Many acute brain injuries are associated with the development of oedema within the cerebral parenchyma. The resulting expansion of brain volume can cause an increase in intracranial pressure (ICP). This phenomena is explained by the Monro-Kellie doctrine. A pressure-volume relationship, it states how within the fixed compartment of the skull the volume of the non-compressible contents (brain, CSF and blood) will stay constant within a dynamic equilibrium. An increase in one component will lead to reciprocal decrease in the others. Largely this compensation is from the displacement of low-pressure venous blood. Once these mechanisms are exhausted, a precipitous rise in ICP will follow. Left untreated, cerebral perfusion pressure will become compromised and risks brain herniation.
It is worth noting that younger individuals are at a greater risk of catastrophic rises in intracranial pressure due to a larger baseline brain volume.
