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Brain Injury Mechanisms in Car Accidents

Traumatic brain injuries can occur in car accidents in a number of different ways. For example, the head may collide with the airbag or be pierced by a projectile. It is possible for other bodily injuries to lead to brain damage, such as a broken trachea that deprives the brain of oxygen. This article discusses the different mechanisms of brain injury in car accidents and their effects on the brain.

Coup-contrecoup Injury

Coup-contrecoup is a term used to describe a particular mechanism of brain injury in whiplash and similar traumatic scenarios. When the head whips back and forth and/or collides with an object, the brain moves inside the skull. This causes the brain to collide with the skull.

“Coup” refers to the side of first impact and “contrecoup” refers to the side opposite the initial impact. “Coup-contrecoup” is when the brain strikes both the side of the skull on the side of impact, rebounds, and strikes again on the opposite side.

Coup-contrecoup, and more broadly the movement of the brain within the skull during a traumatic event, is the cause of several injuries which are described below, including concussions, contusions, hemorrhages, and hematomas.


Concussions happen when a jolt or blow causes the brain to move rapidly back and forth inside the skull, a coup-contrecoup injury. The brain collides with the interior of the skull, resulting in damage to brain cells and altering brain chemistry. You may hear doctors refer to a concussion as a mild traumatic brain injury (mTBI).

If after a car accident a person exhibits a loss of consciousness, amnesia, confusion, problems with balance, a glazed look in the eye, vomiting, or inappropriate laughing/crying, they may have a concussion.

Symptoms of concussions include:

  • Headache and dizziness
  • Nausea
  • Sensitivity to light and noise
  • Difficulty with mental tasks
  • Sleeping more or less than normal
  • Anxiety, depression, and panic attacks

There is no medication or surgery for concussions—the best way to treat a concussion is to rest from all activities. Though most concussion symptoms go away within a few days to a month, symptoms persist in some people for multiple months or even years. This is known as post-concussion syndrome. It often happens when there is more than one concussion, but it can happen after just one. Being in a motor vehicle collision or bike accident is among the predictors of post-concussion syndrome.


A lesion is any abnormally functioning or damaged area of tissue. Contusions, hemorrhages, and hematomas are all types of brain lesions characterized by bleeding within or around the brain. In car accidents, they are caused by a direct blow to the head which causes coup-contrecoup impact.

A cerebral contusion is essentially a bruise on the brain caused by broken blood vessels. The bruise is accompanied by edema, or swelling. Contusions are found most commonly on the frontal (front) or temporal (mid-lower) lobes. They may also progress into a hemorrhage or co-occur with a hematoma.

Hemorrhage is related to contusions in that it is bleeding within brain tissue. The difference between the two conditions, put simply, is that a hemorrhage involves more bleeding and is even more dangerous. Two types of hemorrhage may result from trauma. An intracerebral hemorrhage is bleeding within the brain. A subarachnoid hemorrhage, usually the result of a less serious injury, is when there is bleeding in the subarachnoid space, one of the layers that lines the brain.

Finally, a hematoma is a blood clot. A pooled collection of blood forms when blood vessels rupture. Hematomas can be epidural (between the skull and the outer layer of the brain), subdural (within the outer layers of the brain), or, more rarely, intracerebral (within the brain).

Cerebral contusions, hemorrhages, and hematomas are serious injuries that follow severe car accidents. The patient will likely be unconscious and diagnosed with a CT scan. Surgery is usually needed to remove the lesion in order to relieve pressure on the brain. Pressure causes brain damage because it squeezes and compresses blood vessels, cutting off the flow of blood and oxygen to brain cells.

Penetration and Skull Fractures

A brain injury from a projectile piercing the skull and brain tissue is a less common but of course serious type of injury. This can happen in car accidents when pieces of the vehicles or objects inside the vehicle are sent flying. The penetrating object can be an object or a fragment of the skull that gets pushed into the brain.

