Types of brain damage resulting from traumatic brain injury (TBI)

Traumatic brain injury (TBI) is a serious public health problem in many parts of the world including the United States and it costs the government almost 56 billion dollars each year to provide health services towards TBI victims. According to the Center for Disease Control (CDC), out of 1.7 million people undergoing TBIs annually, around 50,000 will succumb to their injuries while a significant number will be added to the growing list of over 5 million Americans requiring long-term post-TBI care. Many those who recover from such injuries may also experience long-term effects including cognitive impairment.

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What is traumatic brain injury?

Although there are numerous definitions explaining a TBI, any such definition should contain several unique characteristics. These include,

  • non-inherited and non-degenerative in nature,
  • caused by an external mechanical force,
  • impairment can be either temporary or permanent,
  • can affect all aspects of brain function including, cognitive, physical, and psychosocial aspects,
  • usually associated with diminished or altered state of consciousness.

What causes a TBI?

In simple terms, a ‘bump’, a ‘jolt’ or a ‘blow’ can lead to a TBI along with any type of penetrating injury. However, CDC explains that, not all ‘bumps’ and ‘jolts’ would cause TBI although an associated loss of consciousness may increase the possibility. According to the National Institute of Neurological Disorders and Stroke, 50% of all TBIs are due to transportation accidents whereas ‘falls’ would be the main cause in the elderly age group. Unfortunately, violence such as assaults and child abuse plays a role in over 20% of TBIs whereas ‘sports related injuries’ accounts for about 3% of such injury.

What is the injury types associated with TBI?

According to literature, TBIs can be classified as injuries occurring at the time of impact, which is also known as ‘primary injuries’ or as ‘secondary injuries’ which refers to subsequent complications usually occurring after several days from the initial incident.

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Primary injuries

Skull fractures, contusions, hematomas, lacerations, diffuse axonal injuries, and penetrating injuries can be classified as primary injuries.

Skull fractures

A skull fracture can result from traumatic forces which exceeds the tensile strength tolerated by the skull bone. When the fracture does not allow communication between inside and the outside environments of the skull, it is termed as a ‘closed fracture’ whereas a fracture exposing the brain tissues to the outside environment is termed as a ‘open’ fracture. It can be further classified as ‘depressed’ or ‘nondepressed’ skull fractures depending on the inward displacement of the fractured segment. Due to the enormous amount of force exerted on the brain during a skull fracture, they can be associated with injuries of the underlying structures, which includes, contusions, nerve damage and hematoma formation.

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Contusions

Contusions of the brain refer to an injury in which a segment of tissues on the brain surface becomes edematous and blood stained due to a significant impact with the skull bone. It may associate with skull fractures or else may present without any such damage at all. When the impact and the injury occur on the same site, it is known as a ‘coup’ injury whereas when the contusion takes place in the opposite side of the impact, it is known as ‘contrecoup’ injury.

Intracranial hemorrhages

As the name suggest, when bleeding takes place within the skull bone, the condition is known as an ‘intracranial hemorrhage’. Bleeding can take place in several sites within the brain and in any of these instances, the underlying cause would be damage to a large blood vessel. Thus, when the bleeding takes place just underneath the skull, it is given the name ‘extra dural’ while bleeding taking place between the outside covering ‘dural membrane’ and the ‘arachnoid membrane’ is known as ‘sub-dural hemorrhage’. When the bleeding takes place between the ‘arachnoid membrane’ and the inner most membrane of the brain, it is given the name, ‘sub-arachnoid’ hemorrhage. Lastly, if the bleeding takes place within the brain tissue, the term ‘intra-cranial’ hemorrhage can be used.

Diffuse axonal injuries

This is an injury, which relates to the deep structures of the brain and one such variation would be the sudden loss of consciousness following a trauma or in other words, a ‘concussion’. Although concussions are considered to be a milder form of diffuse axonal injury, the effects of such injuries would be widespread than the other types of injuries which are mostly localized.

Secondary injuries

Following the initial brain injury, there are several complications, which may arise as secondary events. These may appear slowly and could take several days before it manifest. Among the injury types belonging to secondary injuries, cerebral oedema, brain herniation, hydrocephalus or fluid buildup within the ventricular system of the brain, and increased intracranial pressure can be highlighted. Such injuries can lead to further tissue damage and brain cell death, which can further aggravate the patients existing condition.

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