A concussion is a brain injury caused either by a direct blow to the head or by violent shaking of the head. During a car accident, especially when the driver is restrained, the head may shake from the impact. This may result in a back-and-forth movement of the brain within the skull, often referred to as coup-contrecoup injury. The brain is protected by a layer of liquid called the cerebrospinal fluid, which surrounds the brain and spinal cord and acts as a cushion and shock absorbent. In a case of severe head trauma, often resulting from a direct blow to the head, the brain can shake so violently that the surface of the brain may actually collide with the inside of the skull resulting in bruising, referred to as contusion. This is often seen on a brain MRI. However, during mild head trauma, or concussion without direct head trauma, the cerebrospinal fluid absorbs the shock and the brain shakes within the fluid. Depending on the severity of the concussion, this may or may not result in disruption of the fibers that connect different brain regions. In addition, the vestibular system, which is part of the inner ear, contains delicate structures that could be disrupted by head trauma. As a result, patients with concussion often report headache, ringing in the ears, nausea, vomiting, balance problems, fatigue, drowsiness, blurry vision, photophobia (sensitivity to light), cognitive difficulties such as trouble with concentration and memory, irritability, and mood changes. Some of these symptoms may be caused by vestibular dysfunction and others by the impact on the brain.
Symptoms related to concussion often improve within a week or two but may persist longer in case of more severe head trauma. Recovery of the disrupted brain fibers and restoration of the internal structures in the vestibular system account for the improvement in symptoms. Several forms of therapy that target specific symptoms have been found to be very helpful in expediting the recovery, including vestibular therapy, physical therapy, and vision therapy, and in some cases, cognitive therapy. Recovery from concussion is a continuous and gradual process. Specific symptoms tend to improve slowly until full recovery and once a symptom subsides, it typically does not recur. Improvement in symptoms is typically associated with increased level of activity of the patient until the level of functioning is back to baseline.