Head Injury Flashcards
What is a diffuse axonal injury (DAI)?
The shearing of the brain’s long connecting nerve fibers (axons) that happens when the brain is injured as it shifts and rotates inside the bony skull.
This is considered one of the most common and detrimental forms of traumatic brain injury (TBI).
What is a brain contusion?
A bruise to the brain: causes bleeding and swelling inside of the brain around the area where the head was struck.
When does 2ary brain injury occur?
This occurs when cerebral oedema, ischaemia, infection, tonsillar or tentorial herniation exacerbates the original injury.
The normal cerebral auto regulatory processes are disrupted following trauma rendering the brain more susceptible to blood flow changes and hypoxia.
What happens in DAI?
The resistant inertia that occurs to the brain at the time of injury, preceding and following its sudden acceleration against the solid skull, causes shearing of the axonal tracts of the white matter.
Axonal disconnection and mechanical disruption to axonal cytoskeletal structure results in immediate severe brain injury.
What is the most frequent cause of DAI?
Road traffic accidents (RTAs)
Causes of DAI?
1) RTAs
2) Assault
3) Falls
4) Child abuse e.g. shaken baby syndrome and abusive head trauma.
DAIs can be classified into what 3 categories?
Grade I
Grade II
Grade III
What occurs in Grade I DAI?
What is the effect on consciousness?
What –> Diffuse axonal damage within the white matter of the cerebral hemispheres and grey-white matter interfaces.
Effect –> Brief loss of consciousness
What occurs in Grade II DAI?
What is the effect on consciousness?
What –> Tissue tear haemorrhages present; axonal damage of the white matter including grade 1 regions and the territory of the corpus callosum.
Effect –> Variable recovery process, coma of unclear duration.
What occurs in Grade III DAI?
What is the effect on consciousness?
What –> Grade 2 findings in addition to tissue tear haemorrhages within the brainstem
Effect –> Instant coma with posturing and incomplete recovery
What are the 2 pathognomonic histological findings of axons with DAI?
1) Axonal varicosities – periodic swelling along the axonal length at the site of injury, secondary to the interrupted axonal transport
2) Axonal bulb – Single large swellings at the site of disconnection, following complete axonal severance
Clinical features of DAI?
1) LOC at time of injury
2) Prolonged post-traumatic coma (often attributed to co-existent injury, e.g. acute haemorrhage or cerebral contusions)
3) The diagnosis is often only suspected when patients do not make a neurological recovery
What is the main differential for DAI?
The main differential in cases of head injury are cortical contusions, typically found superficially at the cortical level, not concentrated to the grey-white matter junction.
1st line imaging following head injury?
CT within contrast
1st line imaging for DAI detection?
MRI
Management of DAI?
Following any trauma, patients should be appropriately resuscitated and stabilised, prior to transfer to a neuro-trauma centre.
Therapeutic interventions for DAI are limited. Options are all aimed to preventing secondary effects such as cerebral oedema or haemorrhage.
Prognosis of DAI?
A spectrum of clinical consequences may follow DAI, dependent on the severity of the pathology ranging from very minor to extensively diffuse damage.
Long-term vegetative state appears at the severe end of the spectrum. There is a predictive correlation between the extent of brainstem DAI and likelihood of persistent vegetative state.
What is the Cushing’s reflex?
A triad of signs that are indicative of raised ICP.
1) Bradycardia
2) Irregular respirations
3) Widened pulse pressure (increasing systolic, decreasing diastolic)
What does the Cushing’s reflex indicate?
often occurs late and is usually a pre terminal event
What are the 4 types of intracranial haemorrhage?
1) Extradural (epidural) haemorrhage
2) Subdural haemorrhage
3) Subarachnoid haemorrhage (SAH)
4) Intracerebral haemorrhage
What is an extradural (epidural) haemorrhage?
Bleeding into the space between the dura mater and the skull.
Risk factors for an intracranial haemorrhage?
- Head injuries
- Hypertension
- Aneurysms
- Ischaemic strokes (progressing to bleeding)
- Brain tumours
- Thrombocytopenia (low platelets)
- Bleeding disorders (e.g., haemophilia)
- Anticoagulants (e.g., DOACs or warfarin)
An extradural haemorrhage is usually caused by rupture of what artery?
The middle meningeal artery in the temporoparietal region.
This is vulnerable to injury as the thin skull at the pterion overlies the middle meningeal artery.
What is an extradural haemorrhage often caused by?
It is almost always caused by trauma and most typically by ‘low-impact’ trauma (e.g. a blow to the head or a fall).
A typical history is a young patient with a traumatic head injury and an ongoing headache.
How do patient with an extradural haemorrhage typically present?
1) Patient has period of improved neurological symptoms and consciousness
2) Followed by a rapid decline over hours as the haematoma gets large enough to compress the intracranial contents
3) Develops fixed and dilated pupil due to the compression of the parasympathetic fibers of the 3rd cranial nerve.
How does an extradural haemorrhage appear on a CT?
- Biconvex, hyperdense collection
- Limited by the cranial sutures (they do not cross the sutures, which are the points where the skull bones join together).
Where does a subdural haemorrhage occur?
Between the dura and the arachnoid mater.
Subdural haemorrhage is the result of the rupture of which vessel?
Caused by a rupture of the bridging veins in the outermost meningeal layer.
Who are subdural haemorrhages more common in?
Elderly & alcoholic patients –> have more atrophy in their brains, making the vessels more prone to rupture.
What is an ACUTE subdural haemorrhage usually the result of?
High-impact trauma
What is a CHRONIC subdural haemorrhage?
A collection of blood within the subdural space that has been present for weeks to months.
Presentation of a chronic subdural haemorrhage?
Typically a several week to month progressive history of either confusion, reduced consciousness or neurological deficit.
What will a subdural haemorrhage look like on a CT?
They have a crescent shape and are not limited by the cranial sutures (they can cross over the sutures).
How can a subdural haemorrhage be classified?
Acute: <3 days
Subacute: 3-21 days
Chronic: >21 days
What time period defines an acute subdural haemorrhage?
<3 days
What are the most common causes of a subdural haemorrhage?
1) Trauma (typically a blow to the temporal side of the head, rupturing the bridging cranial veins)
2) Rupture of a cerebral aneurysm
3) Rupture of an arteriovenous malformation (AVM)
4) Cerebral hypotension
5) Malignancy (rare)
Typical symptoms of a SDH?
Headache
Nausea/vomiting
Confusion
Drowsiness
Poor balance
Weakness
Paraesthesia or numbness
Presentation of an acute vs chronic SDH on CT?
Acute: typically has a hyperdense appearance (bright white)
Chronic: typically has a hypodense appearance (black/dark grey)
What does the hyperdense appearance on a head CT indicate?
The hyperdense appearance represents recently coagulated blood.
What does the hypodense appearance on a head CT indicate in SDH?
The hypodense appearance of chronic SDH represents the dissolution of cellular elements into liquified blood.
Risk factors for a SDH?
1) old age
2) alcoholism
3) anticoagulants
Describe onset of symptoms between epidural and subdural haemorrhage
There is a slower onset of symptoms in SDH compared to an epidural haematoma. There may be fluctuating confusion/consciousness.
What is a SAH?
Subarachnoid haemorrhage involves bleeding in the subarachnoid space, where the cerebrospinal fluid is located, between the pia mater and the arachnoid membrane.
What is the most common cause of SAH?
This is usually the result of a ruptured cerebral (berry) aneurysm.
What are the 2 types of SAH?
Traumatic & spontaneous
