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ANAT2012 > Brain > Flashcards

Brain Flashcards

1
Q

Name the 3 meningeal layers suspending the brain

A

dura (periosteal & meningeal), arachnoid & pia

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2
Q

Between which two meningeal layers does the majority of cerebrospinal fluid exist?

A

arachnoid mater & pia mater (called the subarachnoid space)

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3
Q

Where does the tentorium cerebelli lie within the brain?

A

between the cerebellum and the posterior cerebral hemispheres

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4
Q

Where are the supratentorial & infratentorial compartments in the brain?

A

above and below the level of the tentorium cerebelli

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5
Q

There is a greater principal strain in the corpus callous for a coronal rotational versus sagittal rotational force, what does this mean?

A

Injuries which cause rotational force in the coronal direction may be more severe than those which cause rotational force in the sagittal direction

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6
Q

During an impact to the head, how does the skull and brain outcomes vary depending on the direction of force?

A

During a straight on impact to the head, the skull is able to absorb a lot of the strain, whereas during an oblique impact (shearing) the skull does not absorb as much and more strain is passed on to the brain, often resulting in more severe injury

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7
Q

True or false… an impact to a head that is free to move is likely to result in greater injury that an impact to a head that is constrained

A

True

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8
Q

The brain is a poroelastic, fluid-saturated solid. What does this mean?

A

It is a solid material containing and surrounded by fluid

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9
Q

Does the brain have a high or low permeability?

A

Low

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10
Q

Does the brain have a high or a low bulk modulus?

A

High

Bulk modulus is how much you can decrease the volume of a material by compressing it on all sides. The brain has a high bulk modulus because its volume cannot be decreased very much due to how much fluid is present

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11
Q

The brain has a low compressive modulus and an even lower shear modulus, what does this mean for its sensitivity to loading?

A

The brain is more sensitive to shear loading than compressive loading

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12
Q

True or false… in general white matter is stiffer than grey matter in compression

When is this not the case?

A

True

White matter varies directionally (anisotropic) more than grey matter (isotropic) so this may vary depending on location

I.e. the corpus callosum fibres are arranged left to right and so the way that it behaves under strain will depend on which direction you are testing (left to right or ant. to post.)

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13
Q

Why are humans more likely to experience injuries to the brain than quadrupeds?

A

Brain mass: smaller brains tolerate much greater acceleration/deceleration forces (larger brains are heavier and gain more momentum than a lighter brain)

Alignment: in quadrupeds the long axis of the brain is parallel to the spinal cord whereas in humans they are at a right angle which may increase rotational shearing forces

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14
Q

How many brain injuries can be attributed to motor vehicle accidents?

A

More than ⅔

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15
Q

What is the difference between a traumatic brain injury and an acquired brain injury?

A

An acquired brain injury is any brain injury acquired after birth (I.e. stroke, poisoning etc)

Traumatic brain injury refers to a traumatically induced structural injury &/or physiologic disruption of brain function as a result of an external force (and falls under the heading of an acquired brain injury)

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16
Q

What are the clinical signs of a traumatic brain injury?

A

Any period or loss, or a decreased level, of consciousness

Any loss of memory (of events before or after the injury)

Any alteration in mental state at the time of injury (I.e. confusion, slowed thinking)

Neurological deficits (I.e. weakness, balance, visual, speech, general sensory)

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17
Q

What is diffuse axonal injury (DAI)?

A

A widespread disruption of white matter usually due to shearing forces

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18
Q

When does a extradural (aka epidural) haematoma occur?

A

Often following a skull fracture, some broken bone may pierce the middle meningeal artery resulting in bleeding into the extradural/epidural potential space

This potential space is between the skull and the endosteal (outer) layer of dura mater

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19
Q

When does a subdural haematoma occur?

A

Often following violent shaking of the head, the bridging veins connecting to the dural sinuses can be severed resulting in bleeding into the subdural potential space (aka shaken baby syndrome)

This potential space is between the meningeal layer of dura and the arachnoid

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20
Q

When does a subarachnoid haematoma occur?

A

Either due to stroke or aneurysm or an acceleration rotational trauma, there is bleeding from the cerebral arteries and veins resulting in blood joining the CSF in the subarachnoid space

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21
Q

Where does an intracerebral (parenchymal) haemorrhage occur?

A

Within the brain tissues due to a disruption in the veins/capillaries within the brain often following an acceleration/deceleration injury

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22
Q

Why is brain contusion often associated with subarachnoid haemorrhage?

A

Often if a brain contusion has occurred it can be assumed that the impact has also damaged the vascular structures between the skull and the brain in that location, resulting in subarachnoid haemorrhage

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23
Q

What is brain contusion?

A

Focal surface bruising on the brain resulting in cell death, bleeding & oedema

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24
Q

What is coup and contreceoup in regards to brain contusion?

A

Coup refers to contusion directly under the site of impact due to compressive forces whereas contreceoup refers to contusion on the opposite side of the brain due to inertia forcing the brain into the other side of the skull

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25
Q

Where does the falx cerebri lie within the brain and what areas of the brain does it seperate?

