Concussion (Mild TBI): Symptoms, Diagnosis, MRI Findings and Recovery

What Is a Concussion?

A concussion is a form of mild traumatic brain injury (mTBI) caused by a direct blow to the head or by sudden acceleration, deceleration, or rotational forces affecting the brain.

Concussion can occur during falls, road traffic accidents, sports injuries, assaults, or other traumatic events. A direct impact to the skull is not required. Sudden movement of the head can produce sufficient forces to disturb normal brain function.

How Does a Concussion Affect the Brain?

Concussion causes a rapid disturbance of neuronal activity following mechanical forces applied to the brain.

Acceleration, deceleration, and rotational forces may stretch neuronal membranes and axons, producing changes in normal cellular function.

The acute neurometabolic response includes:

• Abnormal ion movement across neuronal membranes.
• Increased release of excitatory neurotransmitters, particularly glutamate.
• Changes in cellular energy requirements and mitochondrial function.
• Temporary disturbances of neuronal signaling and communication between brain networks.
• Altered regulation of cerebral blood flow and energy metabolism in some patients.

These disturbances can produce headache, confusion, dizziness, cognitive slowing, and other neurological symptoms.

The degree of cellular dysfunction varies between patients. In uncomplicated concussion, recovery usually occurs without visible structural abnormalities on conventional imaging.

Concussion is a genuine traumatic brain injury even when CT and MRI are normal.

Does a Concussion Cause Structural Brain Damage?

Concussion and mild traumatic brain injury are closely related terms, but mild TBI can occur with or without visible structural intracranial injury. Because of that two clinical situations should be distinguished.

Uncomplicated Concussion

In uncomplicated concussion, the clinical findings support an acute traumatic disturbance of brain function, but conventional imaging does not demonstrate an associated structural intracranial lesion.

The patient may experience headache, dizziness, confusion, amnesia, or cognitive difficulties despite normal CT or MRI findings.

This is the typical presentation of concussion.

Mild TBI With Structural Intracranial Injury

Some patients have an initial clinical presentation consistent with mild TBI, but imaging demonstrates additional traumatic lesions, such as:

• Brain contusions.
• Traumatic subarachnoid hemorrhage.
• Small subdural or epidural hematomas.
• Intraparenchymal hemorrhage.
• Traumatic microbleeds or axonal injury.

This presentation is often described as complicated mild traumatic brain injury. A patient may initially have a Glasgow Coma Scale (GCS) score of 13–15 despite an associated intracranial lesion.

The distinction matters because the nature of the structural injury may influence treatment, observation, and prognosis. A high initial GCS score does not exclude a clinically important traumatic intracranial lesion.

A structural injury must be assessed according to its location, extent, associated abnormalities, and neurological consequences.

A concussion may occur with an associated skull fracture, even when CT or MRI shows no structural injury to the brain itself. A skull fracture does not exclude concussion, but the diagnosis of concussion still requires evidence of an acute disturbance of brain function. An isolated skull fracture should be assessed separately from intracranial traumatic lesions.

For a detailed discussion of persistent headaches, vertigo, cognitive difficulties, and treatment, see Post-Concussion Syndrome: Persistent Symptoms, Causes and Treatment. For injury classification, structural brain injury, causation, and long-term functional assessment, see Medicolegal Significance of Concussion and Mild Traumatic Brain Injury.

Is Loss of Consciousness or Amnesia Required?

No. Concussion can occur without loss of consciousness or amnesia. Some patients remain awake and able to communicate immediately after the injury but experience confusion, disorientation, impaired concentration, or a feeling of being dazed. Others develop headache, dizziness, fatigue, or sleep disturbances during the hours following trauma.

However, symptoms such as headache or dizziness alone are nonspecific. The diagnosis requires an appropriate injury mechanism and clinical evidence consistent with an acute traumatic disturbance of brain function.

Common Symptoms of Concussion

The symptoms of concussion vary according to the patient and the injury.

Physical Symptoms

• Loss of consciousness (LOC) — may occur immediately after injury but is not required for the diagnosis of concussion.
• Headache or pressure in the head.
• Dizziness or imbalance.
• Nausea and occasionally vomiting.
• Sensitivity to light or sound.
• Blurred vision or visual discomfort.
• Fatigue and reduced exercise tolerance.

Cognitive Symptoms

• Confusion or disorientation.
• Difficulty concentrating.
• Slower information processing.
• Short-term memory difficulties.
• Mental fatigue during reading or other cognitive tasks.

