Serious Brain Injuries- The Many Ways the Brain Can Be Injured.
Summary of different brain injuries.
Direct TraumaIn 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 motor vehicle accidents, falls, and sports injuries. While the brain is one of the most complex objects on earth, it is very soft and fragile with a consistency of firm pudding.
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.
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.
INDIRECT TRAUMAMedical 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 INJURYWe 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.
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.
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 OXYGENOur 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 INJURYIn 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.