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About Brain Injury

Understanding Brain Injury

Brain injuries may be classified as traumatic or non-traumatic to describe the cause of the injury. They may also be classified as mild, moderate, or severe to indicate the initial severity of the injury. Other terms, such as diffuse or penetrating, may be used to describe the type injury. The most commonly used terms are shown below:

Diffuse Axonal Injury

A diffuse axonal injury can be caused by shaking or strong rotation of the head, as with shaken baby syndrome, or by rotational forces, such as with a car accident.

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  • Injury occurs because the unmoving brain lags behind the movement of the skull, causing brain structures to tear.
  • There is extensive tearing of nerve tissue throughout the brain. This can cause brain chemicals to be released, causing additional injury.
  • The tearing of the nerve tissue disrupts the brain’s regular communication and chemical processes.
  • This disturbance in the brain can produce temporary or permanent widespread brain damage, coma, or death.
  • A person with a diffuse axonal injury could present a variety of functional impairments depending on where the shearing (tears) occurred in the brain.

Concussion/Mild Traumatic Brain Injury (mTBI)

A concussion can be caused by direct blows to the head, gunshot wounds, violent shaking of the head, or force from a whiplash-type injury. Both closed and open head injuries can produce a concussion. A concussion is the most common type of traumatic brain injury.

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  • A concussion is caused when the brain receives trauma from an impact or a sudden momentum or movement change. The blood vessels in the brain may stretch and cranial nerves may be damaged.
  • A person may or may not experience a brief loss of consciousness (not exceeding 20 minutes). A person may remain conscious, but feel “dazed” or “punch drunk”.
  • A concussion may or may not show up on a diagnostic imaging test, such as a CAT scan.
  • Skull fracture, brain bleeding, or swelling may or may not be present.
  • A concussion can cause injury resulting in permanent or temporary damage.
  • It may take a few months to a few years for a concussion to heal.


A contusion is a bruise (bleeding) on the brain caused by a force (blow or jolt) to the head.

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  • A contusion can be the result of a direct impact to the head.
  • Large contusions may need to be surgically removed.

Coup-Contrecoup Injury

Coup-contrecoup injury describes contusions that are both at the site of the impact and on the complete opposite side of the brain. This occurs when the force impacting the head is not only great enough to cause a contusion at the site of impact, but is also able to move the brain and cause it to slam into the opposite side of the skull.

Second Impact Syndrome

Second impact syndrome, also termed “recurrent traumatic brain injury,” can occur when a person sustains a second traumatic brain injury before the symptoms of the first traumatic brain injury have healed. The second injury may occur from days to weeks following the first. Loss of consciousness is not required. The second impact is more likely to cause brain swelling and widespread damage.

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Because death can occur rapidly, emergency medical treatment is needed as soon as possible.
The long-term effects of recurrent brain injury can be muscle spasms, increased muscle tone, rapidly changing emotions, hallucinations, and difficulty thinking and learning.

Penetrating Injury

Penetrating injury to the brain occurs from the impact of a bullet, knife, or other sharp object that forces hair, skin, bone, and fragments from the object into the brain.

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  • Objects traveling at a low rate of speed through the skull and brain can ricochet within the skull, which widens the area of damage.
  • A “through-and-through” injury occurs when an object enters the skull, goes through the brain, and exits the skull. Through-and-through traumatic brain injuries include the effects of penetration injuries, plus additional shearing, stretching, and rupture of brain tissue.
  • Firearms are the single largest cause of death from traumatic brain injury.

Abusive Head Trauma (Shaken Baby Syndrome)

Abusive head trauma, also known as shaken baby syndrome, is a violent criminal act that causes traumatic brain injury. Abusive head trauma occurs when the perpetrator aggressively shakes a baby or young child. The forceful whiplash-like motion causes the brain to be injured.

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  • Blood vessels between the brain and skull rupture and bleed.
  • The accumulation of blood causes the brain tissue to compress while the injury causes the brain to swell. This damages the brain cells.
  • Abusive head trauma can cause seizures, lifelong disability, coma, and death.
  • Irritability, changes in eating patterns, tiredness, difficulty breathing, dilated pupils, seizures, and vomiting are signs of abusive head trauma. A baby experiencing such symptoms needs immediate emergency medical attention.

Locked-in Syndrome

Locked-in syndrome is a rare neurological condition in which a person cannot physically move any part of their body aside from their eyes.

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  • The individual is conscious and able to think.
  • Vertical eye movements and eye blinking can be used to communicate with others and operate environmental controls.

Open Head Injury

An open head injury, also known as a penetrating head injury, is a head injury in which the dura mater (the outer layer of the meninges) is breached. Penetrating injury can be caused by high-velocity projectiles or objects of lower velocity such as knives, or bone fragments from a skull fracture that are driven into the brain.

Closed Head Injury

A closed head injury is an injury to the brain caused by an outside force without any penetration of the skull. With a closed head injury, when the brain swells, it has no place to expand. This can cause an increase in intracranial pressure, which is the pressure within the skull.

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As the brain swells, it may expand through any available opening in the skull, including the eye sockets. When the brain expands through the eye sockets, it can compress and impair the functions of the eye nerves. For instance, if an eye nerve, Cranial Nerve III, is compressed, a person’s pupil (the dark center part of the eye) will appear dilated (big). This is one reason why medical personnel may monitor a person’s pupil size and intracranial pressure.

Speak to a Brain Injury Expert

Caring professionals at the National Brain Injury Information Center (NBIIC) are ready to answer your questions.

Dial 1-800-444-6443


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