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Relevant Anatomy And Contraindications

  1. The intracranial compartment is divided into 3 compartments by 2 major dural structures, the falx cerebri and the tentorium cerebelli.
  2. The tentorium cerebelli divides the posterior fossa or infratentorial compartment (the cerebellum and the brainstem) from the supratentorial compartment (cerebral hemispheres).
  3. The falx cerebri divides the supratentorial compartment into 2 halves and separates the left and right hemispheres of the brain.
  4. Both the falx and the tentorium have central openings and prominent edges at the borders of each of these openings.
  5. When there is a significant increase in ICP, the brain can slide through these openings within the falx or the tentorium, a phenomenon known as herniation.
  6. As the brain slides over the free dural edges of the tentorium or the falx, it frequently is injured by the dural edge.
  7. Several types of herniation exist, as follows: (1) transtentorial herniation, (2) subfalcine herniation, (3) central herniation, (4) upward herniation, and (5) tonsillar herniation.


  1. Herniation of uncus through tentorial hiatus.
  2. Signs:
    1. Compression of 3rd cranial nerve causing ipsilateral dilatation of pupil.
    2. Pyramidal tract compression causes contralateral hemiparesis.
    3. Lateral displacement of the brain stem causing an ipsilateral hemiparesis.
    4. Posterior cerebral artery kinking causing cerebral ischaemia / hemianopia.
    5. Brain stem compression resulting in deterioration of the level of consciousness leading to coma,
    6. Hypertension and bradycardia (Cushing response and respiratory failure, which may be manifested as Cheyne-Stokes periodic breading pattern.

Foramen Magnum

  1. Increased pressure within the posterior fossa will result in herniation of the cerebellar tonsils into the foramen magnum and compression of the medulla.
  2. Signs:
    1. If slowly progressing the patient may develop abnormal neck posture and a child may develop a neck tilt.
    2. Rapid respiratory failure.
    3. May cause abrupt limb paresis and sensory disturbance.
Fig 3.3: Brain Herniations. A lateral supratentorial mass will cause displacement of the lateral ventricles with (1) subfalcine herniation of the cingulated gyrus below the falz cerebri; (2) herniation of the uncus into the rentorial hiatrus; (3) caudal displacement of the brain stem. Raised pressure within the posterior fossa may cause herniation of the cerebellar tonsils into the foramen magnum.
Monro-Kellie Doctrine Q: Simple concept but vital for the understanding of intracerebral pathologies and dynamics. Monro-Kellie doctrine states that the total intracranial volume is fixed because of the inelastic nature of the skull. The intracranial volume (V i/C. is equal to the sum of its components, as follows:
V i/c = V (Brain) + V (CSF) + V (BlooD.

Intracranial Pressure Q

  1. Normal ICP <10mmHg (136 mm water)
  2. 20 mmHg < is abnormal.
  3. 40 mmHg < severe elevation.
  4. The higher the ICP after head injury the worst the outcome
  5. ICP value gets elevated at point of decompensation.
  6. When ICP starts going up the patient will rapidly decompensate and herniation is imminent

Signs of increased ICP Q

  1. Headache:
  2. Nausea and vomiting, usually worse in the morning.
  3. Drowsiness. Important clinical sign not to be dismissed.
  4. Papilloedema.
    1. Due to transmission of the pressure in the subarachnoid sheath to the optic nerve.
    2. “Filling in” of the optic cup and dilatation of the retinal veins.
    3. Failure of the normal pulsations of the retinal veins.
    4. Blurring of the disk margins.
    5. Flame shaped haemorrhages along disk margins and alongside the vessels.
    6. Optic atrophy may develop in long standing raised ICP.
  5. 6th nerve palsy, causing diplopia may occur in raised ICP due to stretching of the 6th nerve by caudal displacement of the brain stem.” False localising sign”
  6. Bulging fontanelles in infant.
  7. Cerebral Perfusion Pressure. Q
    1. The CPP is just as important as the intracranial pressure.
  8. CPP= Mean Arterial Blood Pressure - ICP
    1. CPP 70mmHg> is generally associated with a poorer outcome.
  9. Cerebral Blood Flow.
    1. Normal: 50mL/100g of brain/minute.
    2. Below a CBF of 20 to 25 mL/100g/min, the EEG activity gradually disappears.
    3. Around 5 mL/100g/min there is cell death or irreversible brain damage.
    4. Autoregulation between 50 and 160mmHg mean pressure.
    5. Autoregulation is impaired in head injured patients

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