Brain damage is detected through a combination of recognizing symptoms, performing hands-on neurological exams, and using imaging and laboratory tests. The specific approach depends on whether the damage is caused by trauma, oxygen deprivation, stroke, or another condition, but the core process follows a consistent path: observe warning signs, assess brain function at the bedside, then confirm with technology that can visualize the injury itself.
Symptoms That Signal Brain Damage
The earliest clues come from what the person experiences or what others notice. After a head injury, the National Institute of Neurological Disorders and Stroke identifies several symptoms that warrant immediate attention, particularly within the first 24 hours: headache, seizures, blurred or double vision, unequal pupil size, clear fluid draining from the nose or ears, nausea, slurred speech, weakness in the arms or legs or face, and loss of balance.
Cognitive and behavioral changes are equally important. These include confusion, disorientation, trouble remembering or concentrating, changes in sleep patterns, unusual irritability, and decreased consciousness (being hard to wake up). Sensory symptoms like dizziness, ringing in the ears, sensitivity to light or sound, and an unexplained bad taste in the mouth can also point to brain injury. Mood swings, fatigue, anxiety, and depression round out the picture. None of these symptoms alone confirms damage, but clusters of them, especially after a known injury, are strong indicators that something is wrong.
How Infants and Young Children Show Signs
Babies and toddlers can’t describe what they’re feeling, so detection relies entirely on behavioral observation. The CDC lists these red flags in children from birth to age four: crying more than usual and being inconsolable, refusing to nurse or eat, changes in sleeping patterns, not wanting to play, appearing dazed or unusually clumsy, slower speech than normal, and vomiting right after an injury. More temper tantrums, sadness, or a sudden need to be held more often can all signal something deeper than a mood shift.
Danger signs that require emergency care include a child who will not stop crying and cannot be consoled, or who refuses to eat entirely. Because infant brains are still developing, injuries that might cause only mild symptoms in adults can produce more significant damage, making early detection critical.
The Bedside Neurological Exam
Before any imaging, a clinician performs a physical neurological exam to identify where in the brain the damage might be. This involves a series of targeted tests that check the cranial nerves, the pathways running directly from the brain to the face, eyes, and head.
Pupil response is one of the most important checks. A light is shone into each eye in a dimly lit room, and the examiner watches for equal constriction. If one pupil reacts sluggishly or doesn’t react at all, that suggests damage along the nerve pathways controlling that eye. An asymmetry between the two eyes is a particularly concerning sign.
Eye movement is tested by having the person follow a finger moving in an H-shaped pattern while keeping their head still. Any deviation, involuntary eye jerking, or abnormal head posture points to dysfunction in specific cranial nerves. Facial symmetry is assessed by asking the person to smile, puff out their cheeks, raise their eyebrows, and show their teeth. Weakness on one side of the face can localize damage to a particular brain region. Strength testing of the neck and shoulders, checking for drooping or difficulty turning the head against resistance, can also reveal which hemisphere is affected.
The Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is the standard scoring system used to quickly classify how severe a brain injury is. It measures three things: eye opening, verbal response, and motor response. Each is scored independently, and the numbers are added together for a total between 3 and 15.
For eye opening, scores range from 1 (no response) to 4 (eyes open spontaneously). Verbal response ranges from 1 (silent) to 5 (fully oriented and coherent). Motor response ranges from 1 (no movement) to 6 (follows commands normally). A total score of 13 to 15 is classified as mild injury, 9 to 12 as moderate, and 3 to 8 as severe. This scale is used in emergency rooms, ambulances, and sports sidelines to make rapid decisions about how urgently someone needs intervention.
CT Scans vs. MRI
CT scans are typically the first imaging tool used because they’re fast and widely available. They excel at detecting skull fractures, acute bleeding, brain herniation, and midline shifts where the brain is being pushed to one side. In an emergency, a CT scan can reveal life-threatening conditions within minutes.
