Concussion is derived from the Latin word concussus
, which means to shake violently. Initially, it was thought to produce only a temporary disturbance of brain function due to neuronal, chemical, or neuroelectrical changes without gross structural change. We now know that structural damage with loss of brain cells does occur with some concussions. In the last several years, the neurobiology of cerebral concussion has been advanced predominantly in animal studies but also in studies in man as well. It has become clear that, in the minutes to days after concussive brain injury, brain cells that are not irreversibly destroyed remain alive but in a vulnerable state. These cells are particularly vulnerable to minor changes in cerebral blood flow, increases in intracranial pressure, and especially anoxia. Animal studies have shown that, during this period of vulnerability, which may last as long as a week with a minor head injury such as a concussion, a minor reduction in cerebral blood flow that would normally be well tolerated now produces extensive neuronal cell loss.1–5
This vulnerability appears to be due to an uncoupling of the demand for glucose, which is increased after injury, with a relative reduction in cerebral blood flow. While the precise mechanisms of this dysfunction are still not fully understood, it is now clear that, although concussion in and of itself may not produce extensive neuronal damage, the surviving cells are in a state of vulnerability characterized by a metabolic dysfunction, which can be thought of as a breakdown between energy demand and production. Precisely how long this period of metabolic dysfunction lasts is not presently fully understood. Unfortunately, there are today no neuroanatomic or physiologic measurements that can be used to precisely determine the extent of injury in concussion or the severity of metabolic dysfunction or precisely when it has cleared. It is this fact that makes return-to-play decisions after a concussion a clinical judgment.
Team physicians, athletic trainers, and other medical personnel responsible for the medical care of athletes face no more challenging problem than the recognition and management of concussion. Indeed, such injuries have captured many headlines in recent years and have spurred studies within both the National Football League and the National Hockey League.
When discussing concussion, we must realize that there is no universal agreement on the definition and grading of concussion.1,6–8
Tables – present different attempts at grading concussion, all focusing on loss or nonloss of consciousness and posttraumatic amnesia (PTA) as hallmarks in the grading schemes. Furthermore, they may not give enough attention to the other signs and symptoms of concussion. As we all know, a patient with concussion may display any combination of the following signs and symptoms: a feeling of being stunned or seeing bright lights, brief loss of consciousness, lightheadedness, vertigo, loss of balance, headaches, cognitive and memory dysfunction, tinnitus, blurred vision, difficulty concentrating, lethargy, fatigue, personality changes, inability to perform daily activities, sleep disturbances, and motor or sensory symptoms.
Table 1 Cantu Grading System for Concussion9*
Table 2 Colorado Medical Society Grading System for Concussion10
Table 3 AAN Practice Parameter (Kelly and Rosenberg) Grading System for Concussion6
Table 4 Jordan Grading System for Concussion11
Table 5 Ommaya Grading System for Concussion12
Table 6 Nelson Grading System for Concussion7
Table 7 Roberts Grading System for Concussion8
Presently, there is no universal agreement that PTA is a better or more sensitive predictor of outcome after traumatic brain injury than depth and duration of unconsciousness,14–16
but many consider the duration of PTA the best indicator of traumatic brain injury severity15,17
and the most dependable marker of outcome prediction,18–25
even in mild cases.16,26
While variously described by different investigators, PTA includes impaired orientation, that is, retrograde amnesia and anterograde amnesia.22,27–29
Recently, some investigators16,30–32
have suggested that PTA might better be called posttraumatic confusional state.
Posttraumatic amnesia may be divided into 2 types. The first type of PTA is retrograde, defined by Cartlidge and Shaw23
as a “partial or total loss of the ability to recall events that have occurred during the period immediately preceding brain injury.” The duration of retrograde amnesia usually progressively decreases. The second type of PTA is anterograde amnesia, a deficit in forming new memory after the accident, which may lead to decreased attention and inaccurate perception. Anterograde memory is frequently the last function to return after the recovery from loss of consciousness.33
Memory and new learning are believed to involve the cerebral cortex, subcortical projections, hippocampal formation (gyrus dentatus, hippocampus, and parahippocampal gyri), and the diencephalons, especially the medial portions of the dorsomedial and adjacent midline nuclei of the thalamus.34
In addition, frontal lobe lesions may cause alterations in behavior, including irritability, aggressiveness, and loss of inhibition and judgment. Recently, evidence has been presented that the right frontal lobe plays a prominent role in sustained attention.35
The lack of a universal definition or grading scheme for concussion renders the evaluation of epidemiologic data extremely difficult. As a neurosurgeon and team physician, I have evaluated many football players who suffered a concussion. Most of these injuries were mild, not involving loss of consciousness, and were associated with PTA, which was helpful in making the diagnosis, especially in mild cases.
I developed a practical scheme for grading concussion severity based on the duration of unconsciousness or PTA (or both), which has worked well on the field and sideline (see Table ). The most mild concussion (grade 1) occurs without loss of consciousness, and the only neurologic deficit is a brief period of posttraumatic confusion or PTA, which, by definition, lasts less than 30 minutes. The moderate (grade 2) concussion is usually associated with a brief period of unconsciousness, by definition, not exceeding 5 minutes. Less commonly, consciousness is not lost; the athlete instead experiences a protracted period of PTA lasting more than 30 minutes but less than 24 hours. A severe (grade 3) concussion occurs with a more protracted period of unconsciousness lasting longer than 5 minutes. Rarely, it may occur without a loss of consciousness or with a shorter period of unconsciousness but with a very protracted period of PTA lasting more than 24 hours. In reality, prospective studies over the last several years have shown that virtually all concussions are grade 3 by this guideline because of PTA lasting longer than 24 hours (D. Erlanger, unpublished data, 2000). A protracted period of unconsciousness lasting more than 5 minutes is almost never seen on athletic fields; most periods of unconsciousness last seconds to a minute. Prospective studies over the last 10 years have demonstrated a correlation between the duration of postconcussive symptoms and PTA and abnormal results on neuropsychological tests. Therefore, I present an evidence-based modification of the original Cantu guidelines9
Evidence-Based Cantu Grading System for Concussion
When checking for orientation and retrograde amnesia on the field, asking the athlete the current quarter, the score, what happened, and the names of the current and last week's opponents is useful. When checking for attention or anterograde amnesia deficits, useful tests are repeating 4 words immediately and 2 minutes later, repeating 5 numbers forward and especially backward, and repeating months of the year backward.
Recently, computer-administered minineuropsychological tests have been proposed as a more feasible way to conduct group baseline assessments,36,37
as well as a personal digital assistant version that can be connected to the Internet.38,39
Thus, while not yet the standard of care, neuropsychological tests (with a preseason baseline and serial postconcussion assessments) are assisting clinicians in concussion management, including return-to-play decisions.
Whether an athlete has been unconscious is, of course, important. It is generally believed that the degree of brain injury sustained is indicated by the depth and duration of coma.40–42
However, the coma referred to by these authors is not the seconds to minutes usually seen on the athletic field but rather hours' or days' duration. Thus, while not diminishing the importance of being rendered unconscious, I find it illogical to grade a concussion that produces postconcussion symptoms lasting months or years without loss of consciousness as less severe than a concussion resulting in brief unconsciousness and resolution of all postconcussion symptoms within a few minutes or hours. Brett Lindros, Al Toon, Jim Miller, Steve Young, and Merrill Hodge are professional athletes whose careers were ended by concussions without loss of consciousness that produced sustained postconcussion symptoms. We know these athletes consider their concussions very severe.