Pathology of Head Injury

Question 1

What is the Epidemiology of Head Injury?

Answer 1

• Head injury is the commonest cause of death and disability in people aged 1–40 years in the UK
• Commonest causes = RTAs, and alcohol-related incidents (including assaults)

Question 2

What is the Aetiology of Head Injury?

Answer 2

• Primary insult:
• > Focal and/or diffuse brain trauma
• Secondary insult:
• > Hypotension - low arterial BP
• > Hypoxia - low blood O2
• > Infection
• > Haematoma - bleeding in/around brain

Question 3

What is the Classification of Head Injury?

Answer 3

• Glasgow Coma Scale
• Correlates with severity of head injury
• 13-15 = mild injury
• 9-12 = moderate injury
• 3-8 = severe injury

Question 4

What are the complications of Head Injury?

Answer 4

• Permanent physical disability
• Post-traumatic epilepsy
• IC infection
• Psychiatric illness
• “Punch-drunk” Dementia
• Fatal outcome (uncommon)

Question 5

What are the different types of Skull fracture?

Answer 5

1 - Linear

• > commonly temporo-parietal
• > from blow or fall onto side

2 - Depressed

• > focal impact which may push fragments inwards to damage the meninges, BVs and brain
• > risk of meningitis and post-traumatic epilepsy

3 - Comminuted (mosaic)
-> fragmented skull

4 - “Ring” Fracture

• > ie. fall from a height and landing on the feet
• > fracture line encircling the Foramen Magnum
• > skull base + cervical spine forced together

5 - “Contre-Coup” Fracture
-> fracture to the orbital plates (front of the skull), caused by a fall onto the back of the skull

Question 6

What are the key features of an Extradural Haematoma?

Answer 6

• bleeding between the dura and the skull
• vast majority due to skull fracture (squamous temporal bone)
• classically caused by bleeding from the Middle Meningeal Artery
• accumulation of blood can causes raised ICP -> developing neurological symptoms
• “Lucid interval” can occur
• Lentiform shape on CT (due to sutures)

Question 7

What are the key features of a Subdural Haematoma?

Answer 7

• bleeding occurring between the Dura and Arachnoid
• more common than EDH
• bleeding from bridging veins (drains into the large venous channels within the dura)
• usually due to Trauma ie. accelerated fall
• > due to tearing of small bridging veins on brain surface
• > pts with atrophic (small) brains at greater risk due to the greater capacity for movement (and “shearing” of the veins)
• occurs WITHOUT a skull fracture
• “Lucid interval” can be seen
• Crescent shape on CT
• chronic SDH can be a cause of chronic confusion in the elderly -> may get mistaken for Dementia

Question 8

What are the key features of SAH?

Answer 8

• Bleeding beneath the arachnoid mater (and above the brain)
• Most common cause of SAH is natural disease - rupture of a cerebral artery “berry” aneurysm
• frequently seen in association with cerebral contusions (bruising to the brain)
• Traumatic Basal SAH = due to rupture of the vertebro-basilar circulation
• > (caused by forceful impact to the upper part of the side of the neck, causing abrupt rotational movement of the head)
• > Collapse is usually rapid and death can occur v quickly (due to build up of irritants from the blood in the subarachnoid space)

Question 9

What are the different outcomes of intrinsic traumatic brain injury?

Answer 9

• Cerebral Oedema
• Cerebral contusion + laceration
• > Coup contusion
• > Contre-coup contusion
• Diffuse Axonal Injury

Question 10

What is the cause of death in Cerebral Oedema?

Answer 10

• Raised ICP due to brain swelling
• > brain swelling in response to focal/diffuse injury
• > also due to secondary brain ischaemia

Question 11

What is the difference between a “coup” and a “contre-coup” contusion?

Answer 11

• Coup contusion = occurs when head is hit by a heavy blow -> the contusion is found directly under the site of impact
• Contre-coup contusion = caused by a moving head striking a fixed object or an unyielding surface -> ie. fall to back of head causes contusions in the back and the front of the head

Question 12

What are the key features of Diffuse Axonal Injury?

Answer 12

• not just caused by trauma -> use the term tDAI
• diagnosis made by microscopy of brain tissue: diffuse damage to small BVs
• associated with vehicular collisions and falls from a height
• victims usually comatose when tDAI fully develops
• concussion = a clinical manifestation of lesser degrees of axonal injury (may have retrograde amnesia)