Increased Intracranial Pressure

Excerpt

Intracranial hypertension refers to a clinical condition characterized by elevated pressure within the cranial vault. Normal intracranial pressure (ICP) in adults typically ranges from 7 to 15 mm Hg in the supine position. Values above 20 to 25 mm Hg are generally considered pathological and may warrant intervention.

The cranium, a rigid and nonexpandable structure, houses 3 primary components: brain tissue, cerebrospinal fluid (CSF), and blood. Any increase in the volume of one of these components leads to a rise in ICP. According to the Monro-Kellie doctrine, the total volume within the cranium remains constant. A volume increase in one component necessitates a compensatory decrease in one or both of the others. Clinically, such volume shifts can reduce cerebral blood flow or precipitate brain herniation. Failure of compensation leads to increased ICP, which can reduce cerebral perfusion pressure (CPP) and ultimately cause ischemia or herniation.

CSF, a clear liquid located within the subarachnoid space and brain ventricles, serves to cushion the brain and spinal cord. The choroid plexus in the lateral ventricles produces CSF, which then flows through the foramen of Monro into the third ventricle. From there, it passes through the cerebral aqueduct (aqueduct of Sylvius) into the fourth ventricle. CSF exits the fourth ventricle via the foramina of Magendie and Luschka, enters the subarachnoid space, and ultimately is reabsorbed into the superior sagittal sinus and other dural venous sinuses via arachnoid granulations.