S10) Pathophysiology and Management of Raised Intracranial Pressure

Question 1

What is normal intracranial pressure?

Answer 1

Normal ICP = 5–15 mm Hg (7–20 cm H₂O)

Question 2

What are the occupants of intracranial space?

Answer 2

• CSF
• Blood
• Neural tissue (brain + spinal cord)

Question 3

In a healthy individual, the blood flow to the brain is regulated.

Explain how this occurs by autoregulation and chemo-regulation?

Answer 3

• Autoregulation – vasoconstriction, vasodilation
• Chemo-regulation – vasodilation in response to low cerebral pH e.g. high pCO₂

Question 4

Illustrate the intracranial compensation for an expanding mass

Answer 4

Question 5

In four steps, illustrate the pathophysiology of a brain injury

Answer 5

Question 6

Identify four signs of symptoms of raised intracranial pressure

Answer 6

• Headache
• Vomiting
• Visual disturbances
• Depression of conscious level

Question 7

Describe five characteristics of a headache due to raised ICP

Answer 7

• Generalised ache
• Worst on awakening in the morning
• May awaken patient from sleep (due to hypoventilation in sleep)
• Aggravated by bending, stooping, coughing or sneezing
• Severity gradually progresses

Question 8

Describe four characteristics of visual disturbances due to raised ICP

Answer 8

• Blurring
• Obscurations – transient blindness upon bending or posture changes
• Papilloedema (some patients)
• Retinal haemorrhages (if rapid ICP rise)

Question 9

Identify two red flag signs of raised ICP

Answer 9

• Papilloedema
• CN VI palsy – false localising sign

Question 10

Describe the occurrence and presentation of a subfalcine herniation

Answer 10

• Most common
• May be asymptomatic
• Symptoms incl. headache, contralateral leg weakness (if, ACA affected)
• Midline shift on CT

Question 11

What is an uncal herniation?

Answer 11

An uncal herniation is when the uncus, the medial part of the temporal lobe, is displaced across the tentorial opening

Question 12

As the herniation progresses, the uncus puts pressure on the midbrain.

Describe the different possible presentations of uncal herniations

Answer 12

• Decreased level of consciousness
• Compressed ipsilateral oculomotor nerve – ipsilateral dilated pupil
• Compressed cerebral peduncle – contralateral leg weakness

Question 13

What is a tonsillar herniation?

Answer 13

A tonsillar herniation is when the cerebellar tonsils herniate through the foramen magnum

Question 14

Explain the presentations of tonsillar herniations?

Answer 14

Compression of medulla and upper spinal cord:

• Brainstem affected – cardiac and respiratory dysfunction
• Decreased level of consciousness

Question 15

What is Cushing’s reflex?

Answer 15

- Cushing reflex is a physiological nervous system response to untreated raised ICP

• It is a poor prognostic sign consisting of the following triad: high BP, bradycardia, low RR

Question 16

In five steps, explain how bradycardia and hypertension occur due to raised ICP

Answer 16

⇒ Ischaemia at medulla

⇒ Sympathetic activation

⇒ Rise in blood pressure & tachycardia

⇒ Baroreceptors react

⇒ Bradycardia

Question 17

In two steps, explain how hypoventilation occur due to raised ICP

Answer 17

⇒ Ischaemia at pons/medulla at respiratory centres

⇒ Low respiratory rate

Question 18

Identify and describe the four causes of raised intracranial pressure

Answer 18

• Increased cerebral blood volume – venous outflow obstruction, venous sinus thrombosis
• Cerebral oedema – meningitis, encephalitis, diffuse head injury, infarction
• Increased CSF – impaired absorption (hydrocephalus), excessive secretion (choroid plexus papilloma)
• Expanding mass / SOL – abscess, tumour, haematoma

Question 19

What leads to the clinical suspicion of raised ICP?

Answer 19

• Traumatic brain injury (haemorrhages, anticoagulants)
• Severe meningitis encephalitis
• Risk factors, signs and symptoms of cancer
• CVS risk factors

Question 20

Describe the composition and appearance of cerebrospinal fluid

Answer 20

• Normal CSF is clear and colourless
• It contains very little protein (15 to 45 mg/dL), little immunoglobulin, and only 1-5 cells (leukocytes) per ml
• It is hyperosmolar compared to plasma

Question 21

Where is CSF produced?

Answer 21

The choroid plexus

Question 22

Briefly describe the pathway of CSF flow

Answer 22

Question 23

What is hydrocephalus?

Answer 23

Hydrocephalus is the accumulation of CSF due to an imbalance between the production and absorption of CSF with subsequent enlargement of brain ventricles

Question 24

Identify and describe the two types of hydrocephalus

Answer 24

• Non-communicating/obstructive – CSF is obstructed within the ventricles or between the ventricles
• Communicating – there is communication between the ventricles and the subarachnoid space

Question 25

A communicating hydrocephalus occurs when there is communication between the ventricles and the subarachnoid space. Discuss the possible causes

Answer 25

**Problem lies outside of the ventricular system:** - Due to reduced absorption or blockage of the **venous drainage system** - May also be due to **increased CSF production** the subarachnoid space - Mostly due to **post-meningitis** (bacterial, fungal, TB) - Also due to **trauma + neoplastic infiltration** of subarachnoid space

Question 26

A non-communicating/obstructive hydrocephalus occurs when the CSF is obstructed within the ventricles or between the ventricles and the subarachnoid space. Discuss its possible causes

Answer 26

- Most commonly due to **aqueduct blockade** - Can be **congenital** or **acquired** - May be due to **tumours** *e.g. meningioma*

Question 27

What are the two age peaks for brain tumours?

Answer 27

- In children - In late middle age

Question 28

What are the most common types of brain tumours in children?

Answer 28

- **Astrocytomas** from astrocytes - **Medulloblastomas** from neuroectodermal cells

Question 29

What are the most common types of brain tumours for adults?

Answer 29

- Gliomas - Meningiomas - Metastases from lung, breast and kidneys

Question 30

What is idiopathic intracranial hypertension?

Answer 30

- **Idiopathic intracranial hypertension** is raised intracranial pressure without evidence of hydrocephalus or mass lesion - This usually occurs in obese young women after weight gain

Question 31

What are the treatment options for idiopathic intracranial hypertension?

Answer 31

- Weight loss - Drugs *e.g. carbonic anhydrase inhibitors, CSF drainage and shunts*

Question 32

What are the principles of management of raised ICP due to increased cerebral blood volume?

Answer 32

Varies: - Anticoagulation - Rarely, tenting of venous sinuses

Question 33

What are the principles of management of raised ICP due to cerebral oedema?

Answer 33

**Treat the cause:** - Mannitol - Hypertonic saline

Question 34

What are the principles of management of raised ICP due to increased CSF?

Answer 34

- Shunts - Tumour resection - Use diuretics whilst awaiting intervention *e.g. furosemide, carbonic anhydrase inhibitors*

Question 35

What are the principles of management of raised ICP due to space occupying lesions?

Answer 35

- Surgical resection *e.g. craniotomy* - Steroids of high value of brain tumours