Here, it is useful to fully quote the standard definition of a traumatic brain injury used by the National Institute of Neurological Disorders and Stroke.
According to NINDS, a TBI
Occurs when a sudden trauma causes damage to the brain. TBI can result when the head suddenly and violently hits an object, or when an object pierces the skull and enters brain tissue. Symptoms of a TBI can be mild, moderate, or severe, depending on the extent of the damage to the brain. A person with a mild TBI may remain conscious or may experience a loss of consciousness for a few seconds or minutes. Other symptoms of mild TBI include headache, confusion, lightheadedness, dizziness, blurred vision or tired eyes, ringing in the ears, bad taste in the mouth, fatigue or lethargy, a change in sleep patterns, behavioral or mood changes, and trouble with memory, concentration, attention, or thinking. A person with a moderate or severe TBI may show these same symptoms, but may also have a headache that gets worse or does not go away, repeated vomiting or nausea, convulsions or seizures, an inability to awaken from sleep, dilation of one or both pupils of the eyes, slurred speech, weakness or numbness in the extremities, loss of coordination, and increased confusion, restlessness, or agitation.
This video helpfully illustrates the concepts spelled out by the federal brain injury experts.
The damage done to the nerves may not show up on MRIs or CAT and PET scans. Anyone in Virginia who files an insurance claim or a personal injury lawsuit over a TBI should at least consult with a brain injury lawyer to learn what types of medical evidence and testimony is needed to establish the existence of a TBI.