A concussion is classified as a mild Traumatic Brain Injury (mTBI). It is a temporary functional disturbance affecting how the brain operates, often resulting from a sudden blow or jolt to the head or body. While symptoms like confusion, headache, and dizziness can be significant, the injury itself does not usually involve visible physical damage to the brain structure. For this reason, a Computed Tomography (CT) scan is generally not used to establish a concussion diagnosis. The scan serves a distinctly different, though equally important, purpose in the initial evaluation of head trauma.
What a CT Scan Detects
The primary role of a CT scan in a head injury is to quickly rule out immediate, life-threatening structural issues. This imaging technology uses specialized X-rays to create cross-sectional images, visualizing differences in tissue density within the skull. The resulting images are highly effective at identifying acute pathology that requires urgent intervention.
The scan detects significant complications such as intracranial hemorrhage (bleeding within the skull). This includes epidural or subdural hematomas, where blood pools between the brain and its protective outer layers. Rapid identification of these bleeds allows medical teams to determine if immediate neurosurgery or intensive critical care is necessary.
Furthermore, a CT scan can identify skull fractures and significant cerebral edema, or swelling of the brain tissue. These structural findings represent physical changes in the anatomy that are clearly visible due to the dense contrast they provide against normal brain matter. Therefore, the scan functions mainly as an emergency triage tool, rather than a diagnostic tool for the functional disturbance of a concussion.
Why CT Scans Miss Concussions
The fundamental reason a CT scan cannot detect a concussion lies in the nature of the injury itself. Concussions are functional injuries; they disrupt the brain’s normal cellular processes without causing gross anatomical damage visible to standard imaging. The technology relies on visualizing differences in density (bone, fluid, or large blood clots), but it is unable to register changes at the microscopic level.
Following a concussive event, the brain undergoes a cascade of microscopic and metabolic changes at the cellular level. These changes include massive, unregulated shifts of ions, such as potassium leaving the cell and calcium entering. This forces the cell to expend enormous amounts of energy to restore balance, a phenomenon often described as an “energy crisis” in the brain.
This intricate disruption involves temporary abnormalities in neurotransmitter release and glucose metabolism, but these chemical and electrical disturbances do not alter the physical structure or density of the brain tissue. Because the CT scan only detects macroscopic structural changes, it cannot capture these subtle, temporary functional impairments. The injury is essentially invisible to the technology.
Clinical Assessment and Concussion Diagnosis
When a CT scan comes back negative, it provides reassurance that no immediate, life-threatening structural injury exists, but it does not mean the patient is uninjured. The diagnosis of a concussion relies entirely on a comprehensive clinical assessment performed by a trained healthcare professional. This process focuses on observing and documenting the functional symptoms and impairments experienced by the patient.
The clinician begins by gathering a detailed history of the injury and the patient’s current symptom profile, which may include headache, nausea, sensitivity to light or noise, and feelings of fogginess or confusion. Standardized assessment tools, such as the Sport Concussion Assessment Tool 5 (SCAT5) or similar checklists, are used to systematically quantify the severity and type of symptoms reported. These tools provide a baseline for monitoring recovery.
The assessment also includes a focused neurological examination designed to test brain functions. This typically involves evaluating the patient’s orientation to time, place, and person, as well as testing short-term memory, balance, coordination, and reaction time. Abnormalities in these areas are direct evidence of the functional disturbance caused by the concussion.
Ultimately, the diagnosis is clinical, established by correlating the mechanism of injury with the presence of new or worsening symptoms and observable neurological deficits. The negative CT scan confirms that the medical path forward should focus on managing the functional injury rather than treating a structural emergency.