The relationship between intracranial volumes and intracranial pressures (ICP). The figure shows the different compartments within the skull, and what happens to them and the ICP (broken line) when a new pathological compartment appears. As volume increases inside the skull compensation may occur up to a certain limit by decreasing cerebrospinal fluid (CSF) and venous blood inside it. A neck collar may obstruct venous outflow, hampering this mechanism and causing a move to the right on the ICP curve. How much ICP will increase will depend on where on the pressure curve the patient is positioned.