A

In the longitudinal fissure down the centre of the brain, it separates the right and left hemisphere partially to allow the corpus callosum passage

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26
Q

What does the tentorial notch encircle?

A

The midbrain allowing connection between the mid brain and the pons

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27
Q

What are the two major ridges between the anterior/middle cranial fossa & middle/posterior cranial fossa?

A

Spehnoidal crest

Petrous ridge

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28
Q

How would the weight of the brain vary if the cerebrospinal fluid was drained?

A

1500g with CFS, 50g without

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29
Q

What is the purpose of cerebrospinal fluid?

A

Cushions and protects the brain

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30
Q

The brain is very active metabolically & does not have an effective storage mechanism, what does this mean for blood supply?

A

The brain requires a continuous, relatively large (25%) blood supply in order to function

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31
Q

What is the purpose of the blood brain barrier? Why may this not always be a good thing?

A

A layer of epithelia cells provides a barrier where the blood stream cannot access the brain directly, this is to stop pathogens/harmful materials from entering the brain

Unfortunately this also means medicine cannot be used to go from the blood stream to the brain for possible lifesaving interventions (i.e Alzheimer’s)

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32
Q

What vascular structures contribute to interstitial fluid within the brain?

A

Leakage from capillaries across blood brain barrier
Ventricles across ependymal lining
Subarachnoid space across pial-glial lining

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33
Q

Why do we see more severe injuries from head impacts with an unconstrained head as opposed to a constrained head?

A

An impact to a constrained head has a large kinetic focal energy but a low cranial momentum

An impact to an unconstrained head has a relatively low kinetic energy but a large momentum, rotational, tensile and shear force which results in the brain bouncing around the skull more, hence more severe injury

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34
Q

The brain exhibits viscoelastic properties, what does this mean for strain rate? How does this vary in infants?

A

The adult brain will become stiffer under a faster strain rate, however this is not seen in infants as their brains have an equal compression and shear modulus which is insensitive to strain rate

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35
Q

What is the fibre alignment in the corona radiata?

A

Multi-axial (fanning outwards)

36
Q

What is the fibre alignment of the brain stem and internal capsule?

A

Vertically oriented (up/down)

37
Q

Which structure within the brain is most sensitive to shear stress?

A

The corpus callosum

This is because it is the most anisotropic and therefore has he lowest shear modulus

38
Q

What is the most common age bracket for brain injuries?

A

16-24 years

39
Q

How many of the yearly brain injuries are typically male?

A

~⅔

40
Q

How many Australians experience a stroke each year?

A

> 37,000

41
Q

How might a brain injury be classified?

A

By the physical mechanism

Symptoms/severity

Whether it’s a primary or secondary injury

Whether it’s focal, multi focal or diffuse

By the pathoanatomy

42
Q

What kinds of brain injuries may be seen following a linear impact?

A

Contusion, skull fracture, epidural haematoma

43
Q

What kind of brain injuries might be seen following an oblique impact?

A

Diffuse axonal injury, contusion, subdural haematoma, intracerebral haematoma

44
Q

What is primary traumatic brain injury? Give some examples

A

Irreversible damage that occurs at the time of injury

I.e. axonal injury, vascular injury (haemorrhage), contusion, laceration

45
Q

What makes axons vulnerable during a high velocity shearing force?

A

Their viscoelasticity (brittle response) and their high degree of alignment

46
Q

What is happening within the axons during diffuse axonal injury?

A

Damage occurs to the axonal cytoskeleton resulting in misalignment of the cytoskeleton

There is also mechanical damage to sodium channels > influx of sodium > axonal swelling > calcium influx > calcium activated proteolysis which damages the cytoskeleton further

This misalignment impairs axonal transport > accumulation of proteins in axonal swellings > secondary axotomy (severing of axons)

47
Q

What is a vascular brain injury?

A

Injury to vascular structures within the skull leading to bleeding into spaces and potential spaces

48
Q

What are potential spaces within the skull?

A

Where spaces may occur between connective tissue layers that should not normally occur due to bleeding into that space

I.e. between the skull and dura mater & between the dura mater and arachnoid mater

49
Q

When does a interventricular haemorrhage occur?

A

When the vascular structures lining the ventricles are broken and bleeding into the ventricles occurs

50
Q

Fractures of what part of the skull are more likely to result in an epidural haematoma and why?

A

Temporal fractures because this area of the skull overlies the middle meningeal artery

51
Q

How would an epidural haemorrhage present on a CT scan and why?

A

Biconvex shape due to the sutures (connecting bone to underlying dura) containing the bleed

52
Q

How would a subdural haematoma present on a CT and why?

A

Crescent shape as the bleed is being contained by the falx cerebri & tentorium cerebella

53
Q

Why might a slower developing subdural haematoma be more difficult to diagnose in an older patient?

A

The brain shrinks as we age and so it begins to be suspended by the bridging veins which makes them delicate and easily sheared hence a slower developing haematoma and a delayed diagnosis

54
Q

Is it possible to diagnose a subarachnoid haemorrhage with a spinal tap?

