ICP/CPP

Question 1

What is the Munro-Kelly doctrine?

Answer 1

Cranium is rigid structure
Contains brain, blood, CSF
Increase in mass must result in compensatory change in blood/CSF volume to maintain correct ICP

Question 2

What can cause raised ICP?

Answer 2

Localised lesions

• haemorrhage
• tumour
• abscess

Oedema post-trauma

Question 3

What is CPP and what does it equate to? What is the relevance to raised ICP?

Answer 3

Cerebral perfusion pressure
= MAP - ICP

Raised ICP leads to reduced perfusion
- ischaemia can cause infarction of brain tissue

Question 4

At what level does raised CPP become problematic and why?

Answer 4

When CPP exceeds 150mmHg

Exudation from vasculature causes oedema

Question 5

What factors can affect autoregulation of CPP?

Answer 5

CO2, toxins causing vascular dilatation

Head trauma

Question 6

What are the symptoms of raised ICP?

Answer 6

Morning headache/sickness - cortex/brain squeeze
Visual disturbances (diplopia, blurred vision)
Cognitive impairment
Decreased GCS
Papilloedema
3rd/6th nerve palsies
Brainstem death - cerebellum squeezing down, crushing brainstem

Question 7

What is Cushing’s reflex? Why does it happen?

Answer 7

Vasopressor response to raised ICP, causing:
Hypertension, irregular breathing and bradycardia (Cushing’s triad)

Increased ICP more than MAP
Compression of cerebral arterioles
Decreased CBF, activation of ANS
Sympathetic response - alpha1 adrenergics > hypertension, tachycardia
Resultant increased pressure stimulates aortic baroreceptors, which stimulate vagus > bradycardia
Bradycardia also due to mechanical distortion of medulla

Question 8

How might ICP be managed?

Answer 8

Head elevation to facilitate venous return
Mannitol/hypertonic saline
Hyperventilation - decrease CBF (temporary)
Barbiturate coma - decrease cerebral metabolism, CBF
Surgical decompression

Newer concepts

• Brain tissue oxygenation monitoring
• micro-dialysis, investigate brain metabolism

Question 9

What is hydrocephalus? What are the types?

Answer 9

Increased fluid in the brain

• obstructive (blockage of outflow from ventricles)
• communicating (block at level of arachnoid granulations)

Question 10

What are the risk factors/causes of hydrocephalus?

Answer 10

Congenital

• Chiari malformation
• aqueductal stenosis
• Dandy-walker malformation

Acquired

• meningitis
• post-haemorrhagic
• neoplastic (benign/malignant)
• post-op (especially for posterior fossa surgery)
• cerebellar stroke
• post-traumatic

Question 11

What are the symptoms/signs of hydrocephalus in infants?

Answer 11

Cranial enlargement
Splaying of cranial features
Irritable, poor feeding
Fontanelles full and bulging
Engorged scalp veins
Abducens palsy
Perinaud's syndrome
Exaggerated reflexes
Respiratory problems

Question 12

What are the symptoms/signs of hydrocephalus in adults/older children?

Answer 12

May be asymptomatic
Increased ICP
Headaches (worse in morning and coughing)
Papilloedema
Visual disturbances
Gait abnormality
Loss of upgaze/abducens palsy
Impaired consciousness

Intracranial mass symptoms if cause

Question 13

What investigations might be done in suspected hydrocephalus?

Answer 13

LP if intracranial mass not suspected

CT/MRI/biopsy if mass is suspected

Question 14

What may be some differential diagnoses of hydrocephalus?

Answer 14

Normal pressure hydrocephalus

Idiopathic intracranial hypertension

Question 15

What is the treatment for hydrocephalus?

Answer 15

Acetazolamide - carbonic anhydrase inhibitor - reduces CSF
External ventricular drain in emergency
Eliminate obstruction
Shunt/ventriculostomy (3rd:subarachnoid spaces, only in non-communicating)

Question 16

What is normal pressure hydrocephalus? Signs/symptoms/treatments?

Answer 16

Increased CSF but with seemingly normal pressure on LP
Classical triad
- dementia
- gait disturbance ('magnetic gait')
- urinary incontinence

Age >60
Communicating hydrocephalus
Improvement after shunt

Question 17

What is idiopathic intracranial hypertension? Signs/symptoms/treatments?

Answer 17

Raised ICP without obvious cause
Typical patient young obese female
Often presents with headaches and visual disturbances - can go blind
Treatment
- weight loss (6% of weight)
- acetazolamide
- CSF diversion - VP or LP shunt
- optic nerve sheath fenestration

Also termed benign intracranial hypertension/pseudotumour cerebri

Question 18

What are some complications of shunt placement?

Answer 18

Over-drainage - low pressure headaches, subdural haematoma
Under-drainage
Blockage
Infection
Disconnection
Seizures
Distal-end problems - hernias, arrhythmias

Question 19

When is an LP indicated and contraindicated?

Answer 19

Indicated

• obstain CSF for analysis
• measurement of ICP
• drainage for raised pressure (if obstructive ruled out)
• diagnostic for normal pressure hydrocephalus

Contraindications

• skin infection near LP site
• suspicion of raised ICP due to mass
• uncorrected coagulopathy
• acute spinal cord trauma

Question 20

What checks should be done pre-LP?

Answer 20

Awake and conscious patient
No focal neurological deficit (6th nerve palsy)
If CT/MRI rule out intracranial mass
Ensure no anticoagulants

Question 21

What care should be given post-LP?

Answer 21

Bed rest for 2-4 hours
Warn about low pressure headaches
Stop if patient develops neurological deficit or becoming unconscious
Think of herniation syndromes
Head down/feet up
CT brain for subdural haematoma if no improvement
Urgent MRI if concerned about epidural haematoma

Question 22

What are the different types of herniation syndrome?

Answer 22

Cingulate
Central
Uncal
Cerebellotonsillar
Upward
Transcalvarial

Cerebellar tonsillar herniation = cause of brainstem death
- tonsils move inward and downwards, crushing brainstem

Question 23

What analysis may be performed on CSF after LP and what might the findings suggest?

Answer 23

Analysis

• rule out bacterial/viral infection
• measure for blood breakdown products (SAH)
• measure protein load
• test for others

In meningitis

• cloudy, turbid
• high WCC, mostly polymorphs
• protein >1g/L
• low glucose

Bloody CSF

• traumatic tap
• following SAH

Yellow CSF

• xanthrochromatic
• yellow due to blood breakdown products
• most common in SAH
• CSF spectrophotometry for bilirubin (SAH) - positive only after 12hr, persists for 3w

Question 24

Risks in performing an LP?

Answer 24

Bleeding
Infection
Nerve root injury
Retroperitoneal/intra-abdominal injury
Brainstem herniation