A blow to the head is referred to by many terms, but the most widely accepted, both within and outside the medical field, is “traumatic brain injury” or TBI. A TBI is most often characterized as “blunt” or “closed” (the latter meaning the skull or cranium was not penetrated). Car accidents are the most common cause of closed TBI’s, but many types of mishaps can result in significant impact to the brain. “Penetrating head trauma” is less common in the civilian world, and would be more so if there were fewer guns, but that’s a topic for another issue. Other injuries can penetrate the skull and injure the underlying brain. For example, being struck by an object while working on a construction site.
As you might imagine, the severity of injury varies, leading to a rough categorization of TBI’s (including concussions) into mild, moderate and severe. TBI’s are defined clinically by doctors using an old, but relatively reliable, scale called the Glasgow Coma Score. However, brain injuries vary, making such a simplistic 12-point rating system somewhat coarse. Ultimately, the nature of an injury boils down to how the forces of the impact are distributed in and affect the brain. This depends on the size and velocity of the impact. A striking example is the great variation in injuries incurred in high-speed motor vehicle accidents (often referred to as MVA’s). Sometimes the face and skull are severely damaged, yet the brain remains relatively protected. Other times, many severe TBI’s occur without a scratch to the face or scalp, yet the forces, for whatever reason, mostly affect the brain tissue, which is fragile. Further complicating matters is the fact that the brain is kind of “floating” in a thin layer of fluid inside the skull, allowing it to “bang” against the inside of the skull repeatedly when the head is forcefully shaken.
The fragile nature of brain tissue goes far beyond its Jell-O-like texture and structure. Of greatest issue is that destroyed neurons lack the capacity to regenerate. In other words, once a neuron dies, it’s gone forever, and new neurons, for the most part, do not occur in the human brain, particularly after early childhood. Although the brain is made up of many types of cells, the ones most important to us are the neurons. Oddly enough, much of the cell (neuron) death does not occur as a result of the initial impact. Instead, the true problem arises often days later when the injured tissue begins to swell. Those of us who have sustained injuries to an extremity might wonder why swelling (called “edema”) is such a serious problem. If we injure an ankle or a wrist, for example, we’re told to elevate it, apply ice, and within a few days healing is underway and the swelling abates. Not so with the brain. Because the brain is in a tightly confined space—the skull—there is no room for it to swell. You don’t have to be a physics whiz to realize that the pressure must rise (think of a beer bottle left in the freezer, except the skull won’t crack like the glass does). It is the elevated “intracranial pressure” (ICP), which can be measured by a monitoring device in many Intensive Care Units, that ultimately causes most of the brain damage. Most frustrating for those who treat brain injuries is that little effective treatment exists for this problem.
Thus, a grim picture emerges: fragile vital tissue is destroyed, little can be done about it, and the tissue has limited capacity for recovery. Therefore, all severe TBI’s, most moderate TBI’s, and a surprising number of mild TBI’s result in deficits in an individual. Given the myriad functions of the brain, these deficits can range from just occasional headaches to what is clinically referred to as a “chronic vegetative state” (where an individual is rendered little more than a body lying in a bed requiring 24-hour care), and virtually everything in between. Disturbances to the sensory systems (sight, smell, hearing, taste, sensation) are common, and these manifest in a number of different ways. Most significant head injuries result in some level of cognitive dysfunction, which is the most debilitating aspect of TBI. While some improvement typically occurs in the first six months to a year after a TBI, full recovery from any but the most minor injuries, is difficult. Yet, some deficits are so subtle that only the individual or persons close to the individual notice.
Concussion
Questions from the doctor are used to determine the severity of the injury and the level of necessity for concern. Questions might include, “do you know what year it is?”, “do you know who the President is?”, or “can you count backwards by tens from 100?” Failure to answer some of these questions after a significant bump on the noggin is not the end of the world, and is usually temporary, as the brain’s cells are theoretically “stunned.”
The strictest definition of a concussion includes a period, however brief, of lost consciousness. This period, which some may call “blacking out” or being “knocked out,” typically involves an inability to process or respond in a meaningful way to stimuli such as sound or touch. Such a loss of consciousness is almost always associated with loss of memory for the events that occurred just before, during, and for some period after the impact. Many of these memories will return, though most people never remember what happened immediately prior to, or after their blow to the head.
The period of memory lost as a result of a concussion is roughly proportional to the amount of time one is “knocked out,” which is roughly proportional to how hard one strikes his head, which is roughly proportional to how much damage was done to some of the brain cells. The great majority of concussions do not cause detectable permanent damage to the brain, although seemingly minor cranial injuries sometimes result in long-term symptoms.
It is also possible to experience a significant blow to the head which does not result in a period of lost consciousness. Some may say they were “stunned” or believe they were “just out of it for a few seconds.” This sort of event may still be referred to as a “concussion.” Blows to the head that render one completely or partially unconscious until an ambulance arrives are much more serious injuries and are a topic for another time.
It is exceedingly rare for one to go his entire life without experiencing at least a “minor concussion” or without being “stunned” by being struck on the head. Particularly active people or those thinking back to their childhood may recall slipping and falling briskly striking the back of the head. This may bring back memories of “seeing stars.”
This experience of “seeing stars” happens because our brains basically “float” in fluid called “spinal fluid,” which is found predominantly in our spinal column, but which is produced in the brain. When our head strikes or is struck by an object, our brain actually bangs up against the inside of our skull. Think of shaking a jar full of water with a golf ball in it—except imagine that the golf ball is soft. The impact of the brain striking the skull can result in the temporary dysfunction or even permanent damage of some of the cells on the surface of the brain where the impact with the skull has occurred. ?Though the brain itself immediately returns to its normal shape, cells throughout the brain might be temporarily or permanently affected, causing a loss of consciousness. The cells responsible for our consciousness lie deep in the brain, far from where the organ might strike the inside of the skull. We may “see stars,” particularly with a hard blow to the back of the head, because the back part of the brain is where our vision is processed. A blow to the back of the head causes the brain to suddenly float backwards, striking the “vision area” against the inside of the back of the skull. While we can tolerate the loss of a small number of cells in certain areas of the brain without any noticeable effects, loss of a few cells in just the right area of the brain can have considerable permanent effects.
Most of us don’t seek or require medical attention for a concussion. If even a small percentage of all concussions were serious, they would represent a major health problem in society, which is not the case. Then again, a relatively minor blow to the head can sometimes fracture the skull, which may result in a torn artery inside of the head. This can cause rapid development of a large blood clot that presses on the brain, often causing coma and even death unless it is removed quickly by a brain surgeon. A period of time during which the person seems perfectly fine may occur between this sort of blow to the head and the development of coma. The blood clot resulting from this scenario is called an “epidural hematoma,” and the time between the blow and the coma is called a “lucid interval.” This is what happened in the sad case of Natasha Richardson, who was reportedly chatting it up with ambulance personnel just before she died.
In the end, the best way to address a head injury is to avoid one in the first place. Take precautions: wear a helmet, even when engaged in an activity that seems unlikely to result in a head injury, such as riding a skateboard or rollerblading. This is especially important for children, especially those under the age of 10 or so, whose brains are not yet fully developed. You would be amazed at the unlikely nature of many severe head injuries that result in the devastation of not only the life of the injured, but those close to the injured as well. Then there are the obvious things, like safe driving practices. Every year, TBI effects many lives in this country at a great cost, and on many levels, financially and otherwise. It is unlikely that significant advances in treatment and recovery will be made in the near future, so BE SAFE!
by Thomas Chappell, MD
