Topic 9 - Head Injuries Flashcards
Describe the development of an intracranial haematoma
Following head injury, blood can gather between the meninges or within the brain - no true space in normal anatomy, increases potential space
Describe the ability of the CNS to recover
- CNS neurons have limited ability to recover in comparison to PNS neurons
- Substantial functional recovery occurs due to neural plasticity
- Potential for brain to change structure and function - rewiring of neurons
- Greater exposure to particular stimulis means more neurons are dedicated to that stimulus (+ vice versa)
List the types of brain injuries
- Primary injury - result of initial trauma
- Secondary injury - evolving pathophsysiological consequences of the primary injury
Describe the development of a subdural haematoma
- Venous blood
- Collects between dura and arachnoid mater
- No limitation of blood flow, spreads more evenly
Describe the appearance of a subdural haematoma on a CT
- No limitation of blood flow, blood can spread more evenly
- Less clear on CT, crescent shape
List the clinical signs of displacement of the cingulate gyrus under the falx cerebri
- May have no clinical signs
- May be confused, drowsy or show contralateral weakness
- Pressure on motor cortex or compression of anterior cerebral artery)
When does recovery from brain injuries occur?
Fastest recovery occurs in the first 6 months, continues for 2 years
Describe normal and abnormal flexion in the motor response section of the Glasgow coma scale
Normal - elbow bends, arm moves away from body
Abnormal - elbow bends, arm moves over body
Why does brain herniation develop after head injuries?
Brain is not compressible - as mass expands causes displacement (herniation)
Explain the clinical usefullness of a Glasgow Coma Score
Numbers from each section can be added to give score, not accurate representation of patient’s condition
Describe the appearance of an extradural haematoma on a CT scan
- Characteristic lens shape - blood collects in one area because the dura is fixed to the skull at sutures so it can’t spread
- Causes midline shifting - loss of ventricles
- Fresh blood appears white, turns more grey with time
List the categorisation of GCS scores
Mild = 13-15
Moderate = 9-12
Severe = 8 or less
List types of secondary head injuries
- Cerebral oedema
- Increased intracranial pressure
- Haemorrhage
- Herniation
- Seizures
- Ischaemia
List the behavioural consequences of brain injury
- Period of confusion, disorientation
- Attention and learning ability lost
- Agitation, agression, frustration
- Nervousness, restlessness
- Sleeping pattern disrupted
- Overreaction to stimulation
- Inconsistent behaviour
Describe the affect of downwards herniation of the brain on brainstem functions
- Coma
- Altered respiratory rate
- Altered HR
- Altered BP control
- Death from cardiorespiratory arrest
Explain the effect a head injury will have on CPP
- ICP increases after injury, decreasing the CPP
- Blood flows from high to low pressure, raised ICP decreases the pressure gradient favouring blood flow to the brain
- Normally the brain autoregulates bloodflow regardless of pressure by changing the resistance of vessels, but after injury these homeostatic mechanisms fail
- Increasing ICP leads to decreasing CPP and ischaemic damage
Describe the stages of brain herniation
- Displacement of cingulate gyrus from one hemisphere to another under the falx cerebri
- Brain moves downwards (uncle herniation)
- Brainstem affected
List the types of primary injury and give examples
- Focal - localised to site of impact
- Fracture
- Haematoma - localised bleeding outside blood vessels
- Polar
- Cerebral contusions - multiple microhaemorrhages, small blood vessels leak into brain tissue
- Usually occur coup (adjacent to site of impact) or contre coup (diagonally opposite)
- Diffuse - movements of the brain within the cranial cavity causing widespread neurol damage
- Diffuse axonal injury - ‘stretching’ injury to the neurons + axons throughout the brain
Describe the Glasgow Coma Scale
- Eye opening
- Spontaneous - 4
- To sound - 3
- To pressure - 2
- None - 1
- Verbal response
- Oriented - 5
- Confused - 4
- Words - 3
- Sounds - 2
- None - 1
- Motor response
- Obey commands - 6
- Localising to pain - 5
- Normal flexion - 4
- Abnormal flexion - 3
- Extension - 2
- None - 1
Define the Glasgow Coma Scale
A standardised test developed for assessing the level of consciousness in acutely brain injured individual
How is CPP used clinically?
As a surrogate marker for cerebral blood flow
Describe an intracerebral haematoma
Blood within substance of brain
List the types of intracranial haematomas
- Extradural/epidural
- Subdural
- Intracranial
- Subarachnoid
How is ICP measured clinically?
- Can be measured directly - invasive so not usually done
- Neurological observations used to detect increasing ICP after head injuries
- GCS
- Vitals - pulse, BP, temperature
- Pupil responses
- Motor/sensory response
- Every 15 minutes
List the signs of increasing ICP
- Decreasing GCS
- Lack of pupillary response to light
- Lateralising signs - weakness on L or R
How is cerebral perfusion pressure related to intracranial pressure?
CPP = MAP (mean arterial pressure) - ICP
As ICP rises, CPP falls
Describe the development of an extradural haematoma
- Usually arterial bleeding, often from the middle meningeal artery
- Blood collects between the periosteal layer of the dura and the skull
- Periosteal dura is fixed to skull at sutures so blood can’t spread around the whole skull
Describe the procedure used to carry out the Glasgow coma scale
- Check - identify factors which may interfere with assessment e.g. hearing impairment
- Observe for spontaneous behaviour
- Stimulate if no spontaneous response
- Rate
Describe subarachnoid haematomas
Blood collects under arachnoid layer
Describe uncle herniation and clinical signs
- Herniation of the medial temporal lobe from middle to posterior cranial fossa across the tentorial opening
- Uncus is compressed against midbrain - compresses oculomotor nerve
- Parasympathetic fibres travel on outside of oculomotor nerve - fixed and dilated pupil seen before deviation of eye in down and out position
Describe the compensatory mechanism of the brain in response to an expanding mass lesion
- Compensatory capacity is limited
- CSF - 75ml displaced into spinal theca/venous system via arachnoid granules
- Intracranial venous blood - 75ml redistributed peripherally
- Brain is incompressible
- Arterial volume must remain constant - need to maintain blood supply to brain
- Initially as mass expands, CSF and venous blood redistribution maintains ICP
- Reaches critical point - limit of compensation reached (mass lesion >100-120ml)
- ICP rises exponentially
Describe the Monroe-Kellie Principle
- Within the skull, there is brain (80%), CSF and blood (venous and arterial)
- ICP must be kept constant - the skull is a rigid container which can’t expand
- If the volume inside the skull increases, this must be offset by an equal decrease in the volume of the other components to keep the ICP constant
List the common types of facial fracture
- Zygomaticomaxillary complex (tripod) fracture
- LeFort I, II or III
- Zygomatic fracture
- Orbital floor (‘blow-out’)
Define a zygomaticomaxillary (tripod) fracture
- Most common
- Involves separation of all three major attachments of the zygomatic bone to the rest of the face
- Can cause impingement of temporalis muscle - inability to open mouth
Define an orbital floor fracture
- Usual mechanism is a blow to the eye
- Thin floor of orbit fractures, eye drops into maxillary sinus
Describe LeFort fractures
- LeFort I
- Horizontal, floating palate, transmaxillary
- Floating fragment - lower maxilla and maxillary teeth
- LeFort II
- Pyramidal
- Commonly due to downwards blow to nasal area
- Fracture through the inferior orbital floor
- LeFort III
- Transverse, craniofacial dissociation
- Most severe - detachement of facial skeleton from cranium
- Fracture through zygomatic arch
