inside of the hard skull. When a moving head comes to a quick stop, the brain continues in its movement, striking the interior of the skull. This can cause bruising of the brain (a contusion) and bleeding (hemorrhage). Injury in these types of accidents occurs in parts of the brain closest to the point of impact, quite often the tips of the frontal and temporal lobes. In cases of blunt head trauma the brain can also be injured directly opposite the site of trauma -- on the other side of the brain, an injury known as contrecoup. This injury typically occurs when a moving head strikes a stationary object like the windshield. At impact the brain opposite the site of impact is pulled away from the skull, injuring the brain there.

Indirect Trauma

Medical research has discovered another mechanism of brain injury besides direct blunt trauma to the skull. The well-known phenomenon of the Shaken Baby Syndrome is an example. Severe shaking greatly stretches and damages delicate nerve cells, at times causing very significant injury or even death. In adults, severe whiplash can involve severe forces that may shake or rotate the brain enough to cause permanent brain damage.

Diffuse Axonal Injury

We hear a lot about "brain matter" and "white matter" in the brain. If the brain was a grapefruit, the gray matter would be found in the skin of the grapefruit. The white matter, if you could imagine very thin spaghetti strands, connect the different lobes of the brain and allow the brain to communicate with other parts of the brain. The white matter is composed of long nerve fibers called axons, which are each coated in a fatty molecule which works like insulation. The axons carry electrical signals to other parts of the brain very rapidly.

In ancient history, humans could not very likely suffer enough trauma to commonly effect the white matter of the brain short of falling off of a cliff. However, now that we have high rise buildings and rapidly moving vehicles weighing several tons, we now have forces sufficient to do that. Because of this, the science around "diffuse axonal injury" has had to evolve.

When forces are imparted to the head and neck, especially rotational forces, the brain tissue itself becomes distorted, twisted and injured. Because this happens not in one area of the brain (known as a "focal injury") but in a widespread manner. This stretching can injury the axons, especially at the point where the white matter connects with the gray matter, an area known as the "gray/white junction."

Until recently, it was more difficult to visualize white matter damage on MRI than to visualize damage to gray matter. However, the recent advent of DTI/MRI (Diffusion Tensor Imaging) allows doctors to more accurately determine whether white matter has been damaged in a trauma or not.

Because of these breakthroughs, we now know that diffuse axonal injury (DAI) is the leading cause or method of brain injury in the world. The earlier medical consensus was that DAI only was seen in persons with a severe brain injury, who would have been in a coma for some time. However, now that DTI and other more delicate instruments have been developed to look more finely at the brain after injury, we know that DAI occurs in all types of brain injury, from mild to moderate to severe. Remember, though - a CT scan, a normal MRI, or x-ray will not pick up diffuse axonal injury in the white matter, only DTI. Remember to ask your doctor about that.

Lateral views showing motion of head and neck during whiplash injury.

A second method of how the brain can be injured in high speed velocity change scenarios (a fall from a great height, high speed car accident) is called "Isotropic Stress." Whereas diffuse axonal injury involves the deforming or stretching of the brain tissue, resulting in tearing, isotropic stress causes damage through a "pulse" or "pressure wave" that moves through the brain at extraordinarily high speeds. The damage is caused by a sudden change in the density of the inside of an individual brain cell. The instant compression causes damage to the internal structures of the brain cells.

The fact that there is confusion in the medical world about DAI should not be surprising, since the concept was not even found in neurological textbooks as late as 1985. Because of this, older physicians tend to believe that if someone is walking and talking, there must not be any organic brain injury, and that if there are continued complaints, that they are "psychological." This type of horrible treatment of the brain injured was common in the past, but due to a large part of our returning Iraq and Afghanistan veterans, the medical world and the world at large are now coming to grips with the horrors of mild and moderate brain injury.

Secondary Cellular Brain Injury (Post Traumatic)

It was once thought that the damage to the brain during an accident or explosion happened only at the time of the traumatic event and that thereafter, healing proceeded. Unfortunately, we now know that is not the case.

For the past 20 or 30 years it has become more and more well known that an injury or trauma to the brain sets in motion molecular and hormonal changes in the brain in reaction to trauma. Unfortunately, many of these chemical reactions are destructive to the brain and cause continuing brain injury for weeks and years following the traumatic event. How does this happen?

