Pathophysiology and Management of Raised Intracranial Pressure

Question 1

What is the normal ICP?

Answer 1

7-20 cmH₂O

(5 - 15 mmHg)

Question 2

What is autoregulation in the brian?

Answer 2

the maintainance of adequate blood flow to the brain thorough vasoconstriction and vasodilation of small arterioes

Question 3

What is chemoregulation in the brain, and therefore what would be the effect of breath holding?

Answer 3

altering blood flow in response to pH/CO₂ levels

breath holding > elevates CO₂ (dropping pH) > vasodilation to increase blood flow

Question 4

If a patient were to develop an intracranial mass, how would the volume contribution of each of the components of the cranial cavity change?

Answer 4

reduce venous blood volume

reduce CSF volume

Question 5

How can decreased blood flow in the brain lead to cerebral oedema?

Answer 5

decreased blood flow > neuronal cell hypoxia > failure of Na⁺/K⁺ATPase > intracelular Na+ rises > water moves into cells > neuronal swelling > further compression of blood vessels and increase in ICP > decreased blood flow cycle continues

Question 6

Why do patients report an increase in headache due to raised ICP first thing in the morning?

Answer 6

intracranial venous pressure is increased when lying flat (normally around -10mmHg when standing)

hypoventilation during sleep > elevated CO₂ > cerebral arteriole vasodilation > increased blood flow > increaed pressure

Question 7

Why does coughing, bending and sneezing increase headaches due to raised ICP?

Answer 7

increase in thoracic pressure causes SVC inflow obstruction, limiting venous drainage from head

Question 8

What may be seen on fundoscopy if a rise in ICP has been very sudden?

Answer 8

Retinal Haemorrhages

Question 9

Why may a patient with raised ICP present with vision loss?

Answer 9

compression of the optic nerve
(surrounded by dura mater)

Question 10

What is belived to cause vomiting in patinet with raised ICP?

Answer 10

hypoxia stimulates the vomiting centre in the brainstem

Question 11

How may a slowly increasing ICP manifest in an infant?

Answer 11

increasing head circumference size

Question 12

Summary of raised ICP

Answer 12

Summary of raised ICP

Question 13

Why may a CN6 palsy present as a false lateralising lesion in a patinets with riased ICP?

Answer 13

CN6 origniates from posterior pons

runs ventrally over petrous part of temporal bone

raised ICP can compress CN6 against cranial floor

riased ICP may be due to a mass anywhere in cranial value but CN6 palsy would suggest it was around that region

Question 14

What is a subfalcine herniation and why may some patinets present with contralateral leg weakness, whereas others could be asymptomatic?

Answer 14

herniation of the cingulate gyrus under the falx cerebri

hernation can lead to compression of anterior cerebral artery > supplies medial aspect of pre-central gyrus (primary motor cortex) with humuncular correlation to the lower limb

Question 15

What are the possible effects of uncal herniation over the tentorium cereblli?

Answer 15

ipsilateral occulomotor nerve palsy
(dilated pupil due to loss of parasympathetics)

compression of cerebral peduncle
(contralateral leg weakness)

decreased level of consciousness
(compression of RAS in brainstem)

Question 16

What is the greatest threat to life following a tonsilar herniation?

Answer 16

compression of the respiratory and cardiovascular centres in the medulla

Question 17

What are the three features of Cushing’s Reflex?

Answer 17

Hypertension

Bradycardia

(medulla ischaemia activates SNS > hypertension detected by baroreceptors and slows HR)

Bradypnoea
(± irregular)

Question 18

How can the causes of rasied ICP be characterised into 4 groups?

Answer 18

CSF

Brain Tissue

Blood

Other

Question 19

Give 3 examples of causes of raised ICP

Answer 19

Hydrocephalus

Intracranial Haemorrhage

Intracerebral Abscess

(CSF Outflow Obstruction)

Question 20

What is the most common cause of raised ICP?

Answer 20

Traumatic Brain Injury

Question 21

How does the osmolarity of plasma differ from the cerebrospinal fluid?

Answer 21

CSF is HYPEROSMOLAR compared to plasma

(143 mEq/L vs. 138mEq/L)

Question 22

Outline the flow of CSF throughout the brain?

Answer 22

lateral ventricles > interventricular foramen > third ventricle > cerebral aqueduct > fourth ventricle > median & lateral appertures, central canal

Question 23

Which artery provides the blood supply for the lateral ventricle choroid plexus?

Answer 23

internal carotid artery

Question 24

How does the CSF get reabsorbed from the subarachnoid space?

Answer 24

arachnoid villi extend into the dural venous sinuses

CSF moves across villi and is reabsorbed back into the venous circulation

Question 25

What is the difference between a communicating and non-communicating hydrocephalus?

Answer 25

Non-Commnicating

obstruction of CSF flow within or between the ventricles

Communicating
due to excess CSF production or obstructed venous drainage

(no obstruction of CSF flow within or between ventricles - there IS communication between ventricles)

Question 26

What is the most common cause of brain malignancy in adults?

Answer 26

metastatic disease

Question 27

What is idiopathic intracranial hypertension and which population of people is commonly affected?

Answer 27

raised ICP with no identifiable abnormality
(e.g. no mass or hydrocephalus)

obese young women commonly affected

Question 28

How can raised ICP caused by the following be rectified:

Hydrocephalus

Abscess

Tumour

Answer 28

Hydrocephalus
(ventriculoperitoneal shunt)

Abscess
(antibiotics / inscision & drainage)

Tumour
(resection)

Question 29

What are common steps in the management of raised ICP?

Answer 29

ABCDE approach

30 degree head up

IV mannitol / hypertonic saline

intubate and ventilate
(target CO₂ between 4 - 4.5 kPa)