Sleep and Emotional Symptoms

• Difficulty falling asleep or disrupted sleep.
• Increased sleep duration or persistent tiredness.
• Irritability or emotional sensitivity.
• Anxiety or mood changes.

Symptoms may appear immediately or become more noticeable during the following hours or days.

The type and severity of symptoms do not reliably establish whether structural brain injury is present. Imaging and neurological examination are used when additional traumatic lesions are suspected.

How Is a Concussion Diagnosed?

Concussion is primarily a clinical diagnosis.

The assessment combines the circumstances of the injury, acute neurological findings, symptom history, and physical examination.

Three elements are particularly important.

Mechanism of Injury

The traumatic event must be compatible with forces capable of disturbing brain function.

Examples include:

• Direct head impact.
• Falls.
• Road traffic accidents.
• Sports collisions.
• Rapid acceleration, deceleration, or rotation of the head.
• Blast-related trauma.

A direct blow to the head is not essential.

Acute Neurological Disturbance

Findings may include confusion, disorientation, altered mental state, post-traumatic amnesia, or loss of consciousness. Other acute neurological signs, including disturbances of balance or coordination, may support the diagnosis. Documenting the patient’s neurological condition shortly after injury is particularly valuable.

Clinical Examination

The physician assesses consciousness, orientation, memory, neurological function, balance, eye movements, and other findings relevant to the injury. The examination also helps identify possible cervical injury or additional neurological abnormalities. Headache, dizziness, nausea, and fatigue are important symptoms, but they must be interpreted in the context of the injury.

Concussion is a clinical diagnosis. CT is performed when there is a risk of associated intracranial injury, particularly hemorrhage or brain contusion, rather than to confirm concussion itself. A normal CT or MRI does not exclude concussion.

What Is the Glasgow Coma Scale’s Role in Concussion?

The Glasgow Coma Scale (GCS) assesses eye opening, verbal response, and motor response.

A GCS score of 13–15 is commonly associated with mild traumatic brain injury, but the score must be interpreted together with the clinical history and associated findings. GCS is particularly useful for monitoring neurological status after trauma.

However, it has limitations:

• A patient may have a GCS of 15 despite concussion.
• Amnesia or cognitive difficulties may persist despite normal consciousness.
• Intracranial hemorrhage or contusion may coexist with a relatively preserved initial GCS.
• Neurological deterioration may occur after an initially stable examination.

The clinical significance of the injury depends on more than the GCS score alone.

CT and MRI After Concussion: What Can They Show?

CT and MRI answer different diagnostic questions.

Neither examination directly demonstrates the functional disturbance responsible for most uncomplicated concussions.

CT Scan After Head Injury

CT is the principal initial imaging examination when acute traumatic intracranial injury is suspected.

It can identify:

• Epidural and subdural hematomas.
• Traumatic subarachnoid hemorrhage.
• Hemorrhagic brain contusions.
• Significant brain swelling and mass effect.
• Many skull fractures.
• Other acute structural abnormalities.

CT is rapid and particularly valuable in emergency assessment. However, a normal CT does not exclude concussion or all forms of traumatic brain injury.

MRI After Concussion

MRI provides greater sensitivity than CT for certain traumatic lesions, particularly small contusions, nonhemorrhagic abnormalities, and selected patterns of traumatic axonal injury. Routine MRI sequences include T1, T2, FLAIR, DWI, and other sequences according to the clinical question and local protocol. MRI may be useful when neurological findings remain unexplained, a structural lesion is suspected, or previous imaging requires clarification.

MRI is not routinely required for every patient with uncomplicated concussion.

Specialized MRI Sequences

Selected MRI sequences may provide additional information when traumatic axonal injury or small hemorrhagic lesions are suspected.

• SWI (Susceptibility-Weighted Imaging): particularly sensitive to small hemorrhagic lesions and traumatic microbleeds.
• DWI (Diffusion-Weighted Imaging): may demonstrate certain acute nonhemorrhagic traumatic lesions.
• DTI (Diffusion Tensor Imaging): evaluates white-matter microstructure, but its findings are not sufficiently specific for routine confirmation of traumatic axonal injury in an individual patient.

Specialized imaging must be interpreted alongside the mechanism of injury, neurological examination, and other imaging findings. More advanced imaging does not automatically provide a more definitive diagnosis.

Blood Biomarkers of Traumatic Brain Injury

Blood biomarkers such as GFAP (glial fibrillary acidic protein) and UCH-L1 (ubiquitin C-terminal hydrolase L1) may help identify patients at low risk of acute traumatic intracranial lesions. In selected adults with suspected mild TBI, these tests can assist in deciding whether a head CT is necessary, particularly when performed within the first 12 hours after injury. Blood biomarkers do not independently diagnose concussion or replace neurological examination and CT when clinically indicated.

