29. Head injury

Question 1

What tries to act as protection for the brain during trauma?

What is the main problem with this?

Answer 1

Brain is enclosed in the rigid skull - the skull acts to provide some protection

BUT skull is rigid - if the brain swells or a haematoma takes up the extra space - the brain becomes compressed

Question 2

What is the Munro-Kellie doctorine?

Answer 2

This acts to explain the relationship between intracranial content and intracranial pressure
This states that the intracranial volume is fixed and the intracranial volume and it’s contents creates a state of equilibrium
Any increase in the volume of one of the cranial components must be compensates by a decrease in the volume of another
These components include the brain tissue, CSF and the blood

Question 3

What is a space occupying lesion/mass lesion?

What occurs as a result of this?

Answer 3

This is when there is the presence of something extra in the cranial cavity e.g. blood clot/swelling of the brain/brain tumour e.g. a haematoma

These may be compensated for by a displacement of the CSF into the spine through the foramen magnum or by a draining of venous blood into the circulation

Question 4

What is the point of decompensation?

Answer 4

This is if there can no longer be any further compensation to cope with the decreased available space and the ICP starts to increase

Question 5

What is the cerebral perfusion pressure (CPP)?

Answer 5

This is the difference between the mean arterial pressure (MAP) and the ICP
CPP = MAP - ICP
This is the pressure responsible for the perfusion of the brain

Question 6

What is the mean arterial pressure?

Answer 6

This is the pressure at which most other organs are perfused with blood

Question 7

What is the effect on the brain of an increasing ICP?

Answer 7

As the ICP increased, the CPP decreases and this means that the brain will not be perfused as it should be - the cerebral blood flow (CBF) will decrease - requires a high O2 demand
An increasing ICP also results in a herniation of the brain out of the skull

Question 8

At which points of the skull can a brain herniation occur?

Answer 8

Subfalcine - the frontal lobe is pushed under the falx cerebri - results in leg weakness
Falx - Motor cortex can be pushed under the falx
Uncul hernation - the uncus can be squeezed through the tentorial hiatus (this usually transmits the midbrain and so the midbrain becomes compressed)
Tonsillar hernation - The tonsillar cerebellum can herniate through the foramen magnum past the brainstem - if severe enough, this can result in the patient being brain dead

Question 9

What is the impact of an uncul herniation and how does this present?

Answer 9

This will result in damage to the occulomotor nerve (CNIII)

The pupil dilates and becomes fixed - this occurs on the same side as the herniation

Question 10

What is the unucs?

Answer 10

This is the medial part of the temporal lobe

Question 11

What other damage occurs during a herniation of the brain?

Answer 11

Can result in damage to the blood vessels going to the brain stem
Duret haemorrhage - when this occurs to the blood vessels to the pons and then the pons ceases to function

Question 12

What are the layers of the meninges?

Answer 12

Dura mater
Arachnoid
Pia mater

Question 13

What are the two parts of the dura mater?

Answer 13

Periosteal layer

Meningeal layer

Question 14

What is the significance of the periosteum of the dura?

Answer 14

Fibrous layer that surrounds the brain and holds the blood vessels

Question 15

Which region of the meninges can be easily split from the rest?

Answer 15

The arachnoid layer can easily come apart - potential space

Results in the veins of this layer to tear and this can result in the development of haematomas

Question 16

What is a subarachnoid haemorrhage?

Answer 16

Where there is a bleed into the real space beneath the arachnoid layer where CSF ordinarily circulates

Question 17

What is the extradural space and when might this become a real space?

Answer 17

This is the potential space between the two layers of the dura
When fractures run through the skull where trauma is applied to the meningeal artery but can also occur at any point where there is a fracture
These may not present immediately after trauma but can develop slowly

Question 18

What is the impact of haemorrhages on the brain?

Answer 18

These will result in a decreased space and so an increased ICP
This will then result in a decreased CPP and then a decrease in CBF

Question 19

What is muco-pus and what is the significance of this when there is a head injury?

Answer 19

Muco-pus is snot - contains bacteria
Sinuses at the base of the skull are full of this so the snot/muco-pus is just mms away from the brain
During trauma, if the base of the skull is damaged and torn, this can result in bacteria from the muco-pus reaching the brain and entering the spaces between the meninges
This can result in meningitis, encephalitis and abbess formation at the brain

Question 20

When there is trauma to the head, where else should you check for trauma?

Answer 20

At the cervical spine - a significant blow to the head may damage this region

Question 21

Briefly describe the molecular pathology of trauma to the brain

How can this be treated?

Answer 21

Immediately following the trauma, the neurones and brain axons will appear to be normal
After a few days, there will be active and programmed cell death i.e. apoptosis
The neurones will die and swell - be lost via cytotoxic oedema

Aiming to provide neuroprotection - therapy aimed at preventing neuronal cell death after injury
Implement some form of brain repair - a mechanism which allows for the generation of new neurones and the growth of new axons

Question 22

What is the relevance of a coma to head injury?

Answer 22

Patients who suffer a severe head injury will enter a coma - they will have a low conscious level

Question 23

What are the issues with ICP in comatose patients?

Answer 23

Patients in a coma do not protect their airways very well - do not swallow or cough etc and so substances can accumulate in their pharynx and can obstruct their airways
As the conscious level falls, the ventilation rate also falls - will result in an increased CO2 level in the brain - this results in a dilation of the blood vessels and an increase in ICP
These patients also have a slightly lower blood pressure - this means that their MAP is decreased and will impact the CCP

Question 24

What are the principles of management in patients with a head injury?

Answer 24

Must counteract the effects of both primary brain injuries and secondary brain injuries

Early CT scan to identify haematoma quickly
Rapid referral to neurosurgery - better outcome within 4 hours for craniotomy
Increase the ventilation rate of the patient to higher than normal - allows CO2 levels to decrease and blood vessels to constrict - decreased ICP
Seduce the patient to reduce the O2 requirement of the brain