This represents the summation of the volumes of the brain (1200-1600 ml), blood (100-150 ml) and CSF (100-150 ml). It increases exponentially in the presence of an expanding intracranial mass lesion once a critical point is reached when compensatory mechanisms are overwhelmed. Compensation can be achieved by a reduction in intracranial blood volume, displacement of CSF into the spinal subarachnoid space and by increased absorption of CSF. Rapid development of a mass lesion is associated with earlier decompensation.
The elastance of the cranio-spinal axis is determined by the rigidity of the skull; the elasticity of the intracranial and spinal dura; and displacement of the mobile neuraxis contents, blood and CSF, within the cranio-spinal axis.
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