10 or 15 or 20 or 40 mmHg? What is Increased Intracranial Pressure and Who Said So?

Increased intracranial pressure (ICP) has been recognized since the early 1900s as an important mechanism for additional brain injury after the first impact. Increased ICPs are not always consequential; in fact, we all experience them daily. For example, coughing or straining has been shown to cause large, abrupt cerebrospinal fluid pressure fluctuations [1]; these arise out of communication between the cerebrospinal fluid and intrathoracic pressures through the venous system, but the surges are absorbed without damaging brain tissue. Head positioning (whether elevated or rotated) is also critical if the hydrodynamics are in free communication. When a new intracranial mass appears (e.g., blood clot, swollen infarcted tissue, tumor swelling), a resulting increase in ICP may cause the brain to shift, resulting in pressure necrosis in the cingulate gyrus and occipital cortices. Diffusely increased pressure most significantly impacts the parahippocampal gyri. Increased pressure in the posterior fossa, mostly from a cerebellar mass, causes the cerebellar tonsils abutting the rim of the foramen magnum to turn necrotic. …