Raised intracranial pressure
How a fixed skull holds brain, blood and cerebrospinal fluid in balance, why masses, swelling or blocked CSF raise the pressure once compensation runs out, and how falling blood flow and herniation of brain tissue become life-threatening.
By the end, you can
- Describe the contents of the skull and how CSF is made, circulates and is absorbed.
- Explain the Monro-Kellie principle and how the skull compensates for an added volume.
- Explain cerebral perfusion pressure and the vicious cycle of raised pressure, ischaemia and swelling.
- Describe the main herniation patterns and the signs each produces.
- Relate headache, vomiting, papilloedema and falling consciousness to raised pressure.
- Recognise the classic herniation pathology (Kernohan’s notch, Duret haemorrhages), the key pressures and tests of raised intracranial pressure, and explain how the main treatments lower pressure or protect perfusion.
What it is
Raised intracranial pressure is pressure inside the skull above the normal range (about 7 to 15 mmHg lying down in adults), caused when the volume of the skull’s contents increases. Because the adult skull cannot expand, sustained rises reduce blood flow to the brain and can push brain tissue across rigid barriers (herniation).
4 types to tell apart
- Mass lesion
- Tumour, haematoma, abscess.
- Brain swelling (oedema)
- Head injury, stroke, infection, liver failure, low sodium.
- CSF build-up (hydrocephalus)
- Blocked flow or failed absorption of cerebrospinal fluid.
- Idiopathic intracranial hypertension
- Raised pressure without a mass or hydrocephalus, mostly in young women with obesity; threatens vision.
Normal function
A fixed box with three contents
The adult skull is a rigid box holding brain tissue (about 80% of the volume), blood (about 10%) and cerebrospinal fluid (CSF, about 10%). The Monro-Kellie principle states that their total volume is fixed: if one increases, another must decrease or the pressure rises.
CSF is made mainly by the in the ventricles, flows from the to the , through the narrow to the , then around the brain and spinal cord before being absorbed into the venous sinuses.
Blood flow to the brain depends on cerebral perfusion pressure: mean arterial pressure minus intracranial pressure. Brain vessels adjust their diameter (autoregulation) to keep flow steady across a range of pressures.
| Feature | Share of volume | Can it be displaced? |
|---|---|---|
| Brain tissue | About 80% | No |
| Blood | About 10% | Venous blood can be squeezed out |
| CSF | About 10% | Can move into the spinal canal |
Underlying change · Step 1 of 4
Something adds volume
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 2 of 4
Compensation runs out
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 4
Brain tissue is pushed across barriers
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 4 of 4
Headache, vomiting and falling consciousness
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 4 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .