The three hallmarks over raised ICP:
- Headaches- worse in the morning, aggravated by bending, stooping
- Vomiting- occurrs acute rise in ICP, due to activation of the vomiting centre area postrema
- Papilloedema- the optic nerve runs within the optic sheath, raised ICP impairs venous outflow and results in swelling
This diagram is explains everything beautifully. When a nurse comes and tells you hey doc this patient has blown a pupil here is why! It is a sign of significantly raised ICP.
Effects of a Lateral tentorial herniation (temporal lobe herniates through the tentorial notch occupying the midbrain)
- Depressed Level of Consciousness due to interrupation of the reticular activating formation governing consciousness
- Compression of the 3rd nerve nucleus in the midbrain leading to 3rd nerve palsy
- Contra-lateral homonymous hemianopia due to compression of the posterior cerebral artery
- Ipsilateral Hemiparesis this is due to compression of Kernohans notch. This is compression of the cerebral peduncles (white matter conducting the longer fibre tracts)
Note the corticospinal tracts decussate above the pyramid hence any weakness will be contra-lateral and ipsilateral weakness is a false localising sign.
The effects of a central tentorial herniation can cause the following:
- Impaired upward gaze due to pressure on the superior collicus effecting upward gaze centres
- Tonsillar hernation due to progression compression
- Diabetes insipidus due to compression on the pituitary stalk
- Fixed and dilated pupil
Cerebellar tonsils herniate through the foramen magnum. This can lead to significant effect on the respiratory and cardiac centres leading to irregular respiratory rate.
The famous Cushing’s Triad:
Herniation of the cingulate gyrus under the falx cerebri. Compression of the anterior cerebral artery leading to contra-lateral leg weakness.