The brain has it's own system of dealing with foreign materials, viruses, or trauma. The rest of the body depends largely on white blood cells or T-cells attacking invaders and making repairs. However, in the brain, this function has taken over by structures in the brain called "glial cells or astrocyctes." When these cells become activated by trauma, they tend to remain activated for years, during which they attack healthy or repairing brain cells. In response to trauma, the brain cells produce too much calcium and that becomes toxic to areas of the brain. The delicate balance of different organic molecules crucial to brain function becomes disruptive after trauma and recent studies have suggested that this imbalance continues for at least eighteen years in brain injured patients. Some of these imbalances can be noted on a type of MRI called spectroscopy.

The bottom line is that people can and do get worse in the short run with brain injury. Part of this is due to gradually getting back to "real life," rather than lying on a couch taking medication. Some of it is due to the slow secondary damage to the brain.

Injury by Lack of Oxygen

Our brains use a great deal of our body's oxygen and if the brain is starved of oxygen, that condition is known as anoxia. Anoxia can occur during drowning incidents, a heart attack where breathing has stopped and there is no CPR, or in other circumstances. If oxygen is not obtained within eight minutes, it is likely there will be permanent damage to the brain. From ten to twelve minutes, it is likely that some severe damage will be suffered.

Hypoxia, on the other hand, is the condition of having a decreased and insufficient amount of oxygen for a period of time, again this could happen during a heart attack, or from exposure to something like carbon monoxide. Damage from hypoxia is often seen in the hippocampus, the area of the brain that creates memories. Some toxic chemicals can attach onto the body's oxygen and cause brain damage from lack of oxygen, depending on the duration of the exposure and the level of chemical one is exposed to. This combination is called "the dose."

Secondary Types of Brain Injury

In addition to direct neural damage discussed above, injury to the brain can also result as a secondary phenomenon following injury to nonneurologic structures.

Edema - is a swelling of the brain. Swelling of the brain becomes dangerous when the swelling causes a rise in intracranial pressure which prevents blood from entering the skull to deliver glucose and oxygen to the brain. Sustained high intracranial pressure can be relieved through medication, or in more severe cases, by placing a hole in the skull to drain off some of the high-pressure cerebrospinal fluid.

Hematoma - is a collection of blood due to tissue injury or the tearing of a blood vessel. CT scans done at the hospital are particularly effective in detecting brain bleeds. Bleeding into the brain after trauma can occur days after the patient is released from the emergency room. The dura is a tough membrane that covers the entire brain and spinal cord. A blood clot that develops outside the dura, between the skull and dura, is known as an epidural hematoma. A blood clot that develops between the dura and the brain is called a subdural hematoma. Gently resting against the brain itself is a thin, delicate membrane called the arachnoid. Underneath the arachnoid, between the arachnoid and the brain itself, is cerebrospinal fluid bathing and circulating around the brain. Blood leaking into the cerebrospinal fluid is known as a sub-arachnoid hemorrhage.

Hydrocephalus and Hygroma - are collections of fluid in and around the brain. The brain is hollow; the interior cavities, called ventricles, contain cerebrospinal fluid circulating from the ventricles up over the surface of the brain where the cerebrospinal fluid is absorbed. If blood somehow gets into the cerebrospinal fluid and blocks the spinal fluid absorption sites, spinal fluid will back up into the ventricles, enlarging them - a condition called hydrocephalus. If the pressure inside the ventricles becomes excessive (risking damage to the brain), a tube may need to be inserted into the ventricles to relieve the pressure. A hygroma is a localized fluid buildup usually in the subdural space. Again, if pressure in the hygroma presses against the brain, surgery may be necessary to relieve the pressure.

Intracerebral hemorrhage
Coronal section through the skull reveals a intracerebral hemorrhage. The central large dark area represents the hemorrhage. Note the midline shift.
Epidural hematoma
Coronal section through the skull and brain reveals a epidural hematoma. The dark area in the lower left area is the hematoma. Note the broken blood vessel and the shift of midline structures.

Subdural hematoma
Coronal section through the skull and brain
reveals a subdural hematoma. The dark area in
the upper left area is the hematoma.


