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CNS Trauma |
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Head injury is one of the most common causes
of disability and death in young men, mainly sustained during road traffic
accidents and falls. Injury is divided into two types:
• Non-missile trauma (closed head injury) is the result of
acceleration/deceleration forces to the head.
• Missile trauma (open head injury) is caused by penetration of the skull or
brain by an external object such as a bullet.
Brain pathology from head injury may be divided into two groups: primary or
secondary
Brain pathology from head injury may be primary (i.e. the immediate consequence
of impact damage) or secondary (i.e. occurring later from brain swelling,
bleeding and hypoxia).
There are two main patterns of primary brain damage in non-missile head injury,
cerebral contusions and diffuse axonal injury.
Cerebral contusions occur when the brain moves within the cranial cavity,
causing parts of the brain to be crushed by violent contact with the skull or
dural membranes. For the most part, these occur adjacent to the site of impact
(coup lesions) and diagonally opposite (contrecoup lesions).
The most common
sites for this pattern of damage are the underside of the frontal lobes, the
tips and inferior aspects of the temporal lobes, the occipital poles, and the
cerebellum.
Early contusions appear as petechial haemorrhage into cortical grey
matter and underlying white matter.
Over a period of several hours there is
oozing of blood, and contusions become haemorrhagic, with severe swelling of the
brain. Severe contusions may be associated with extensive intracerebral, sub-arachnoid
and sub-dural haemorrhage. Contusions heal by gliosis, which is associated with
brown haemosiderin deposition (caused by associated haemorrhage).
Diffuse axonal injury is the result of shearing of axons due to
acceleration/deceleration/torsional forces, leading to severe damage to white
matter tracts. Patients with this pattern of damage who survive are generally
severely disabled. Most of the changes are seen histologically only, consisting
of axonal tearing visible as swellings of the torn ends of nerve fibres (axonal
retraction balls). Petechial haemorrhages may also occur in the corpus callosum
and brain stem, and their detection at these sites is a useful indicator of this
type of severe head injury.
Secondary brain damage occurs after the immediate impact. Head injury is often
associated with widespread trauma, which leads to problems maintaining blood
oxygenation and blood pressure. As a consequence, head injury is often
complicated by the development of secondary hypoxic brain damage and cerebral
oedema.
TRAUMATIC HAEMORRHAGE
Tearing of blood vessels with trauma leads to four main types of cerebral
haemorrhage: intracerebral haematoma, caused by tearing of vessels within the
brain parenchyma; sub-arachnoid haemorrhage, caused by tearing of vessels
adjacent to the sub-arachnoid space; sub-dural haemorrhage, caused by tearing of
veins (discussed below); and extradural haemorrhage, caused by tearing of
vessels in the skull.
Extradural haemorrhage is caused by tearing of vessels running outside the dura
Extradural haemorrhage causes a haematoma in the potential extradural space
between the skull and the dura and is almost always the result of skull
fracture, which tears an artery or a main venous sinus running outside the dura.
The vessel most commonly involved is the middle meningeal artery (associated
with fracture of the temporal bone).
The extradural haematoma appears as a gelatinous layer of blood clot outside the
dura.
This accumulation causes compression of the brain and development of transtentorial herniation. In many cases, high-pressure arterial blood
accumulates rapidly, leading to an acute decline in conscious level with raised
intracranial pressure. In other cases, blood accumulates over a period of hours
and it is not uncommon to have a history of head trauma followed by gradual
development of drowsiness, leading to coma and death.
Some sub-dural haematomas are caused by minor head trauma and have a chronic
evolution pattern.
Sub-dural haemorrhage results in a haematoma developing in the sub-dural space
between the dura and the arachnoid. It is caused by traumatic tearing of venous
vessels that traverse the sub-dural space. Two patterns exist.
Acute sub-dural haematomas are usually seen after a severe head injury and are
associated with other types of brain injury. They cause rapid accumulation of
blood, leading to acute neurological deterioration as a result of raised
intracranial pressure.
Chronic sub-dural haematomas usually occur as a result of minimal trauma and are
mainly seen in the very young (including childhood non-accidental injury) and
the elderly. Blood typically accumulates slowly over a period of days or weeks,
becoming localized by a membrane of fibrovascular granulation tissue. In
addition to the osmotic effects of degenerating blood clot drawing in fluid from
the CSF, increase in the size of the haematoma occurs with further bleeding.
Clinical symptoms and signs may only become obvious weeks after an apparently
trivial injury, as a result of raised intracranial pressure.
Macroscopically a sub-dural haematoma is seen as a layer of gelatinous blood
clot (acute type) or as an organized layer of dark liquefied clot surrounded by
membranes (chronic type), which flattens and compresses the underlying brain,
staining the outside of the arachnoid with haemosiderin.
Trauma to the spinal cord is a common cause of disability in young men
Most spinal cord injuries occur in young males as a result of road traffic
accidents, falls and sport.
Injury is mainly caused by fracture and dislocation of the vertebral column,
causing compression of the spinal cord by distortion of the spinal canal. Minor
contusions of the cord result in transient recoverable neurological abnormality.
Severe contusions cause damage to ascending and descending tracts, as well as
necrosis of neurons at the segments damaged.
The consequence of cord damage depends on the spinal level of the injury;
cervical lesions cause tetraplegia, whereas lower thoracic lesions cause
paraplegia. Denervated muscles undergo atrophy, with secondary contractures and
deformities in limbs. Denervation of the bladder leads to problems with
micturition, urinary stasis and recurrent infections.
Penetrating injuries of the spinal cord are uncommon, but may be seen after
stabbings or shootings. Complete transection of the cord may occur, hemisection
giving rise to a Brown-Séquard syndrome.
In addition to trauma, the spinal cord and nerve roots are vulnerable to damage
by non-traumatic compression. |
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