Concussion is diagnosed clinically, from a careful history and a targeted examination of vestibular (balance), oculomotor (eye movement), cognitive and movement function. That is because no single scan shows it. CT and MRI rule out bleeding and structural lesions. So a normal scan starts the evaluation rather than ending it.
There is no single scan that says “concussion.” That is usually delivered to patients as though it meant the injury cannot be established. It means the opposite. The diagnosis rests on a careful history and a targeted examination. So who performs the assessment matters a great deal.
Does a concussion show up on a CT scan?
A head CT in the emergency department is looking for bleeding, skull fracture and mass effect. Those findings change what happens that night. The CENTER-TBI series covered over 4,000 admission scans. The most frequent findings were traumatic subarachnoid hemorrhage (45.3%), skull fracture (37.4%), contusion (31.3%) and acute subdural hematoma (28.9%). All were up to three times more common in moderate-severe injury than in mild.
CT is insensitive to concussion itself, and this is by design. Concussion is a diffuse functional and microstructural disturbance. There is no lesion for the scanner to pick up. A normal CT means you are not in surgical danger. It is the beginning of the evaluation, not the end of it.
Vande Vyvere T, et al. Imaging Findings in Acute Traumatic Brain Injury (CENTER-TBI). J Neurotrauma. 2024;41(19-20):2248–2297. doi:10.1089/neu.2023.0553
When is an MRI useful after a concussion?
MRI picks up lesions CT misses. So it moves some patients from uncomplicated to complicated mild TBI. That has genuine prognostic value (it helps predict the outcome). But that value is smaller, and more specific, than patients expect.
A prospective cohort followed 113 adults for a year. They were imaged 3–17 days after mild TBI. Those with intracranial lesions returned to work at a median of 17 days versus 6. They also reported more symptoms (RPQ 12.0 vs 6.5). The delay was greatest, about 31 days, where multiple lesion types appeared on MRI or where the initial CT was positive. But the authors were explicit that a single intracranial lesion did not predict work disability. Overall return to work at one year was 98%.
So MRI is worth doing when the clinical picture is not explaining itself. It is also worth doing when symptoms are not following the expected course, or when the burden of injury needs documenting. It is not worth doing to confirm a concussion. That is because a normal MRI is the expected result in an uncomplicated concussion and proves nothing about symptoms.
Huovinen A, et al. Return to work after mild traumatic brain injury: association with positive CT and MRI findings. Acta Neurochir. 2022;164(7):1707–1717. doi:10.1007/s00701-022-05244-4
Is there a blood test for concussion?
GFAP and UCH-L1 are validated to exclude a structural lesion visible on CT, within 12 hours of injury. Their negative predictive value is around 97%. They are excellent at that job. They are not a blood test for concussion. Every validation study used an abnormal CT as the reference standard. Timing and age both change what a result means.
Full detail on what the biomarkers show and when →
How are balance and eye movements tested after a concussion?
The most productive examination in persistent concussion is of the vestibulo-ocular system. That is how the eyes and the balance system work together. Dysfunction here is common and strongly associated with longer recovery. It is also invisible to imaging.
Videonystagmography (VNG) uses infrared goggles to record eye movements you cannot control. It tests inner-ear and central motor function:
- Ocular testing — tracking eye movement as the patient follows visual targets
- Positional testing — watching eye movement as head and body position change
- Caloric testing — stimulating each ear separately, so a difference between sides can be measured rather than just reported
One study looked at children and adolescents at a multidisciplinary concussion program. Vestibulo-ocular dysfunction was present in 28.6% of acute cases. It was present in 62.5% of those already in post-concussion syndrome. It carried roughly four times the odds of developing post-concussion syndrome. Those with it had a median symptom duration of 40 days rather than 21.
Ellis MJ, et al. J Neurosurg Pediatr. 2015;16(3):248–255. doi:10.3171/2015.1.PEDS14524
Why am I still dizzy days or weeks after a concussion?
Dizziness in the first few days is common and usually fades as the brain’s energy crisis settles. When it is still there after a week or two, or it comes on when you turn your head, roll over in bed or walk down a busy store aisle, it usually has a source that can be found: the inner ear, the eye-movement system, the upper neck, or the way the brain merges those three signals.
Each source shows up differently. Inner-ear crystals knocked loose by the blow produce brief spinning with position changes, which the positional part of VNG catches, and they are treated with repositioning maneuvers rather than rest. A gaze or balance-integration deficit shows up on VNG and measured posture, and it responds to the targeted rehabilitation described in concussion treatment. Dizziness that travels with neck pain and a skull-base headache points at the neck, the problem sorted out in occipital neuralgia vs concussion.
Other tools in current use
- Quantitative EEG (qEEG) and functional MRI — assess brain function rather than structure. They are used to describe a picture, not to confirm a diagnosis. They are the closest ordinary practice comes to observing the neurometabolic disturbance directly.
- Computerized neuropsychological testing — reaction time, memory and processing speed. It is most useful where there is a baseline to compare against.
- Impact sensors — instrumented mouthguards and similar wearables that record the force and direction of a hit in real time. They are useful in organized sport and irrelevant to the adult injured in a collision. They are not a diagnostic test in either case.
