A concussion, also known as a mild traumatic brain injury (mTBI), occurs when a jolt or blow to the head or body causes the brain to move rapidly inside the skull. This sudden movement can stretch and damage brain cells, leading to temporary disruption of normal brain function. Understanding the role of brain scans in assessing concussions is important for anyone who has experienced a head injury.
When Brain Scans Are Used for Concussions
Brain scans are primarily used in the acute phase of a head injury to identify more severe conditions rather than to diagnose a concussion itself. Conditions such as bleeding within the brain (intracranial hemorrhage), skull fractures, or significant brain swelling are serious and require immediate medical attention. A CT scan is a standard tool for assessing the brain right after an injury in adults to detect such issues.
Concussions are functional injuries, meaning they disrupt how the brain works rather than causing large-scale structural damage visible on routine scans. Doctors look for specific “red flags” that might prompt a scan, including severe or worsening headaches, repeated vomiting, seizures, or a deteriorating level of consciousness. These symptoms suggest a possible underlying injury that a scan could detect. If no such indicators are present and clinical decision rules are not met, a CT scan may be safely avoided.
Common Brain Imaging Techniques
CT Scan (Computed Tomography)
A CT scan uses multiple X-ray images taken from different angles to create cross-sectional views of the brain and skull. This imaging technique is fast and widely available, making it suitable for emergency situations. CT scans are particularly effective at quickly detecting acute structural damage like skull fractures, significant brain swelling, or fresh bleeding within or around the brain. While useful for ruling out severe injuries, CT scans appear normal in cases of mild traumatic brain injury, including concussions.
MRI (Magnetic Resonance Imaging)
An MRI uses powerful magnetic fields and radio waves to generate detailed images of soft tissues, including the brain. This technique provides a more nuanced view of brain structures compared to a CT scan, potentially revealing subtle changes a CT might miss. However, an MRI takes longer to perform than a CT scan. MRI scans can identify white matter damage, microbleeds, or swelling, though they are not the first choice in an acute injury setting unless a CT scan is normal but symptoms persist.
Advanced Imaging
Beyond standard CT and MRI, advanced imaging techniques like functional MRI (fMRI), Diffusion Tensor Imaging (DTI), and Positron Emission Tomography (PET) scans exist. fMRI measures brain activity by detecting changes in blood flow, while DTI examines the movement of water molecules to map white matter pathways and detect microscopic damage to nerve fibers. PET scans can reveal changes in brain chemistry. These advanced methods are primarily research tools and are not routinely used for diagnosing concussions.
What Brain Scans Can and Cannot Reveal
For most concussions, standard CT and MRI scans will appear normal. This is because concussions involve microscopic changes in brain function and communication, which are too subtle for conventional scans to detect.
The limitations of current clinical imaging mean that a “normal” scan does not rule out a concussion. These scans detect macroscopic changes like significant bleeding or swelling, not the subtle functional disturbances characteristic of a concussion. Therefore, a person can have a concussion even if their brain scan shows no visible abnormalities. Imaging research continues to explore ways to visualize these subtle changes, focusing more on brain function than just structure.
Beyond Imaging: Assessing Concussions
The diagnosis of a concussion relies heavily on a thorough clinical assessment by a healthcare professional. There is no single test that definitively diagnoses a concussion. Instead, a combination of factors is considered.
A detailed symptom evaluation is a primary component. The healthcare provider asks about symptoms like headache, dizziness, confusion, memory problems, or sensitivity to light and sound, carefully reviewing their nature and onset. A neurological examination follows, which assesses various aspects of brain function, including vision, hearing, strength, sensation, balance, coordination, and reflexes.
Cognitive assessment involves evaluating thinking skills like memory, concentration, and information processing speed. Simple tests may be administered to gauge these abilities. The healthcare professional then uses all this information, combining the patient’s reported symptoms, findings from the neurological exam, and cognitive assessments, to make a clinical diagnosis of a concussion.