Traumatic brain injury

A traumatic brain injury, or TBI, is damage to the brain from an outside force — a blow to the head, a violent jolt, or a penetrating injury. It is one of the most serious injuries in accident cases, and also one of the most disputed, because a mild TBI can leave a person with real, life-changing problems and a normal-looking brain scan.

It is general information, not legal advice, and it is not medical advice.

Mild, moderate, and severe

Doctors classify TBI by how the person presented right after the injury — the depth and length of any loss of consciousness, how disoriented they were, and how much memory they lost around the event.

• Mild TBI (including most concussions): brief or no loss of consciousness, short-lived confusion. Imaging is usually normal. Symptoms often resolve, but not always.
• Moderate TBI: longer loss of consciousness or confusion, often with findings on imaging. Usually a hospital stay and rehabilitation.
• Severe TBI: extended unconsciousness or coma, clear structural damage, intensive care, and long rehabilitation with lasting deficits.

"Mild" describes the initial presentation, not the outcome. A mild TBI can still cause persistent problems.

What it does

Common effects include trouble with memory and concentration, slowed thinking, headaches, dizziness, light and noise sensitivity, sleep problems, fatigue that does not lift with rest, irritability, anxiety, and depression. For many people the cognitive and mood changes — not the headaches — are what disrupt work and relationships.

How it is diagnosed and documented

• The acute record. Paramedic and emergency-department notes describing confusion, repeated questions, amnesia, or loss of consciousness are the anchor.
• Imaging. CT and MRI rule out bleeding and structural damage. Normal results do not rule out a mild TBI. Specialized imaging is sometimes used but is not universally accepted.
• Specialist care. A neurologist, physiatrist, or concussion clinic directing treatment.
• Neuropsychological testing. A battery of standardized tests that measures memory, attention, processing speed, and executive function against expected performance.
• Before-and-after accounts. Short statements from family, friends, and coworkers describing concrete changes — missed appointments, lost job performance, personality shifts.

Causation and pre-existing conditions

The defense will look for another explanation: an earlier head injury, a learning disability, depression, ADHD, substance use, or normal aging. A prior condition does not defeat the claim. If the accident made an existing condition worse, the responsible party owes that worsening, and an unusually vulnerable person is still owed for the full injury caused.

Sources: CACI No. 3927 (aggravation of a pre-existing condition); CACI No. 3928 (unusually susceptible plaintiff). CACI citations are to the Judicial Council of California Civil Jury Instructions (2026 edition).

Which accidents cause TBI

A TBI can come from any hard impact or violent motion of the head. It comes up across car accidents, truck accidents, motorcycle accidents, pedestrian accidents, bicycle accidents, rideshare accidents, and falls and other premises injuries.

Common questions

Can I have a brain injury if my CT scan was normal?

Yes. A standard CT or MRI often looks normal after a mild traumatic brain injury even when a person has real, lasting problems with memory, attention, mood, and fatigue. Diagnosis in that situation relies on the clinical history and neuropsychological testing.

Why does the insurer dispute a mild TBI?

Because the evidence is often not a picture. The defense points to normal imaging, argues the symptoms come from stress or a pre-existing condition, or says a brief or absent loss of consciousness rules it out. None of those arguments is medically correct, but they are common.

What documents a brain injury?

The earliest records — paramedic and ER notes describing confusion, amnesia, or loss of consciousness — plus treatment with a neurologist or physiatrist, formal neuropsychological testing, and statements from people who knew the person before and after.

How long do TBI symptoms last?

It varies widely. Many people recover in weeks to months. Some have symptoms that persist for a year or longer or that do not fully resolve. That is a medical question for the treating specialists, not something a web page or a lawyer can predict.