Approach

Diagnosing mild traumatic brain injury (TBI) is difficult based on acute injury characteristics and presenting signs and symptoms alone. This can be problematic because diagnostic symptoms are nonspecific to concussion, and owing to the subjective nature of symptom reporting; relatively high base rates of mild TBI symptoms are seen in the general non head-injured population, particularly in people who have been exposed to general trauma in the absence of TBI.[50]​ It should be noted that there are no objective aids to the diagnosis of concussion.

Initial history

History for mild TBI is centered on the injury event.

A typical history should begin with establishing how the injury occurred and whether the impact was directly to the head or transmitted to the head by the acceleration-deceleration of the body on impact, corroborated by an observer when possible.[5]​ Somatic, cognitive, and affective symptoms should be enquired about, typically rated on a Likert scale to assess their severity. It is important to note the symptoms that occurred immediately after the injury was sustained, as well as those that are still present at the time of evaluation. A variety of symptom scales are available.[3]​​

It is common for symptoms to worsen the day after injury, especially in patients who have a positive history for mild TBI, including concussion.[51] Previous brain traumas can lower the impact threshold, making mild TBI more likely regardless of the force of impact and, therefore, increasing the chances of future brain trauma.

Alcohol and substance misuse is associated with a significantly higher risk for all forms of TBI, but this is confounded by a higher overall risk for all forms of external injury.[34][35]

Symptoms may fluctuate, but typically subside after a week to a month. Physicians should specifically enquire about the following symptoms:

  • Headache: the most commonly reported symptom.[52][53]​ Although often felt immediately, headache can worsen the day after the injury is sustained. 30% of patients with mild TBI continue to report headache at three months post-trauma.[54] Medication overuse, neck injuries, sleep disturbance and psychological comorbidity may all contribute to headache after mild TBI.[55]

  • Disturbed gait/balance or dizziness: when occurring after a head injury, typically related to benign paroxysmal positional vertigo.[55] These symptoms may be alarming to patients if they do not settle quickly. Explaining that they are due to debris dislodged into the inner ear by the injury can help to alleviate patients’ concerns about "brain damage".[55] Vestibular migraine and depersonalization (a sense of disconnection from the body) are other causes of dizziness in this population. Central vestibular disorders can occur but are more typical after moderate or severe brain injury.[55] See Benign paroxysmal positional vertigo.

  • Mental slowing and fogginess: patients report these as a general feeling, often accompanied by difficulty sustaining attention, and general fatigue.[4][6]​​

  • Memory difficulties: these can be centered on the injury incident itself or generalized to include difficulty in day-to-day situations, and typically co-occur with other cognitive and/or physical symptoms, such as headaches. Memory lapses are common in the general population and are not specific to mild TBI.[55]

  • Vomiting and nausea: less typical in adults, occurring much more frequently in adolescents and children. When vomiting is the only symptom of head injury in a child, TBI on CT is uncommon and clinically important TBI is very uncommon.[56] TBI is more frequent in children when vomiting is accompanied by other signs or symptoms suggestive of TBI.[56]

  • Neck pain: more commonly associated with motor vehicle collisions than with other mechanisms of injury.[57] If present, the patient should be assessed for a cervical spine injury. See Acute cervical spine trauma in adults.

Factors affecting outcome

Factors that prolong recovery should be considered to be modifying factors.[58] Overall, it remains quite difficult to predict which factors will contribute to persistent symptoms.[59] Some risk factors can worsen the outcome and should be enquired about by the physician, including previous brain injury and premorbid psychiatric history.[4][60]​​​ See Prognosis.

Physical exam

Every patient reporting for evaluation after a head injury should undergo a complete physical exam, focussing on examination of the head and neck, and neurologic system. There is generally no observable neurologic sign, and no physical abnormality on physical exam.[61] Postural instability on dynamic motor assessments and slower reaction times have been reported.[62][63][64][65]​ Patients should be examined for a suspected basilar fracture which may present with:

  • Clear fluid (possible cerebrospinal fluid) leaking from the ear(s) or nose

  • Periorbital hematoma(s) with no associated damage around the eyes ("raccoon" ["panda"] eyes)

  • Bleeding from one or both ears, blood behind the eardrum (hemotympanum), new deafness in one or both ears

  • Battle sign - bruising behind one or both ears over the mastoid process, suggesting fracture of the middle cranial fossa. See Skull Fractures.

Examination of the head and neck is important for diagnosing potentially treatable causes of headache, such as temporomandibular joint bruising, dental injuries, or cervical muscle strain. Admission to the hospital (and imaging of the brain) should be considered if the patient has any of the following risk factors:

  • a Glasgow Coma Scale (GCS) score <15, or after imaging, a GCS score that has not returned to 15 or their pre-injury baseline, regardless of the imaging results

  • post-traumatic seizure

  • signs of skull fracture or penetrating injury

  • loss of consciousness[66]

  • severe headache

  • persistent vomiting

  • meningism

  • cerebrospinal fluid leak

  • suspicion of ongoing post-traumatic amnesia

  • a high-risk mechanism of injury (e.g., road traffic accident, significant fall)

  • suspected nonaccidental injury

  • a coagulopathy

  • receiving anticoagulant therapy[67]