Diffuse Axonal Injury and Mild Traumatic Brain Injury

Traumatic axonal injury results from mechanical forces that stretch or damage axons, particularly during rapid rotation, acceleration, or deceleration of the head. For example, this may occur in a car accident when the head suddenly changes direction, in a motorcycle crash, or during a sports collision. These forces can damage axons, particularly at the junction between gray and white matter, within the corpus callosum, or, in more severe injuries, the brainstem.

Depending on severity and distribution, traumatic axonal injury may contribute to disturbances of consciousness, attention, processing speed, memory, and other neurological functions.

MRI may identify:

• Small hemorrhagic lesions within white matter.
• Nonhemorrhagic lesions with diffusion abnormalities.
• Characteristic abnormalities involving structures such as the corpus callosum.

However, microscopic axonal injury may remain undetectable using conventional imaging. MRI findings must also be interpreted carefully. Small white-matter abnormalities are not necessarily traumatic, and diffusion-based changes are not always specific to axonal injury.

Traumatic axonal injury is an important consideration in selected patients, but it should not be assumed solely because symptoms persist despite normal imaging. The interpretation of DAI, its distribution, and its clinical consequences requires correlation between imaging and neurological findings.

When Is CT or MRI Necessary After Concussion?

Imaging is considered according to clinical findings, risk factors, and established decision rules.

Important reasons for acute imaging assessment may include:

• Reduced or deteriorating level of consciousness.
• Focal neurological deficits.
• Suspected skull fracture.
• Seizures following trauma.
• Repeated vomiting or other concerning symptoms.
• Significant concern for intracranial bleeding.
• Anticoagulant use or other relevant bleeding risk.

In patients with uncomplicated concussion and no clinical indications for imaging, CT or MRI may not be necessary.

The decision to obtain imaging should be based on the risk of an associated structural injury, not simply on the diagnosis of concussion. When symptoms persist or new abnormalities appear, reassessment may indicate further imaging or specialist evaluation.

Concussion With Associated Skull Fracture

Concussion may occur together with a skull fracture. An isolated fracture does not necessarily indicate structural injury to the brain parenchyma, but its location and associated findings may have important clinical consequences.

Particular attention is required when imaging or examination suggests:

• Depressed skull fracture.
• Pneumocephalus.
• Cerebrospinal fluid leakage from the nose or ear.
• Associated intracranial hemorrhage.
• Possible injury involving the skull base.

Leakage of cerebrospinal fluid (CSF), the fluid surrounding the brain and spinal cord, or traumatic pneumocephalus (air inside the skull) may indicate an abnormal communication between the intracranial space and the outside environment, creating a risk of persistent CSF leakage and central nervous system infection, particularly bacterial meningitis.

These findings may require urgent neurosurgical evaluation even when the patient initially has a relatively preserved level of consciousness.

Concussion Treatment — The First 24–48 Hours

Initial treatment focuses on identifying dangerous associated injuries, monitoring neurological status when necessary, and supporting recovery.

For uncomplicated concussion, relative physical and cognitive rest during the first 24–48 hours is generally appropriate. Relative rest means reducing activities that substantially aggravate symptoms while allowing light daily activities as tolerated. Prolonged strict bed rest or complete isolation is not recommended.

Initial management may include:

• Reduction of physically and cognitively demanding activities.
• Limited screen exposure if it aggravates symptoms.
• Adequate hydration and regular sleep.
• Appropriate treatment of headache and nausea.
• Avoidance of alcohol and activities carrying a risk of another head injury.
• Observation for new or progressive neurological symptoms.

Early management should support neurological recovery without unnecessary prolonged inactivity.

Gradual Return to Physical and Cognitive Activity

After the initial period of relative rest, patients should usually begin a gradual return to ordinary activities. Light physical activity, such as walking, may be introduced according to tolerance. Activity can then be increased progressively, avoiding substantial or prolonged worsening of symptoms.

For students and employed adults, this may require temporary adjustments in:

• Working hours or academic workload.
• Screen use and reading duration.
• Physical exertion.
• Tasks requiring prolonged concentration.
• Activities involving balance or coordination.

Recovery should be guided by symptoms, examination findings, and the demands of the intended activity.

Returning to driving, operating dangerous equipment, or performing work with significant safety risks requires consideration of persistent dizziness, cognitive impairment, visual disturbances, and medication effects.

