4 - Increased Intracranial Pressure

Abstract

Intracranial hypertension (IH) is a clinical condition that is associated with an elevation of the pressures within the cranium. The pressure in the cranial vault is measured in millimeters of mercury (mm Hg) and is normally less than 20 mm Hg.The cranium is a rigid structure that contains three main components: brain, cerebrospinal fluid, and blood. Any increase in the volume of its contents will increase the pressure within the cranial vault. The Monroe-Kellie Doctrine states that the contents of the cranium are in a state of constant volume. That is, the total volumes of the brain tissues, cerebrospinal fluid (CSF), and intracranial blood are fixed. An increase in the volume of one component will result in a decrease of volume in one or two of the other components. The clinical implication of the change in volume of the component is a decrease in cerebral blood flow or herniation of the brain.CSF is a clear fluid found in the subarachnoid spaces and ventricles that cushions the brain and spinal cord. It is secreted by the choroid plexus in the lateral ventricles, travels to the third ventricle via the foramen of Monroe. From the third ventricle, CSF reaches the fourth ventricle through the aqueduct of Sylvius. From here, it flows into the subarachnoid space via the foramina of Magendie and Luschka and is eventually reabsorbed into the dural venous sinuses by arachnoid granulation.