Neuroanatomy: ICP and herniation

Question 1

Outline the brain components that contribute to intracranial pressure.

Answer 1

CSF 10%
Intravascular blood 12%
Brain tissue 78%

Question 2

DIscuss the Monroe-Kellie Doctrine.

Answer 2

one component increases another must decrease to maintain ICP. 5-15mmHg

Question 3

List compensatory mechanisms in response to increased ICP.

Answer 3

• Changes in CSF volume
• Changes in intracranial blood volume
• Changes in tissue brain volume

Question 4

Discuss the complications of decompensated raised ICP.

Answer 4

Exponential increase in ICP
herniation and death

Question 5

Outline cerebral blood flow.

Answer 5

The amount of blood in milliliters passing through
100g of brain tissue in 1 minute
grey: 170ml/min
white: 50ml/min

Question 6

Discuss Cerebral Perfusion Pressure.

Answer 6

is the pressure needed to overcome the ICP in order to deliver O2 and nutrients
CPP=MAP-ICP
CPP of 85mmHg is normal

• CPP < 50 mmHg ➔cerebral ischaemia
• CPP < 30 mmHg ➔brain death

Question 7

Discuss the regulatory mechanism of cerebral blood flow flow.

Answer 7

Autoregulation
* Changing diameter of blood vessels
* Ensures consistent CBF
* Only effective if mean arterial pressure (MAP) is70-150 mm Hg

Metabolic regulation
PCO2
PO2
Acidosis

Question 8

Describe the pathophysiology of tissue injury and how it ends up in an increased cranial pressure.

Answer 8

insult to the brain leads to tissue edema
compression of ventricles and blood vessels, decrease cerebral flow, and decrease O2 delivery. Death of brain cells leads to edema and necrotic tissue. Increase in ICP and compression of the brainstem and resp center. Accumulation of CO2 causes vasodilation and further increases ICP, due increase in blood volume, death!

Question 9

Discuss subfalcine herniation.

Answer 9

• Ipsilateral cingulate gyrus pushed beneath anterior falx cerebri
• Results in infarction of distal territory of anterior cerebral artery

Question 10

Discuss Transtentorial (uncal) herniation.

Answer 10

• Ipsilateral medial temporal lobe is squeezed under and across tentorium cerebelli

compress CN3, cerebral aqueduct
infarction of temporal and occipital lobe
Kernohan’s: leads to compression of the contralateral cerebral peduncle against the free edge of the cerebellar tentorium

Question 11

Discuss central herniation.

Answer 11

Also called descending transtentorial herniation
The Diencephalon (thalamus and hypothalamus) and medial parts of the temporal lobe are forced through the tentorial notch.

PinPoint pupils (miosis)
Duret haemorrhages
* small linear areas of bleeding in the midbrain and upper pons of the brainstem

Question 12

Describe tonsilar herniation.

Answer 12

Infratentorial mass forces cerebellar tonsils through foramen magnum.

Compression of the brainstem leads to coma and death.

Compression of PICA and vertebral arteries causing
ischaemia of brainstem, tonsils and lower
cerebellum

Question 13

Discuss upward herniation.

Answer 13

Also called ascending transtentorial herniation
Infratentorial mass compresses the brainstem
Displacement of brainstem and cerebellum through the tentorial notch

Flattening of the quadrigeminal cistern
Occlusion of PCA and SCA leading to territorial infarct
Cerebellum pushes cerebral aqueduct closed causing hydrocepahlus.

Question 14

Discuss transcalvarial herniations.

Answer 14

Also known as external herniation
Displacement/mush rooming of brain through defect in skull e.g. fracture site or craniotemy