When Can Patients Return to Sports?

Return to sports requires particular care because of the possibility of another head injury before recovery. A gradual return-to-sport protocol should be followed, with medical clearance before activities involving significant risk of contact, collision, or falls. Returning to contact sports while concussion-related symptoms or neurological abnormalities persist is unsafe.

Second Impact Syndrome and Repeated Head Injury

A second head injury occurring before recovery from concussion may have serious consequences. The term second impact syndrome describes a rare and controversial clinical entity involving rapid cerebral swelling after a subsequent injury, reported predominantly in younger athletes. Although its precise mechanisms and diagnostic boundaries remain debated, the risk of serious consequences from repeated head trauma is well recognized.

Repeated concussions also require assessment of cumulative symptoms, previous recovery patterns, and the risks associated with future exposure. Patients should not return to activities carrying a substantial risk of head impact before appropriate recovery and medical clearance.

How Long Does Recovery From Concussion Take?

Most patients improve substantially within days to weeks following concussion. Recovery time varies with age, the nature of the injury, initial symptom severity, previous concussion history, migraine, sleep disturbances, and associated medical conditions. Some patients recover quickly, while others experience a slower return to normal physical and cognitive function.

Persistent symptoms may include headache, dizziness, fatigue, concentration difficulties, and sleep disturbance. When symptoms do not progressively improve over the first few weeks, further assessment is appropriate. The important question is whether symptoms are following the expected recovery course or whether additional causes require treatment.

When Concussion Symptoms Persist

Some patients continue to experience symptoms beyond the usual recovery period. This condition is commonly described as post-concussion syndrome or persistent post-concussion symptoms.

Persistent complaints may arise from several mechanisms:

• Migraine-like or other post-traumatic headache disorders.
• Cervical muscle, joint, or peripheral nerve injury.
• Vestibular disorders, including post-traumatic BPPV.
• Visual and oculomotor dysfunction.
• Persistent cognitive difficulties.
• Sleep disturbances, fatigue, and emotional symptoms.
• Associated neurological injury in selected patients.

Persistent symptoms require assessment of their specific causes.

For example, positional vertigo caused by BPPV requires different treatment from vestibular migraine. Similarly, cervicogenic headache or occipital neuralgia should be distinguished from migraine-like post-traumatic headache. These conditions may coexist.

The separate article Post-Concussion Syndrome: Persistent Symptoms, Causes and Treatment examines persistent headache, vertigo, cognitive difficulties, normal MRI findings, and targeted treatment in greater detail.

Prognosis After Concussion

The prognosis of uncomplicated concussion is generally favorable. Most patients recover without major lasting neurological limitations. However, the recovery course depends on several factors:

• Severity and characteristics of the initial injury.
• Presence of associated intracranial lesions.
• Previous concussion history.
• Headache and migraine disorders.
• Associated cervical or vestibular injury.
• Sleep and emotional disturbances.
• Persistent symptoms and their effect on daily activities.

When structural abnormalities are present, prognosis must consider the specific lesion rather than relying solely on the initial designation of mild TBI. A small hemorrhagic lesion, an isolated contusion, and widespread axonal injury may have very different clinical consequences. Imaging findings, neurological examination, and the course of recovery must be considered together. Patients who experience prolonged symptoms may continue to improve with appropriate treatment and rehabilitation.

Red Flags — When Urgent Medical Assessment Is Needed

Concussion may initially appear relatively mild, but some patients have associated injuries that become clinically apparent later.

Urgent assessment is required for:

• Progressively worsening or severe headache.
• Repeated vomiting.
• Increasing confusion or drowsiness.
• New weakness, numbness, or speech disturbance.
• Seizures.
• New visual loss or other focal neurological deficits.
• Reduced consciousness or neurological deterioration.

Neurological deterioration after head trauma must be evaluated for possible intracranial injury, even when the initial examination or CT was reassuring.

Conclusion: Diagnosis, Imaging and Recovery After Concussion

Concussion is a mild traumatic brain injury characterized by an acute disturbance of brain function.

The diagnosis is primarily clinical, and conventional CT or MRI may remain normal. Imaging becomes particularly important when associated traumatic intracranial injury is suspected.

The main clinical tasks are to recognize concussion, identify structural injuries when present, monitor neurological recovery, and investigate symptoms that do not improve as expected.

Most patients recover within weeks. Those with persistent symptoms benefit from assessment directed toward the neurological, cervical, vestibular, and other mechanisms responsible for their complaints.