Raised Intracranial Pressure

Question 1

Describe how intracranial pressure is regulated normally

Answer 1

• Normal intracranial pressure usually 5-15mm Hg and can be measured using a manometer
• Autoregulation through vasoconstriction and vasodilation
• Chemoregulation through vasodilation in response to low cerebral pH
  - Increase blood to oxygenate area

Question 2

Describe how intracranial pressure is regulated in the presence of a tumour

Answer 2

• CSF and venous blood volume can decrease to attempt to maintain intracranial pressure when there are other occupants within the fixed volume of the cranium
• Can only compensate to a certain degree - if mass is too big then ICP will rise

Question 3

Describe the pathophysiology of raised intracranial pressure

Answer 3

• A reduction in blood supply to brain cells occurs due to compression by intracranial tumour
  
  • Oxygen required to produce ATP and maintain Na/K ATPase
• Leads to increase in Na concentration inside the cell, thus causing water accumulation
• This is known as cytotoxic cellular oedema, where cells swell and eventually burst
• Swelling causes further compression of blood vessels, which further decreases oxygen supply to brain cells

Question 4

List the signs and symptoms of raised intracranial pressure

Answer 4

• Headache
• Vomiting
• Visual disturbances
• Depression of conscious level
• Increasing head size in infants

Question 5

Describe the pathophysiology behind headaches in raised ICP

Answer 5

• Generalised, progressive ache
• Worse on awakening in the morning - by laying down, increased venous circulation in head causes increased pressure
  
  • Hypoventilation also decreases removal of CO2, thus increasing CO2 levels leading to venodilation which increases pressure
• Aggravated by coughing or sneezing
  
  • Coughing increases intrathoracic pressure, which compresses SVC and stagnates venous flow from head

Question 6

Describe the different visual disturbances seen in raised ICP

Answer 6

• Blurring - compression of optic nerve
• Obscurations - transient blindness upon bending or posture changes
• Papilloedema - defined as optic disk swelling secondary to a rise in intracranial pressure
  
  • Optic nerve has CSF around it, this shifting CSF compresses optic nerve and causes optic disk swelling
• CN VI palsy - problem with lateral rectus muscle
  
  • Originates and hooks around pons
  • First nerve to be compressed in high ICP as it runs close to skull
• Retinal haemorrhages if the rise in ICP has been rapid

Question 7

State the types of herniation syndromes in raised ICP

Answer 7

• Subfalcine herniation
• Uncal herniation
• Tonsillar herniation

Question 8

Describe subfalcine herniations

Answer 8

• Most common
• Asymptomatic but could have headaches and contralateral leg weakness if anterior cerebral artery compressed
• Midline shift on CT

Question 9

Describe uncal herniation

Answer 9

• Uncus displaced across tentorial opening
• As the herniation progresses, the uncus puts pressure on the midbrain
  
  • Ipsilateral oculomotor nerve - ipsilateral dilated pupil due to loss of parasympathetics along CN III
  • Compression of cerebral peduncle - contralateral motor weakness
  • Decreased level of consciousness - compress reticular formation within brainstem

Question 10

Describe tonsillar herniation

Answer 10

• Cerebellar tonsils herniate through the foramen magnum
  
  • Compression of medulla and upper spinal cord
  • Brainstem affected - cardiac and respiratory dysfunction
  • Decreased level of consciousness

Question 11

Describe Cushing’s reflex and its presentation

Answer 11

• Occurs if raised ICP is not treated and continues to rise, leading to destruction of the brainstem
• Triad - high blood pressure, bradycardia, low respiratory rate (opposite to septic patient)
• If untreated, leads to death

Question 12

Describe the pathophysiology of Cushing’s reflex

Answer 12

• Ischaemia at medulla -> sympathetic activation -> rise in blood pressure + tachycardia -> baroreceptors react -> bradycardia
  
  • When oxygen taken away, sodium levels within the cell rise due to loss of Na/K - leading to sympathetic activation
• Ischaemia at pons/medulla at respiratory centres -> low respiratory rate
  - Increased firing of vagal neurones

Question 13

Describe the causes or raised ICP

Answer 13

• Increased cerebral blood volume
  
  • Venous outflow obstruction
  • Venous sinus thrombosis
• Cerebral oedema
  
  • Meningitis, encephalitis
  • Diffuse head injury
  • Infarction
• Increased CSF
  
  • Impaired absorption - hydrocephalus, benign intracranial hypertension
  • Excessive secretion - choroid plexus papilloma
• Expanding mass (space occupying lesions)
  
  • Abscess
  • Tumour
    
    • Haemorrhage / haematoma

Question 14

Define hydrocephalus

Answer 14

Accumulation of CSF due to imbalance between production and absorption of CSF leading to enlargement of brain ventricles

Question 15

Describe non-communicating hydrocephalus

Answer 15

• Non-communicating/obstructive - CSF is obstructed within the ventricles or between the ventricles and subarachnoid space
• Most commonly due to aqueduct block
• Also due to tumours - eg. Meningioma

Question 16

Describe communicating hydrocephalus

Answer 16

• Communicating - there is communication between the ventricles and the subarachnoid space
• Reduced absorption or blockage of the venous drainage system
• Mostly due to post-meningitis - bacterial, fungal, TB
• Subarachnoid haemorrhage
• Can also be due to trauma or tumour of subarachnoid space
• Increased CSF production - choroid plexus papilloma

Question 17

Describe the type of brain tumours commonly seen

Answer 17

• Most common due to metastasis
• Most common in children and elderly
• Brain tumours are the second most common childhood cancer after leukaemia
  
  • Astrocytomas - from astrocytes
  • Medulloblastomas - from neuroectodermal cells
• In adults - gliomas, meningiomas
  
  • Metastases - from lung, breast and kidneys
• Tend to be midline or posterior region

Question 18

Describe idiopathic intracranial hypertension including investigation and treatment

Answer 18

• Raised intracranial pressure without evidence of hydrocephalus or mass lesion
• Normal investigations including imaging of brain but signs or raised ICP
• Treatment - weight loss, carbonic anhydrase inhibitors, CSF drainage, shunts

Question 19

Describe the management of raised ICP due to increased cerebral blood volume or cerebral oedema

Answer 19

• Do not do lumbar puncture - brain can be drawn out of skull due to release of CSF
• Increased cerebral blood volume (venous flow obstruction, venous sinus thrombosis)
  
  • Anticoagulation
• Cerebral oedema (infection, head injury, infarction)
  
  • Treat the cause
  • Mannitol - osmotic agent to make the plasma more osmotic than CSF, therefore fluid flows into the blood and out of the brain

Question 20

Describe the management of raised ICP due to increased CSF or mass present

Answer 20

• Do not do lumbar puncture - brain can be drawn out of skull due to release of CSF
• Increased CSF (hydrocephalus, choroid plexus papilloma)
  
  • Shunts - ventricles down spinal cord to peritoneum
  • Tumour resection
  • Use diuretics whilst awaiting intervention
    
    • Furosemide, carbonic anhydrase inhibitors - drain excess water out of circulation to prevent recirculation back to head
• Tumour, haemorrhage, abscess
  
  • Surgical resection - craniotomy
  • Steroids for tumours