  • previous brain surgery

  • current drug or alcohol intoxication

  • shock

  • focal neurologic deficit since the injury.​

Neuropsychological testing

Cognitive symptoms usually resolve quickly after mild TBI; a minority of patients have memory and concentration problems within three months of injury.[55] Neuropsychological testing involves paper-and-pencil or computerized tests assessing attention, memory, and executive functions, as well as reaction times. Routine referral for cognitive (psychometric) assessment is not recommended after mild TBI; careful assessment of the nature of the injury and symptoms, including bedside cognitive tests is more appropriate in the first instance.[55][68][69]​​​ Most guidelines support the use of formal sidelines or office-based cognitive testing for sports-related concussion.[3][5] Cognitive performance can be affected by stress, fatigue, effort, and medications. Therefore, if testing is required, neuropsychological evaluations should be carried out by trained neuropsychologists who can disentangle the effects of these factors from the consequences of mild TBI. Guidelines on sport-related concussion support the use of neuropsychological testing to diagnose the effects of mild TBI, help make return-to-play decisions for athletes, and monitor recovery.[5] It is important to ensure that an appropriate amount of time has passed between testing sessions to guard against practice effects and uphold test validity. Although neuropsychological tests are an important component of mild TBI assessment, they should not be the only benchmark in making decisions about recovery from a mild TBI.[70]

Quick assessment tools

Quick assessment tools can be invaluable, particularly for sideline evaluations. They include:

  • Sport Concussion Assessment Tool (SCAT) SCAT6: sport concussion assessment tool - 6th edition Opens in new window[71]​​ The Child SCAT6 should be used in patients ages 8-12 years.

  • McGill Abbreviated Concussion Evaluation (ACE)[72]

  • various iterations of the ImPACT cognitive test for the assessment of signs and symptoms of head injury (e.g., ImPACT sideline card; ImPACT computerized concussion management tool; ImPACT pediatric computerized concussion management tool).

Regardless of the choice of assessment tool, an assessment of balance and postural stability is essential in the initial evaluation of the concussed athlete.

Brain imaging

In cases with loss of consciousness or impact seizure, patients should receive a comprehensive evaluation for serious brain or cervical spine injury.[4] CT is most commonly used because it rapidly rules out intracranial bleeding or bony injuries. The New Orleans Criteria or the Canadian CT head rule can be used as an assessment guide to imaging.[67][73][74]​​​​

Cases where there are positive imaging results may include prolonged alterations to consciousness, focal neurologic deficits, and worsening symptoms (typically uncontrollable headache, nausea, vomiting, and severe dizziness).[65][67]​​[75]​​​[76]​​​​​ Indications for admission to hospital should also be considered as strong indications to perform diagnostic imaging and include:

  • a Glasgow Coma Scale (GCS) score <15; or, after imaging, a GCS score that has not returned to 15 or the pre-injury baseline, regardless of the imaging results

  • post-traumatic seizure

  • signs of skull fracture or penetrating injury

  • loss of consciousness[66]

  • severe persistent headache

  • persistent vomiting

  • meningism

  • cerebrospinal fluid leak

  • suspicion of ongoing post-traumatic anterograde or retrograde amnesia

  • a high-risk mechanism of injury (e.g., road traffic accident, significant fall)

  • suspected nonaccidental injury

  • a coagulopathy

  • receiving anticoagulant therapy[67]

  • previous brain surgery

  • current drug or alcohol intoxication

  • shock

  • focal neurologic deficit since the injury.​

Do not routinely obtain head CT scans for patients with minor head injury who are at low risk based on validated decision rules.[67]​[77]​​​​ In children, use clinical observation/Pediatric Emergency Care Applied Research Network (PECARN) criteria to determine whether imaging is indicated.[78][79]

Several guidelines recommend, or suggest consideration of, CT head imaging for anticoagulated patients after minor head injury, regardless of symptoms.[67]​​​[80]​​​​​ However, the supporting evidence base is limited.​[80][81]​ If initial CT shows no hemorrhage and no other criteria are met for extended monitoring, routine admission or observation is not indicated after a minor head injury for patients who are taking anticoagulants or antiplatelet medications.[67] 

The absence of CT abnormalities does not exclude structural damage.[2] Avoid ordering a brain MRI to evaluate an acute concussion unless more severe brain injury is suspected.[82]​ Brain MRI should be obtained if there is suspicion of an intracerebral structural lesion or hematoma, and CT scan is negative. Studies report structural traumatic abnormalities on MRI, (performed 2-3 weeks after injury) in approximately 30% of patients with mild TBI who had a normal CT on presentation.[2][26][27]​​​​​​​​​ Advanced MRI techniques, such as diffusion tensor imaging and susceptibility weighted imaging are more sensitive than standard MRI at detecting superficial contusions, traumatic axonal injury and traumatic vascular injury.[2][83][84]​​​​​​​ Fast MRI is feasible and accurate relative to CT in clinically stable children, in whom exposure to ionizing radiation may otherwise be a concern.[85]

The most common structural changes observed are cerebral contusions; less common observations include epidural hematomas, subdural hematomas, and axonal injury.[Figure caption and citation for the preceding image starts]: Sites of contusions and epidural hematomas: (A) prefrontal cortex, (B) pterion, (C) temporal-parietal cortex (often during contre-coup)From the collection of L. Henry; used with permission [Citation ends].com.bmj.content.model.Caption@5cdbfbea

Alternative and emerging imaging modalities

Positron emission tomography (PET), single-photon emission CT [SPECT], magnetic resonance spectroscopy, and diffusion tensor imaging have yielded promising results that provide valuable insights into the pathophysiology of concussion, but are not yet recommended outside of a research setting.[86] It is noteworthy that both PET and SPECT have been used to demonstrate clinical changes in those patients with persistent symptomatology in the form of hypoperfused brain areas.[87][88][89][90]

Newer, advanced multimodal MRI technologies (e.g., diffusion tensor imaging, resting state functional MRI, quantitative susceptibility imaging, magnetic resonance spectrography, and arterial spin labeling) are being studied in research protocols aimed at understanding the neurobiologic effects of, and recovery after, mild TBI.[3]​​

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