A

Yes- because there will be blood as well as CSF within the spinal cord

55
Q

What is the imaging of choice following an acute brain injury?

A

An unenhanced brain CT

They are widely available, fast and able to identify bleeds in the brain quite easily while also distinguishing between contusion & haemorrhage

56
Q

What is the downside to CT scans following a brain injury?

A

They are not able to detect subacute and chronic contusions, this is where an MRI is superior

57
Q

What is the Glasgow Coma Scale score and what three responses does it score?

A

A measurement of brain function often used during acute brain injuries to get an idea on the severity

The scale measures eye opening, verbal response & motor response

58
Q

How does the scoring work on the Glasgow Coma Scale score? What score indicates functional and what score indicates there is a severe injury to the brain?

A

You can score between 3-15, 3 being severe and 15 being almost normal

This score is taken from the lowest GCS score in the first 48 hours following injury

59
Q

On the Glasgow Coma Scale, what score would indicate a severe brain injury?

A

<9

60
Q

On the Glasgow Coma Scale, what score would indicate a moderate brain injury?

A

9-12

61
Q

On the Glasgow Coma Scale, what score would indicate a mild brain injury?

A

13-15

62
Q

How is consciousness used to determine the likely outcome of a traumatic brain injury?

A

It is the time to return to consciousness, there is a lower mortality rate if the patient returns to consciousness within 6 hours

63
Q

What is the most common severity level of traumatic brain injuries?

A

Mild (GCS 13-15)

64
Q

Someone who experiences a mild traumatic brain injury is likely to experience loss of consciousness for how long?

A

<30 minutes

65
Q

How long might someone with a mild traumatic brain injury experience amnesia?

A

<24 hours following the injury

66
Q

Is macroscopic injury usually seen with a mild traumatic,attic brain injury?

A

No

67
Q

What clinical signs might someone have with a mild traumatic brain injury?

A

Physical symptoms: fatigue, nausea, altered equilibrium, vision, hearing
Cognitive symptoms: altered attention, memory, processing, reasoning
Mood & behaviour: insomnia, irritability, depression, anxiety

68
Q

Mild traumatic brain injuries often have persisting difficulties with what?

A

Concentration & memory

69
Q

Why is it important for patients with a mild traumatic brain injury to have a follow up scan?

A

It is likely that the injury could progress and result in further haemorrhage (subdural most likely)

70
Q

When might a mild traumatic brain injury be considered for surgical intervention?

A

If there is a displaced skull fracture, a subdural or epidural haematoma > or = 10mm or a base deficit > or = 4

71
Q

Secondary traumatic brain injuries include:

A 
Ischaemia > hypoxic damage
Brain swelling/oedema
Raised intracranial pressure
Neuroinflammation 
Infection (due to breakdown of BBB)
72
Q

What is cytotoxic oedema?

A

Cellular swelling due to tissue damage disrupting the cell membrane pumps resulting in an influx of water into the cell

This often results in apoptosis

73
Q

What is vasogenic oedema?

A

Tissue swelling due to tissue damage disrupting the BBB resulting in an increased BBB permeability and an influx of water into tissue from capillaries

74
Q

Normally the brain receives ~55ml of blood per minute. What happens if this is decreased to ~20ml? What about ~10ml?

A

At ~20ml/minute neurons cease generating electrical signals

At ~10ml/minute for a few minutes there is necrosis

75
Q

There are two main strokes, what are they?

A

Ischaemic stroke & haemorrhagic stroke

76
Q

How common are ischaemic strokes and what is the mechanism?

A

Most common type of stroke, classified by a sudden blockage of blood flow to the CNS

77
Q

What causes the blockage during an ischaemic stroke?

A

Thrombus (a blood clot)

Embolus (a piece of plaque travels from its original site and blocks an artery downstream)

78
Q

What are the two types of haemorrhagic stroke?

A

Intracerebral haemorrhage (bleeding directly into brain tissue)

Subarachnoid haemorrhage (bleeding into the subarachnoid space)

79
Q

What are some causes of haemorrhagic stroke?

A

Hypertension

Rupture of an aneurysm

Vascular malformation

Complication of anticoagulant medication

80
Q

How prevalent are intracerebral haemorrhage strokes?

A

~10-15% of all strokes

81
Q

Where in the brain is most susceptible to intracerebral haemorrhage strokes?

A

Basal ganglia & thalamus

82
Q

How prevalent are subarachnoid haemorrhage strokes?

A

~5% of all strokes

83
Q

How do we diagnose a subarachnoid haemorrhage?

A

Very very severe headache
Sudden onset
Neck pain/stiffness
Non-contrast CT +/- lumbar puncture

84
Q

Explain the incidence of different types of stroke

A

Ischaemic > intracranial haemorrhage > subarachnoid haemorrhage

85
Q

Explain the morbidity & mortality of different types of stroke

A

Subarachnoid haemorrhage > intracranial haemorrhage > ischaemic

86
Q

What are some risk factors for stroke?

A

Age
Gender
Family history
Previous incident

Smoking
Alcohol
High blood pressure

ANAT2012 (10 decks)

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