Additionally, multiple types of skull fractures can happen in car crashes:

  • Linear—Most common and least serious type of skull fracture, the bone breaks but does not shift
  • Diastatic—Fracture follows the suture lines of the skull, more often seen in infants
  • Depressed—The skull is collapsed inwards, may need surgery
  • Basilar—The most serious type of skull fracture, the base of the skull breaks

The complications that arise from penetrating head injuries and skull factors are similar to those arising from contusions, hemorrhages, and hematomas. Doctors need to remove the object, skull fragments, and lesions from the brain to remove the pressure. The difference is that open wounds cause blood loss and carry a higher risk of infection.

Diffuse Injuries

Diffuse brain injuries are harder to see than the injuries described above. They are not swollen clots of blood or broken bones. Instead, these injuries are microscopic alterations of the brain whose effects are felt throughout the brain.

In a diffuse-axonal injury, axons are lost. Axons are the string-like parts of the nerves that connect nerves to one another. When brain cells cannot communicate with one another, a person’s neurological function may be severely impaired. During a car crash, the axons are torn as the brain shifts violently within the skull.

Additionally, an anoxic brain injury, also known as ischemia, is when blood supply and oxygen is partially or entirely cut off to an area of the brain. Brain lesions can cause an anoxic brain injury because the lesion puts pressure on blood vessels, constricting them. These injuries can also be caused by a seemingly unrelated injury. A punctured lung or broken trachea, for example, can prevent a person from breathing. Extreme blood loss is another way the body may become oxygen-deprived.

Relevant Accident Brain Injury Studies

Our firm has handled a large number of brain injury car accident cases.  These are some of the studies that can be important in this type of litigation.

Frequency of Primary Neck Pain in Mild Traumatic Brain Injury/Concussion Patients by Jeffrey King et al., Archives of Physical Medicine and Rehabilitation, Jan. 2020.

The authors looked at patients in a trauma center who had a mild TBI and who reported neck pain. Around half of all patients who came in with an mTBI reported neck pain. Pain is more common after motor vehicle accidents than any other cause of injury.

Sleep/Wake Disturbances in Mild Traumatic Brain Injury Patients by Joseph Krainin et al., Traumatic Brain Injury, Nov. 2019.

Changes to a patient’s sleep cycle is a well-established symptom of concussions. The authors of this study assert that mild traumatic brain injury is associated with sleep disorders. Additionally, they claim that using measures of sleep cycle disturbance can help doctors develop better treatment plans for concussion patients.

Characteristics of pedestrian head injuries observed from real world collision data by Guibing Li et al., Accident Analysis & Prevention, Aug. 2019.

Head injury is common in pedestrian car accidents. Using data from Germany, the authors found that skull fractures, focal brain injuries, and concussions are the most common. Also, they note that when the head hits the windshield, concussions are less likely when the leading bonnet edge (hood) is higher.

The polytrauma clinical triad in patients with chronic pain after motor vehicle collision by Cayden Peixoto et al., Journal of Pain Research, Sep. 2018.

The polytrauma clinical triad is the combination of chronic pain, PTSD, and post-concussion syndrome. Of the patients the researchers looked at, who all had chronic pain after being in a car crash, more than half also had PTSD and post-concussion syndrome.

Accident analysis to support the development of strategies for the prevention of brain injuries in car crashes by Jacobo Antona-Makoshi et al., Accident Analysis & Prevention, Aug. 2018.

Light vehicle crash data from the US. National Automotive Sampling System – Crashworthiness Data System was used to estimate the frequency and risk for mild to severe TBIs. Occupants using seatbelts were less at risk. Females using seatbelts were more likely than males to get a concussion in the same circumstances. Additionally, the elderly were much more at risk for subdural hemorrhages.

Mechanisms of Head and Neck Injuries Sustained by Motorcyclists in Fatal Read-World Crashes: Analysis of 47 In-Depth Cases by Thomas Whyte et al., Journal of Neurotrauma, Oct. 2016.

The authors of this study looked at the mechanisms that caused fatal head trauma in motorcycle accidents. They found that motorcycle helmet designs protected against skull fractures but could do better to protect riders from facial trauma and other commonly observed fatal injuries.