🎯 Pathology

• increased pressure within the cranial cavity

• the cranium is akin to a rigid box that accommodates 3 main components

  • brain

  • cerebrospinal fluid (CSF)

  • blood

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🧠 Monro-Kellie doctrine

• the Monro-Kellie doctrine explains the relationship between intracranial content (brain, blood and CSF) and intracranial pressure (ICP)

• it states that the intracranial volume is fixed (like a rigid box), although in the presence of a space-occupying lesion (e.g. a mass) which leads to an increase in ICP, the ICP may be compensated for by the displacement of:

  • CSF into the spinal cord, or

  • venous blood into the circulation

• the ICP will rise at the point of decompensation

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🧐 Calculation of cerebral perfusion pressure (CPP)

• CPP = mean arterial pressure (MAP) - intracranial pressure (ICP)

• normal ICP in adults = 7-15 mmHg

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⬆️ Consequences of raised ICP

1. if ICP rises, the perfusion of blood to brain tissue decreases —> death of brain tissue due to ischaemia

2. brain herniation —> comatose and death

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💡 Causes

• idiopathic intracranial hypertension

• mass

  • tumour, abscess, haematoma

• increased CSF

  • hydrocephalus

• increased blood volume

  • venous sinus thrombosis

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🩺 Clinical features

• headache (worse in the morning and with Valsalva maneouvre)

• nausea and vomiting

• visual changes

  • bilateral or unilateral horizontal double vision (due to involvement of CN VI)

  • papilloedema may be seen on fundoscopy

  • unilateral or bilateral esotropia (due to involvement of CN VI)

  • vision loss

• Cushing triad (a sign of impending herniation)

  • hypertension

  • bradycardia

  • irregular respiration

• a bulge over the anterior fontanelle in infants

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🕵️‍♂️ Investigations

• CT/MRI brain

• fundoscopy to investigate for papilloedema

• monitoring of ICP

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💆‍♂️ Management

• elevation of head of bed to > 30 degrees

• maintain neck in the midline to help with venous drainage from the head

• controlled hyperventilation

  • this reduces the PaCO2 which promotes vasoconstriction of the cerebral arteries thereby reducing the ICP

• osmotic diuretics: IV manitol

• 3% hypertonic saline

• removal of CSF via

  • external ventricular drain

  • ventriculoperitoneal shunt

  • lumbar puncture

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🧲 High-yield tips

• a lumbar puncture is absolutely contraindicated in a case of any space-occupying lesion as it may precipitate coning (compression of the brainstem which is a neurosurgical emergency)

  • always get a brain CT prior to performing a lumbar puncture

• CN VI nerve is the first cranial nerve to be affected by a raised ICP