- Biomarker assays — an active research area beyond the validated GFAP/UCH-L1 rule-out, including work with saliva. Promising, but not yet standard of care.
We name the last two honestly. Impact sensors and emerging biomarkers are genuinely useful lines of work. But neither replaces a clinical examination today. Any clinic implying otherwise is overselling.
How are memory and thinking tested after a concussion?
The Montreal Cognitive Assessment (MoCA) is a structured screen of attention, memory, executive function, language and orientation. Its weakness is that it is only as good as the person giving it. Scoring drifts without training. Dr. Gurpreet Singh Padda, MD, MBA, MHP, is a certified MoCA rater. That means the test is scored to standard. Where a return-to-work decision or a claim turns on cognitive findings, that difference is material.
Cognivue is a computerized cognitive assessment. The patient works through an adaptive visual test rather than being interviewed. That removes examiner variability entirely. It produces a quantified profile across domains, including memory, visuospatial processing and reaction time. Because the patient takes it alone and it can be repeated, it is well suited to tracking change across visits rather than giving a single verdict.
Used together, they answer different questions. MoCA gives a clinician-scored screen against a familiar benchmark. Cognivue gives a quantitative profile that does not depend on the examiner. It can be repeated without practice effects taking over.
Movement and balance: Kinetisense
Balance deficits after concussion are real, and eyeballing them is unreliable. Kinetisense is a motion-capture system that needs no markers: no sensors are attached to the patient. It measures posture, balance and functional movement from video. It produces numbers where clinical assessment usually produces impressions.
That matters here for two reasons. Clinically, objective balance data tracks recovery. It shows when a patient is not ready to return to load. Evidentially, a measured postural deficit is a finding that exists independently of what the patient reports. That is precisely what is missing from most concussion records.
Structured symptom instruments
Concussion symptoms are largely reported rather than observed. That makes them easy to dismiss and easy to dispute. We use the same instruments at intake and follow-up, so the trajectory is documented rather than described. We use RPQ and BC-PSI for post-concussive symptoms, and PCL-5 or CAPS-5 where trauma symptoms are also present. See PTSD and post-concussion syndrome.
What the assessment is for
Two things at once. Clinically, it identifies which systems are affected, so treatment can be aimed rather than general. Evidentially, it turns “I still don’t feel right” into a record: objective findings, quantified deficits, and direction of change over time.
Common questions
Can a brain MRI detect a concussion?
Usually not. A normal MRI is the expected result in an uncomplicated concussion. MRI’s value is finding lesions CT missed in complicated mild TBI. There, multiple lesion types predict a longer return to work. It is not a confirmatory test for concussion.
Why was my CT normal if I have a concussion?
Because CT is a test for bleeding, fracture and mass effect, not for concussion. Concussion is a functional injury with no lesion for the scanner to pick up. A normal CT tells you that you are not in surgical danger.
What the emergency CT is looking for is covered in TBI Doctor in St. Louis: Traumatic Brain Injury Evaluation.
What is the difference between MoCA and Cognivue?
A clinician gives and scores MoCA against a familiar benchmark. How reliable it is depends on rater training. That is why certification matters. Cognivue is computerized, and the patient takes it alone. That removes examiner variability. It produces a quantified profile that can be repeated. The two complement each other rather than substituting for each other.
Do I need all of these tests?
No. The history directs the assessment. Someone whose symptoms are dominated by dizziness and visual intolerance needs the vestibular and oculomotor work. Someone whose main problem is concentration and memory needs the cognitive side. We do not run a fixed panel.
How each finding shapes the treatment plan is covered in Concussion Treatment.
What will the ER do for a concussion?
The emergency department checks for injuries that need action that night. A head CT looks for bleeding, a skull fracture or a mass effect. Within 12 hours of injury, a GFAP and UCH-L1 blood test can help rule out a lesion that would show on CT. Neither test confirms or excludes a concussion itself. So a clean result means you are not in surgical danger, not that you are uninjured.
How do doctors check your eyes for a concussion?
Eye movements are tested with videonystagmography. It uses infrared goggles to record involuntary eye movement. You follow visual targets and change head and body position. Each ear is stimulated separately, so a difference between sides can be measured. Problems in how the eyes and balance system work together are common after concussion. They are linked to a longer recovery and do not show on imaging.
Is there a two-minute concussion test?
Quick screens exist, and they are built for the sideline: a symptom checklist, a few recall items, a timed eye-movement or balance check. Their job is to flag who needs a proper examination. Passing one does not rule a concussion out, least of all in an adult seen days after a crash with no baseline score to compare against. The examination that settles the question takes longer because it tests each system separately.
The roadside habit of sorting injuries by whether someone blacked out fails the same way: concussion without loss of consciousness.
Can I test myself for a concussion at home?
You cannot diagnose it at home, but you can collect what the examiner needs. Write down what happened and how you felt in the first hour. Then score your headache, fog, dizziness, sleep and tolerance for light and noise once a day; a written trend is worth more at a first visit than memory. Eye movements, inner-ear function and balance cannot be measured at home, and that is where most persistent problems turn up. A worsening headache, repeated vomiting or growing drowsiness is not something to monitor at home at all.
Learn more: the daily symptom log from our ketogenic diet article.