Traumatic Brain Injury

Question 1

What is TBI?

Answer 1

A non-degenerative, non-congenital insult to the brain from an external mechanical force to the head, face or spine possibly leading to permanent or temporary impairment of cognitive, physical and psychosocial functions with an associated diminished or altered state of consciousness

Question 2

Whom does TBI primarily affect?

Answer 2

Males ~80%

Under age of 45

Question 3

In what ways can TBI be classified?

Answer 3

Severity - GCS, duration of LOC, length of post traumatic amnesia
Location and appearance - focal injury or diffuse injury

Question 4

What is the significance of post traumatic amnesia in TBI?

Answer 4

The longer you are aren’t able to form memories after TBI the more likely you are to have cognitive dysfunction

Question 5

Focal injuries vs diffuse injuries

Answer 5

Focal injuries - contusions, intracranial haemorrhage

Diffuse injuries - most injuries, not visible on a CT scan

Question 6

What proxy is used to define some neurological injuries?

Answer 6

Blood - often refer to where the haemorrhage is e.g. subdural

Question 7

What is the primary injury in TBI?

Answer 7

A mechanical event and occurs at the time of injury. Considered to be irreversible i.e. straining/tearing of axons and tearing of vessels

Question 8

What is the secondary injury in TBI?

Answer 8

Several delayed pathological process which occur as a result of the primary injury e.g. ICP, Ischaemia, Oxygen free radicals

Question 9

How would a diffuse absurd injury appear on a CT scan?

Answer 9

Not many abnormalities, some small dots indicating small haemorrhages. The damage is at an axonal level and so not visible on scans.

Question 10

What level of consciousness would a patient with a diffuse absurd injury have?

Answer 10

In coma, patients present with LOC from outset

May be in the coma for a long period of time and may never emerge from it

Question 11

What is associated with diffuse absurd injuries?

Answer 11

Vegetative state, disability and poor outcomes

Question 12

What causes diffuse absurd injuries and how does velocity affect the injury?

Answer 12

Caused by acceleration/deceleration and rotational forces (common in RTC).
The stronger the forces applied the deeper the impact of damage - high velocity injuries cause damage to the midbrain and thalamus

Question 13

What is an extradural haemorrhage and what are its characteristics?

Answer 13

Blood accumulates between the skull and dura mater.
Lens like appearance of a scan
Patients often have a lucid interval

Question 14

What is a lucid interval in terms of TBI?

Answer 14

Initial brief LOC which pt recovers from. Pt then develops a headache and eventually seizes

Question 15

What is a subdural haemorrhage and what are its characteristics?

Answer 15

Bleeding between dura mater and arachnoid mater
Biconcave shape on scan
Associated with high velocity injuries
Signs: reduced GCS, drowsiness, headache, pupillary changes

Question 16

Why are SDH common in the elderly?

Answer 16

Brain shrinks with age so there is more natural space between the brain and dura mater

Question 17

What is an intracerebral haematoma and what are its characteristics?

Answer 17

Bleeding within the brain itself usually within the white matter of frontal and temporal lobes
Related to poor outcomes and high morbidity
Dilated pupil on side of the lesion and hemiplegia on the opposite side to the lesion

Question 18

What are contusions and what are their characteristics?

Answer 18

Bruising in the brain
Not necessarily associated with severe injury - relatively common
Common in those on blood thinning medication - particularly warfrin and anti platelet medication
Often found in frontal and temporal lobes

Question 19

What are coup and contracoup injuries?

Answer 19

Coup - Found at site of impact

Contracoup - Found at opposite side to impact, caused by deceleration

Question 20

What is a subarachnoid haemorrhage and what are its characteristics?

Answer 20

Bleeding below the arachnoid layer

High risk of developing hydrocephalus due to blocked arachnoid villi

Question 21

What occurs at a cellular level during a simple disturbance such as concussion?

Answer 21

Axonal injury -> electrochemical discharge due to Ca2+ influx or some proteins sensing stretch of the axon -> release of NT into the synapse

Question 22

Other than axonal stretch what other cellular effects are seen during TBI?

