Intracranial Hypertension & Herniation

The understanding of intracranial pressures (ICP), requires a foundational knowledge of the Monro-Kellie Doctrine / Hypothesis, which describes the relationship between the volume of the cranial vault and ICP as the following: 

1. The sum of the volume of brain, csf and blood is constant

2. The increase in one component must be compensated for by a proportional decrease in the others

When compensatory mechanisms are exhausted, and elevated ICP results. 

Components of the Cranial Vault:

1. Brain (approx 80%)

2. Venous and arterial blood (each 5%)

3. CSF (10%) 

In general, the volume of intracranial contents can increase up to 10%, but this percentage depends on the volume of the brain parenchyma and its ability or inability to accept changes in volume—a higher percentage may be tolerated in an older brain with atrophy than in a younger brain.  

Once compensatory mechanisms fail...