What is raised ICP? Types?
This is raised pressure in the cranial cavity Chronic or acute
Causes of raised ICP?
Increased pressure in fluid around brain (CSF) or increased pressure within brain itself
- Brain Tumour
- Head injury
Is raised ICP a medical emergency? If yes, why?
Yes Because it can cause damage to the brain, spinal cord and the eyes
Describe the components of ICP?
ICP is the sum of:
Describe how the ICP is kept constant?
If one component increases, the others decrease to compensate and keep the ICP constant (and vice versa)
Describe the monro-kellie hypothesis?
If one component of ICP increases, the others decrease the compensate and keep the ICP constant (and vice versa)
Describe the cranial cavity in regards to ICP?
The cranial cavity is an enclosed space and is unable to expand as the pressure increases
Describe the relationship between ICP and volume?
As volume increases, compensatory mechanisms are able to prevent the pressure from rising After compensatory mechanism fail, a small change in volume will cause a large change in pressure (exponential)
Increased pressure can lead to damage Give examples?
Damage to tissue
Shifts to tissue
Damage to brain, spinal cord and eye
Constriction of blood vessels
Describe a statistic that links raised ICP and visual symptoms?
65% of patients with ICP will complain of some visual symptoms
Examples of visual symptoms caused by raised ICP?
Transient Blurred Vision Doubled Vision Loss of Vision Papilloedema (Swelling of optic discs due to raised ICP) Pupillary changes Can affect one eye or both
Optic nerves are not actually nerves but they are...?
What covers optic nerves?
3 Meninges: - Dura - Arachnoid - Pia
What is the space between the Arachnoid and Pia called?
What are meninges?
These are the three membranes than envelope the brain and the spinal cord - they are the protective coverings
Describe the Dura Mater? Sensory supply?
This is the tough, outer meningeal layer Sensory supply is CN V Encloses dural venous sinuses
Describe the arachnoid mater?
This is the spidery mother Has lots of little projections called 'arachnoid granulations'
Describe the subarachnoid space?
This is space below the arachnoid mater There is circulating CSF and blood vessels
Describe the pia?
This is the faithful mother Adheres to the brain Also adheres to vessels and nerves that are entering/leaving the brain
Label this diagram?
A = Pia B = Arachnoid Layer C = Dura D = Dura
How do you access the subarachnoid space?
Lumbar puncture between L3/L4 or L4/L5
Where does the subarachnoid space end?
At the level of S2 (Part of the Sacrum)
Label this diagram?
A = Subarachnoid Space B = Dura C = Arachnoid D = Pia
The subarachnoid space communicates with another series of CSF filled spaces in the brain. What are these called?
Name the ventricles of the brain?
3rd 4th Left Lateral Right Lateral
Label this diagram?
A = Third Ventricle B = Left Lateral Ventricle C = Right Lateral Ventricle D = Subarachnoid Space E = Central Canal of the Spinal Cord F = 4th Ventricle G = The Cerebral Aqueduct H = Pituitary Gland I = Optic Chiasm J = Sinus
Describe the circulation of CSF?
1. Produced by the choroid plexus of both lateral ventricles 2. Passes into the third ventricle 3. Goes via the cerebral aqueduct into the fourth ventricle 4. Passes into subarachnoid space 5. Some goes into central canal of spinal cord 6. Most is reabsorbed from the subarachnoid space by the arachnoid granulations 7. Reabsorbed into the dural venous sinuses
Describe how raised ICP is transmitted?
This is transmitted along the subarachnoid space of the optic nerve sheath
Describe how raised ICP leads to swollen discs?
Raised ICP compresses the optic nerve It also compresses the central retinal artery and vein This leads to bulging, swollen discs
Describe damage to CN III?
This is susceptible to damage (Eg: Compression) Leads to the eye being 'down and out' with a dilated pupil
Oculomotor nerve damage causes the eye to be in what position?
Down Out Dilated pupil
Describe herniation/raised ICP?
Raised ICP can compress/stretch oculomotor nerve if medial temporal lobe herniates through tentorial notch
Describe damage to the trochlear nerve (CN IV)?
This has a long intracranial course and is susceptible to injury: - Stretching - Compression Results in superior oblique paralysis Eye cannot move inferior
Describe damage to CN VI? (Abducens)
Long intracranial course and is susceptible to stretching Results in lateral rectus paralysis Eye cannot move laterally