Answer 22

Damage to microtubules in axon cytoskeleton - impaired axonal transmission as compounds can be transported along the axon
Migration of inflammatory cells around the nerve sheeth - response from microglia and external inflammatory cells, attracted by leak of DAMPs and cytokines from damaged cells

Question 23

What is the significance of raised ICP?

Answer 23

Blood flow is impeded by raised ICP, when brain pressure > capillary pressure, perfusion stops
Sustained and uncontrolled rises in ICP are normally fatal

Question 24

Mechanisms leading to raised ICP:

Answer 24

Cytotoxic oedema - ischaemia, direct neural disruption
Vasogenic oedema - blood brain barrier injury
CSF volume
Haemamtoma
Raised cerebral blood volume

Question 25

How does an ischaemic injury occur in TBI?

Answer 25

Brain has a high metabolic demand as it is unable to store energy and required a constant supply of O2 and glucose to generate ATP. If hypoperfusion is maintained then there will be death of some brain cells

Question 26

How would a graph of ICP against volume look like and why?

Answer 26

Initially flat/slow rise but then becomes exponential Initially there is not a rise in ICP as volume increases but as compensatory mechanisms are exhausted there is a sharp rise in ICP

Question 27

Why is the shape of the ICP Volume curve useful?

Answer 27

The curve works in reverse meaning even small interventions such as analgesia or straightening the neck can have a large effect on reducing ICP

Question 28

Why is ICP still lowered despite no studies showing it improves outcomes?

Answer 28

One of the few things that can be controlled and treated | There are some scenarios where ICP can't be allowed to rise as it would be certainly fatal

Question 29

Measures to control ICP:

Answer 29

``` Control fever Control seizures Manipulate blood pressure Manage electrolyte levels Levels of sedation and analgesia ```

Question 30

Why does coma occur?

Answer 30

Due to functional damage not a protective response

Question 31

What occurs when the brain is damage by an impact?

Answer 31

Area of the brain directly damaged by impact - area is not dead but is profoundly affected and prone to swelling As the area swells it pushes on adjacent areas which then become ischaemic and damage propagates to further areas.

Question 32

How does stretching the axon result in Injury?

Answer 32

The axon stretched causing the opening of mechanical Ca2+ channels leading to an influx of Ca2 and depolarisation. This opens voltage gated Ca2+ channels and causes further Ca2+ influx and depolarisation. Mitochondria become overloaded with Ca2+ leading to the mitochondria stop working and the production of oxygen free radicals. Ca2+ influx also activates lipase and proteases via secondary messengers causing cell digestion. Stretching the axon also damages microtubules, reducing axon transport which causes glutamate release which further increases Ca2+ influx

Question 33

How does the brain control its own blood supply and why can this be used in TBI treatment?

Answer 33

There is normally a zone of autoregulation where an increase in BP leads to vasoconstriction and so reduces blood volume entering the brain which in turn will reduce ICP - however sometimes this mechanism is compromised in TBI and an increase in BP leads to an increase in ICP

Question 34

Why does sedation cause ICP to fall?

Answer 34

It relaxes muscles so venous return from the brain isn't affected which reduces blood volume in the brain and so lowers ICP

Question 35

What are second line therapies for increasing ICP?

Answer 35

Manipulate BP Therapeutic hypothermia Decompressive surgery Deep coma

Question 36

What is the trade off with decompressive surgery?

Answer 36

Increases the rate of survival but at the expense of increased disability

Question 37

What is the effect of TXA on TBI?

Answer 37

Shows a significant reduction in mortality for mild to moderate injury but there are less clear effects for those with severe injuries

Question 38

What is concussion?

Answer 38

A transient impairment of neurological function after mechanical injury

Question 39

Why are mTBI likely to be under reported?

Answer 39

Most patients have a spontaneous resolution of symptoms even in the absence of medical care

Question 40

Repeated concussion is associated with

Answer 40

Depression, Chronic neurodegenerative conditions later in life - Parkinson's disease, motor neuron disease

Question 41

Why don't mTBI show up on scans?

Answer 41

Don't typically cause structural injury to the brain