Focal and diffuse brain injury are ways to classify brain injury

Brain injury

A brain injury is any injury occurring in the brain of a living organism. Brain injuries can be classified along several dimensions. Primary and secondary brain injury are ways to classify the injury processes that occur in brain injury, while focal and diffuse brain injury are ways to classify...

: focal injury occurs in a specific location, while diffuse injury occurs over a more widespread area. It is common for both focal and diffuse damage to occur as the result of the same event; many traumatic brain injuries have aspects of both focal and diffuse injury. Focal injuries are commonly associated with an injury in which the head strikes or is struck by an object; diffuse injuries are more often found in acceleration

Acceleration

In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

/deceleration injuries, in which the head does not necessarily contact anything, but brain tissue is damaged because tissue types with varying densities accelerate at different rates. In addition to physical trauma

Physical trauma

Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

, other types of brain injury

Acquired brain injury

An acquired brain injury is brain damage caused by events after birth, rather than as part of a genetic or congenital disorder such as fetal alcohol syndrome, perinatal illness or perinatal hypoxia. ABI can result in cognitive, physical, emotional, or behavioural impairments that lead to permanent...

, such as stroke

Stroke

A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

, can also produce focal and diffuse injuries. There may be primary and secondary brain injury

Primary and secondary brain injury

Primary and secondary brain injury are ways to classify the injury processes that occur in brain injury. In traumatic brain injury , primary injury occurs during the initial insult, and results from displacement of the physical structures of the brain. On the other hand, secondary injury occurs...

 processes.

Focal

A focal traumatic injury results from direct mechanical forces (such as occur when the head strikes a windshield in a vehicle accident) and is usually associated with brain tissue damage visible to the naked eye. A common cause of focal injury is penetrating head injury

Penetrating head injury

A penetrating head injury, or open 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...

, in which the skull is perforated, as frequently occurs in auto accidents, blows, and gunshot wounds. Focal injuries typically have symptoms that are related to the damaged area of the brain. Stroke can produce focal damage that is associated with signs and symptoms that correspond to the part of the brain that was damaged. For example, if a speech center of the brain such as Broca's area

Broca's area

Broca's area is a region of the hominid brain with functions linked to speech production.The production of language has been linked to the Broca’s area since Pierre Paul Broca reported impairments in two patients. They had lost the ability to speak after injury to the posterior inferior frontal...

 is damaged, problems with speech are common.

Focal injuries include the following:

• Cerebral contusion
  Cerebral contusion
  Cerebral contusion, Latin contusio cerebri, a form of traumatic brain injury, is a bruise of the brain tissue. Like bruises in other tissues, cerebral contusion can be associated with multiple microhemorrhages, small blood vessel leaks into brain tissue. Contusion occurs in 20–30% of severe head...
  
   is a bruise of brain tissue that commonly results from contact of the brain with the inside of the skull.
• Cerebral laceration
  Cerebral laceration
  A cerebral laceration is a type of traumatic brain injury that occurs when the tissue of the brain is mechanically cut or torn. The injury is similar to a cerebral contusion; however, according to their respective definitions, the pia-arachnoid membranes are torn over the site of injury in...
  
   is a brain injury in which the pia
  Pia mater
  Pia mater often referred to as simply the pia, is the delicate innermost layer of the meninges, the membranes surrounding the brain and spinal cord. The word finds its roots in Latin, meaning literally "tender mother." The other two meningeal membranes are the dura mater and the arachnoid mater....
  
  -arachnoid
  Arachnoid mater
  The arachnoid mater, literally from Latin "spider -like mother", is one of the three meninges, the membranes that cover the brain and spinal cord...
  
   is torn.
• Epidural hemorrhage is bleeding between the dura mater
  Dura mater
  The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
  
   and the skull. It is commonly associated with damage to the middle meningeal artery
  Middle meningeal artery
  The middle meningeal artery is typically the third branch of the first part of the maxillary artery, one of the two terminal branches of the external carotid artery...
  
  , often resulting from a skull fracture
  Skull fracture
  A skull fracture is a break in one or more of the bones in the skull usually occurring as a result of blunt force trauma. If the force of the impact is excessive the bone may fracture at or near the site of the impact...
  
  .
• Subdural hemorrhage is bleeding between the dura mater and the arachnoid.
• Intracerebral hemorrhage is bleeding within the brain tissue itself.
• Intraventricular hemorrhage
  Intraventricular hemorrhage
  An intraventricular hemorrhage , often abbreviated "IVH," is a bleeding into the brain's ventricular system, where the cerebrospinal fluid is produced and circulates through towards the subarachnoid space...
  
   is bleeding within the ventricle
  Ventricular system
  The ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord.-Components:The system comprises four ventricles:* right and left lateral ventricles* third ventricle...
  
  s of the brain.

Diffuse

Diffuse injuries, also called multifocal injuries, include brain injury due to hypoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

, meningitis

Meningitis

Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...

, and damage to blood vessel

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

s. Unlike focal injuries, which are usually easy to detect using imaging, diffuse injuries may be difficult to detect and define; often, much of the damage is microscopic

Microscope

A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...

. Diffuse injuries can result from acceleration/deceleration injuries. Rotational forces are a common cause of diffuse injuries; these forces are common in diffuse injuries such as concussion and diffuse axonal injury

Diffuse axonal injury

Diffuse axonal injury is one of the most common and devastating types of traumatic brain injury, meaning that damage occurs over a more widespread area than in focal brain injury. DAI, which refers to extensive lesions in white matter tracts, is one of the major causes of unconsciousness and...

. The term "diffuse" has been called a misnomer, since injury is often actually multifocal, with multiple locations of injury.

Diffuse injuries include the following:

• Diffuse axonal injury
  Diffuse axonal injury
  Diffuse axonal injury is one of the most common and devastating types of traumatic brain injury, meaning that damage occurs over a more widespread area than in focal brain injury. DAI, which refers to extensive lesions in white matter tracts, is one of the major causes of unconsciousness and...
  
   is widespread damage to the white matter
  White matter
  White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
  
   of the brain that usually results from acceleration/deceleration types of injury.
• Ischemic brain injury resulting from an insufficient blood supply to the brain, is one of the leading causes of secondary brain damage after head trauma.
• Vascular injury usually causes death shortly after an injury. Although it is diffuse type of brain injury itself, diffuse vascular injury is generally more likely to be caused by focal than diffuse injury.
• Swelling, commonly seen after TBI, can lead to dangerous increases in intracranial pressure
  Intracranial pressure
  Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
  
  . Though swelling itself is a diffuse type of injury, it can result from either focal or diffuse injury.