The single most important criteria, historically, to determine whether or not brain injury was likely to occur, was the notion of loss of consciousness (LOC). In the past twenty years researchers have come to the consensus that an actual LOC is not required in an accident for brain injury to occur. For example, I have had a client who was shot in the head through the middle of ~ by a 22 caliber bullet. It went all the way through his brain. The CDC now defines the requirement as being an "alteration in consciousness," meaning that while someone might not be "out," they are awake but confused, awake but dazed, awake but not completely themselves.

Were you Knocked Out - unfortunately, it is difficult for a person who is alone to determine whether they have lost consciousness or not. There is no appreciation for the "lost time" only, in some cases, an identification that time was lost. (I remember the bang from the accident and the next thing I remember a policeman was knocking on the window, would be an example). If someone does not see the unconscious person and later reports that to EMTs or the emergency room personnel, all in the hustle and confusion of an accident scene, that information may get lost. Most insurance companies will be reluctant to pay money or believe brain injury has occurred if there has not been a documented loss of consciousness. This "requirement' is rather silly in that many factors are present that make that determination difficult.

Post Traumatic Amnesia (PTA) - loss of memory for events prior to the injury (retrograde amnesia) and events following the injury (anterograde amnesia) frequently occur after head injury. In general, a patient with longer periods of post traumatic amnesia tends to have more of a severe injury. Studies have shown that individuals are not good at estimating their own length of amnesia (Gronwall 1980). Therefore, family members should make note of any anterograde or retrograde amnesia and track its improvement.

Concussion - a concussion is an alteration of conscious awareness after head trauma. The collection of symptoms following a concussion is called the postconcussion syndrome (PCS), and include dizziness, nausea, vomiting, headache, disorientation, forgetfulness, irritability, depression, mood swings, insomnia, and loss of libido. Most cases of PCS resolve after a few months, but approximately 20% of cases can involve longer term problems.

Encephalopathy - a disturbance of brain function indicating something is wrong with both sides of the brain's gray matter. Signs of encephalopathy include stupor, confusion, memory loss, inattention, agitation, and inappropriate aggression. An encephalopathy after head trauma only means the brain is not functioning properly. It does not necessarily mean the dysfunction is permanent.

Focal Neurologic Signs - signs that allow a doctor to conclude that a specific part of the brain is not functioning.

Seizure - nerve cells communicate with one another electrically and chemically. One nerve sends an electrical discharge along its axon to stimulate another distant nerve. The actually stimulation is done chemically. When the electrical discharge reaches the end of the axon, the electricity causes the axonal tip to spit a chemical "neurotransmitter" at receptor sites on the next nerve cell. All this takes place in a nice orderly fashion. A "grand mal" seizure occurs when every nerve cell in the brain rapidly fires electrical discharges at one another. The resulting chaos causes the patient to lose consciousness, fall down, and convulse. The same uncontrolled discharges in a focal area of the brain may cause the patient to experience or do what function that focal area normally controls. Such "focal" or "partial" seizures may manifest as recurrent bouts of numbness, fear, anxiety, a forced memory, jerking of a limb or face, lip smacking, sudden staring spells, or inability to speak.

PERL - medical personnel commonly test an individual with a head injury to see if the Pupils are Equal and Reactive to Light (PERL). Unequal pupils or unreactive pupils in a comatose patient after a head injury can signify a dangerous rise in intracranial pressure due to swelling, hematoma, hydrocephalus, etc. Urgent lifesaving surgery is often necessary to relieve the elevated pressure.


There has been a hypothesis that a person struck in the head who suffers facial fractures may have decreased injury to the brain because of the fracture being a "shock absorber" to the brain. However, a recent study (Martin R.C. 2002) showed that the outcome of those with facial fractures verses non-fractures was the same. The presence of fractures of the face does not favor a better outcome.

A study from 2002 (Mosenthal, A.C. 2002) confirmed what was previously believed in regard to the outcome of the elderly with traumatic brain injury. The mortality rate from TBI is higher in the geriatric population at all levels of head injury. There outcome at the time of hospital discharge is worse. This outcome is independent of any other co-factor such as age or other disease.