Increased Intracranial Pressure ll: Pathophysiology

Increased intracranial pressure (ICP) refers to a potentially life-threatening rise in pressure inside the skull. This usually happens when there is a major change in the volume of brain tissue, blood, or cerebrospinal fluid (CSF) — the three components inside the skull. According to the Monro-Kellie doctrine, if the volume of one component increases, the volumes of the other components must decrease to maintain normal pressure. If this does not happen, ICP rises.

The process often begins with cerebral edema, which is the buildup of excess fluid inside or around brain cells. This swelling commonly occurs after a head injury, oxygen deprivation, stroke, or infection.

As edema develops, the brain’s ability to autoregulate its blood flow — that is, to maintain a stable blood supply despite changes in blood pressure — becomes impaired.

Once autoregulation fails, even a small increase in systemic blood pressure can push too much blood into the brain’s circulation. This further increases intracranial volume, raising ICP and worsening swelling.

Because the skull and dura mater are rigid and cannot expand, the rising pressure forces brain tissue to shift toward areas of lower resistance. This displacement is known as brain herniation.

Herniation can compress vital areas of the brainstem, affecting essential life functions such as breathing, heart rate, and consciousness. At the same time, the high pressure restricts cerebral blood flow, causing severe ischemia (a lack of oxygen to the brain tissue).

If ICP is not reduced, these changes lead to irreversible damage — including widespread neuronal death and the destruction of critical neural pathways — which can result in permanent brain injury or death.