Space Occupying Lesions & Pseudotumour Cerebri (idiopathic intracranial hypertension)

Question 1

What can cause localised swelling of the brain?

Answer 1

Local infarction
Local inflammation (abscess)
Neoplasia
Trauma
Vascular local haemorrhage

Question 2

What can raise intracranial pressure [>2kPa]

Answer 2

Generalised brain swelling
Generalised infections (meningitis)
Metabolic (hypoglycaemia, hepatic encephalopathy)
Hypoxia
Hypotension

Question 3

What mechanisms cause brain swelling?

Answer 3

1. Mass lesion (eg bleed)
2. Vasodilation (local or general)
3. Cerebral oedema (local or general)

Question 4

What are the mechanisms of cerebral oedema?

Answer 4

1. Vasodilation
2. Vasogenic oedema

Due to;

1. Crytotoxic - injury..
2. Interstitial oedema - hydrocephalus & leakage of ventricular lining

Question 5

Outline the series of events from cerebral volume increase to raised intracranial pressure

Answer 5

1. Low CSF space [compensation..]
2. Pressure atrophy
3. Low blood volume in sinuses
4. Critical volume with failure of compensatory menchanism
5. Abrupt increase in ICP
   - Shifting brain structure + herniation & compression
   - Cerebral vessels compressed
   - Ischaemia induced brain swelling & necrosis

Question 6

Outline the common places for herniation & their effects

Answer 6

1. Transalvarial [pops out of skull]
   - Motor/ sensory deficit depending on where
2. Subfalcine [longitudinal fissue down the centre]
   - Occludes MCA [infarction]
   - Cingulate gyrus squashed [abnormal posture]
3. Transtentorial [down into cerebellum]
   - CN3, 6
   - PCA
   - Brainstem [cardio-resp depression]
4. Tonsilar [cerebellum pops down into spine]
   - Brainstem/ medulla compressed
   - Basillar artery
   - CSF compression

Question 7

Why does raised ICP cause vomiting

Answer 7

Compression of vomiting centres in medulla

Question 8

Why does raised ICP cause headache

Answer 8

Increased pressure stimulated pain receptors

Question 9

Why does raised ICP cause Papilloedema

Answer 9

Inc CSF pressure transmitted to optic nerve, causing low flow of axonal cytoplasm in optic nerve

Question 10

Why does raised ICP cause dilation of pupil

Answer 10

CN3 compression

Question 11

Why does raised ICP cause variation in consciousness

Answer 11

Compression of brain stem & reticular activating system

Question 12

Why does raised ICP cause bradycardia

Answer 12

Baroreceptor activation

Compresses regulatory centres in medulla

Question 13

Why does raised ICP cause hypertension

Answer 13

Low cerebral blood flow activates thalamus

Inc sympathetic

Question 14

Why does raised ICP cause neruogenic pulmonary oedema

Answer 14

Sympathetic activity inc hypostatic pressure?