Intracranial mass effect
This includes conditions like brain tumors, hematomas, abscesses, and cerebral edema. These space-occupying lesions increase the volume within the cranial vault and can compress surrounding brain structures, impeding venous outflow and worsening intracranial hypertension.
Impaired cerebrospinal fluid dynamics
Conditions such as hydrocephalus or infections like meningitis and encephalitis can impair CSF absorption or circulation, leading to CSF accumulation and increased ICP.
Cerebral blood volume changes
Both hyperemia and venous outflow obstruction can contribute to increased ICP. For example, hypercapnia (increased PaCO2) causes cerebral vasodilation, thereby increasing cerebral blood volume and ICP. Additionally, conditions like traumatic brain injury (TBI) can disrupt the blood-brain barrier, resulting in vasogenic edema that further elevates ICP.
Cerebral edema
This refers to an abnormal accumulation of fluid within brain tissue. There are two main types of cerebral edema: cytotoxic and vasogenic. Cytotoxic edema results from cellular injury and swelling, often seen in ischemic stroke or trauma. Vasogenic edema is due to increased permeability of the blood-brain barrier, as seen in brain tumors and infections.
When these compensatory mechanisms become overwhelmed, intracranial hypertension results. Increased ICP reduces cerebral perfusion pressure (CPP), which is calculated as the mean arterial pressure (MAP) minus the ICP. A decrease in CPP can lead to ischemia and impaired neuronal function, ultimately progressing to irreversible brain damage if untreated.
| Mechanism | Examples | How it raises ICP |
|---|---|---|
| Intracranial mass effect | Brain tumors, hematomas, abscesses, cerebral edema | Space-occupying lesions increase the volume within the cranial vault, compress surrounding brain structures, and impede venous outflow |
| Impaired CSF dynamics | Hydrocephalus; infections such as meningitis and encephalitis | CSF absorption or circulation is impaired, so CSF accumulates |
| Cerebral blood volume changes | Hyperemia; venous outflow obstruction; hypercapnia | Raised PaCO2 causes cerebral vasodilation, increasing cerebral blood volume |
| Cytotoxic edema | Ischemic stroke, trauma | Cellular injury and swelling accumulate fluid within brain tissue |
| Vasogenic edema | Brain tumors, infections; traumatic brain injury disrupting the blood-brain barrier | Increased blood-brain barrier permeability lets fluid pass into brain tissue |