CT has real limitations, though. It misses subtler forms of damage that can still cause serious long-term problems. Diffuse axonal injury, where nerve fibers throughout the brain are stretched and torn, is largely invisible on CT. So are microbleeds, small non-hemorrhagic lesions, and damage to deeper brain structures like the brainstem.
MRI picks up what CT misses. It consistently outperforms CT in sensitivity for these subtle and deep-seated injuries. In one comparison of pediatric patients, MRI found internal brain lesions in 34% of children with traumatic brain injury compared to just 15% on CT. Among children with abusive head trauma, MRI detected abnormalities in roughly 43% versus 11% on CT. Perhaps most strikingly, MRI revealed abnormalities in six out of eight patients whose CT scans had come back completely normal.
Specialized MRI techniques push sensitivity even further. A method called susceptibility-weighted imaging detected additional hemorrhagic lesions in nearly 30% of cases that were invisible on both standard CT and conventional MRI. Diffusion tensor imaging (DTI) is particularly valuable for diffuse axonal injury, a condition that conventional MRI catches in only about half of confirmed cases. DTI tracks the movement of water along nerve fibers and can reveal damage to connections that other imaging methods simply cannot see.
EEG and Brain Wave Monitoring
An electroencephalogram (EEG) measures electrical activity across the brain’s surface and is used to detect functional disruption rather than structural damage. Different abnormal patterns point to different problems. Diffuse slowing, where brain waves drop into abnormally low frequency ranges, reflects widespread cerebral dysfunction. A pattern called alpha coma, where a specific type of wave activity appears across the entire brain, strongly suggests severe brain dysfunction.
Focal abnormalities, where unusual activity concentrates in one area, can indicate a localized structural lesion. Lateralized periodic discharges, repetitive signals firing at regular intervals from one spot, are associated with acute focal damage. A burst suppression pattern, where bursts of activity alternate with periods of near-silence, is seen in the most severe forms of brain injury. EEG is especially useful when imaging looks normal but the person isn’t functioning normally, or when continuous monitoring is needed to track whether the brain is recovering or deteriorating over time.
Blood Tests for Brain Injury
A newer approach uses blood-based biomarkers, proteins released into the bloodstream when brain cells are damaged. The FDA has cleared a point-of-care blood test that measures two proteins: GFAP (released from support cells in the brain) and UCH-L1 (released from neurons). The test is designed to help determine whether a person with a suspected head injury needs a CT scan.
In clinical testing, this blood test correctly identified 96.5% of patients who had positive CT findings, giving it high sensitivity for ruling out the need for further imaging when results come back normal. Its specificity is lower at 40.3%, meaning it flags many people who turn out not to have CT-visible injuries. That tradeoff is intentional: the test is designed to err on the side of caution, catching nearly every significant injury even if it sends some extra people for imaging.
For newborns with suspected oxygen deprivation injuries, researchers are studying additional blood markers. Elevated levels of certain inflammatory proteins and a brain-specific protein called S100B in umbilical cord blood have been linked to the severity of injury and the risk of long-term developmental problems. These biomarkers are not yet standard diagnostic tools, but they represent a shift toward detecting brain damage through a simple blood draw rather than relying solely on imaging.
Sports Concussion Assessment
Concussions in athletes are detected using a structured sideline tool called SCAT (Sport Concussion Assessment Tool), now in its sixth version. It combines multiple evaluation methods into a single protocol: a graded symptom checklist, a standardized cognitive assessment covering memory and concentration, the Glasgow Coma Scale, balance testing using the Balance Error Scoring System, timed tandem gait tests (walking heel-to-toe at various speeds), and a vestibular-ocular motor screening that checks how well the eyes and balance system work together.
The latest version also includes a 15-word list learning task to test short-term memory, observational signs visible to the examiner, and a reading ability screen. Having a pre-season baseline for each athlete makes these assessments far more useful, since the examiner can compare current performance to the person’s own normal rather than relying on population averages. The tool is designed for use by medical professionals, not coaches or parents, because interpreting the results requires clinical judgment about which combination of findings truly indicates a concussion.