Intracranial pressure

Question 1

What 3 categories of disease can cause raised intracranial pressure?

Answer 1

1. Intracranial masses (either intrinsic such as a tumour or extrinsic such as a subdural haematoma).
2. Diffuse brain swelling following severe hypoxia, liver failure or hypertensive encephalopathy.
3. Impaired circulation or absorption of CSF (can also be due to a rare tumour in the CSF-producing choroid plexus.

Question 2

What is seen on imaging when raised ICP is due to CSF?

Answer 2

Enlarged ventricles

Hydrocephalus

Question 3

What are the causes for impaired reabsorption of CSF?

Answer 3

Thrombosis in the sagittal sinus
Increased venous pressure gradient across the arachnoid villi
Function of arachnoid villi is damaged by the contents of the CSF e.g. in chronic meningitis.

Question 4

What are the symptoms of raised intracranial pressure?

Answer 4

Headache (worse in the morning/lying flat)
Ataxia
Drowsiness
Confusion
Coma
Papilloedema (seen in chronic not acute)
Cranial nerve 6 palsy
Cranial nerve 3 palsy

Question 5

Which cranial nerves are most likely to be damaged with raised ICP? What are the symptoms?

Answer 5

Cranial nerve 6 is usually the first to be effected - patient cannot abduct their eyes because this nerve innervates the lateral rectus muscle.
Cranial nerve 3 is also affected in temporal lobe herniation (looking down and out when it is, also ptosis, dilated pupils)
Both cause double vision.

Question 6

What is the principle cause of low ICP? What causes this?

Answer 6

CSF leakage through torn meninges.

Trauma, tumour, iatrogenic (lumbar puncture)

Question 7

What are the symptoms of low ICP?

Answer 7

Headache (worse on standing, improved on lying flat). 
CSF rhinorrhoea (leakage from nose associated with recurrent meningitis). 
May develop false localising signs such as cranial nerve 6 palsy.

Question 8

What are the 2 main sites of cerebral herniation and what are the 3 types of herniation?

Answer 8

Sites: tentorium cerebri and foramen magnum.

Types:

1. Asymmetrical tentorium herniation (uncus of the temporal lobe herniates through)
2. Symmetrical tentorium herniation (from the top)
3. Foramen magnum herniation

Question 9

What are the complications of an asymmetrical tentorium herniation?

Answer 9

Compression of:

1. 3rd CN - leading to 3rd nerve palsy
2. Midbrain - leading to coma and pupillary changes bilaterally with a tetraparesis
3. Posterior cerebral artery - leading to occipital infarction, increasing supratentorial pressure and increasing herniation.

Question 10

What are the complications of an a symmetrical tentorium herniation?

Answer 10

Produces compression of the whole of the midbrain because it comes from directly above rather than from the side like asymmetrical herniation.
This causes bilateral dilated pupils, coma and tetraparesis.

Question 11

What are the symptoms and signs of foramen magnum herniation?

Answer 11

Compression of the reticular formation, respiratory centres and motor tracts. This leads to severe neck pain, erratic breathing, progressing tetraparesis and coma.

Question 12

What are the treatment options for raised ICP?

Answer 12

Treatment depends on the cause.
Surgical treatment for subdural/extradural haematomas or hydrocephalus.
Mannitol (osmotic diuretic) can be used short term in those with brain swelling.
Steroids will reduce cerebral oedema but not cytotoxic oedema (result of dying cells).
Hyperventilation in ventilated patients will reduce cerebral oedema.
In some circumstances, surgical decompression can be used.