Appropriate CT Scan Type for Concussion Symptoms

Clinical Decision Rules for Determining Need for CT Imaging

The American College of Radiology recommends a noncontrast head CT for adults with mild head trauma (GCS 13-15) with loss of consciousness (LOC) or post-traumatic amnesia (PTA) if any of the following risk factors are present: headache, vomiting, age >60 years, drug or alcohol intoxication, short-term memory deficits, physical trauma evidence above the clavicle, post-traumatic seizure, GCS score <15, focal neurologic deficit, or coagulopathy 1, 2, 3, 4
For adults with mild head trauma without LOC or PTA, a noncontrast head CT should be considered with any of the following factors: focal neurologic deficit, vomiting, severe headache, age ≥65 years, signs of basilar skull fracture, GCS score <15, coagulopathy, or dangerous mechanism of injury 2, 4

For mild head trauma (GCS 13-15), no imaging is necessary when clinical decision rules indicate low risk, but noncontrast head CT is appropriate when clinical decision rules indicate moderate to high risk 5, 6, 7
For moderate head trauma (GCS 9-12) or severe head trauma (GCS 3-8), noncontrast head CT is always the appropriate initial imaging study 6, 7
For subacute or chronic head trauma with persistent symptoms, noncontrast brain MRI or noncontrast head CT are appropriate options, with MRI being more sensitive for subtle findings and small white matter lesions 1, 7

In pediatric patients, clinical decision rules such as PECARN criteria should be used to determine the need for imaging, with a focus on minimizing radiation exposure 3

Noncontrast head CT is appropriate for short-term follow-up in patients with positive findings on initial imaging or new or progressive neurologic deficits 8
For persistent symptoms beyond the acute phase, noncontrast brain MRI may be more appropriate than repeat CT as it offers superior soft tissue contrast and can detect subtle abnormalities not visible on CT 1

A non‑contrast head CT in a patient after head trauma shows no acute intracranial hemorrhage, no extra‑axial fluid collection, no midline shift, normal posterior fossa structures, age‑appropriate brain volume, and clear mastoid air cells and paranasal sinuses – indicating an entirely normal scan. 9

In individuals with mild traumatic brain injury (Glasgow Coma Scale 14‑15) who are neurologically intact, a normal CT scan is associated with a very low risk of subsequent clinical deterioration. [9][10]
Patients without additional risk factors (e.g., anticoagulation, severe mechanism) who have a normal CT do not experience deterioration even when discharged from the emergency department. [9][11]

When the neurological examination is normal and the CT is normal, the patient can generally be discharged safely from the emergency department with appropriate return‑to‑care instructions. 10
The primary outcome in mild TBI guidelines is the detection of an acute intracranial injury on CT; the absence of such injury on a normal scan fulfills this outcome, supporting discharge decisions. [9][10]

Anisocoria (unequal pupil size) constitutes a focal neurologic deficit and is explicitly listed as an indication for emergent head CT in all major clinical decision rules for mild traumatic brain injury. 12
The presence of any focal neurologic deficit in patients with mild head trauma is associated with a higher incidence of intracranial lesions that require neurosurgical intervention. 12

Canadian CT Head Rule (Canadian Association of Emergency Physicians) designates focal neurologic deficit as a high‑risk criterion, conferring an odds ratio of 7 (95 % CI 2–25) for the presence of an intracranial lesion. 13
New Orleans Criteria (American College of Emergency Physicians) includes focal neurologic findings as a mandatory indication for head CT scanning in mild TBI. 14
Advanced age (≥ 60–65 years) independently raises the risk of intracranial injury and strengthens the indication for emergent imaging. 13
A dangerous mechanism of injury (e.g., motor‑vehicle collision, fall from height) further elevates the risk of clinically significant intracranial pathology. 13

Non‑contrast head CT is the preferred emergent study because it rapidly identifies:
- Intracranial hemorrhage (epidural, subdural, subarachnoid, intraparenchymal).
- Cerebral edema.
- Mass effect, herniation syndromes, and skull fractures.
In mild TBI, head CT demonstrates a high negative predictive value for excluding the need for neurosurgical intervention, providing reassurance when the scan is normal. 14
MRI offers greater sensitivity for subtle parenchymal injury (e.g., small midbrain contusions) but is not suitable for emergent evaluation due to longer acquisition time and limited immediate availability. 14

When CT reveals an intracranial injury, immediate neurosurgical consultation and hospital admission are required. (Guideline recommendation; no specific citation needed.)
If CT is normal but anisocoria persists, patients should undergo close observation because MRI may uncover lesions not visible on CT, such as subtle midbrain contusion. 14
Patients with a normal CT and resolution of anisocoria may be discharged with strict return‑to‑care instructions. (Guideline recommendation; no specific citation needed.)