Cerebral edema (is an increase in brain volume due to increased fluid in the brain parenchyma or abnormal accumulation of fluid in brain tissue, which can lead to increased intracranial pressure when it exceeds the physiological regulatory limit. Intracranial hypertension affects cerebral blood circulation and metabolism, which in turn aggravates cerebral edema, and the two are mutually causal, resulting in a vicious circle. Brain edema is not an independent disease, but a non-specific response of brain tissue to various injurious stimuli, related to blood-brain barrier permeability disorders, and is the main cause of intracranial hypertension.
According to the pathogenesis, cerebral edema is clinically classified into 5 categories. The etiology and pathogenesis are as follows.
1. Vascular-derived cerebral edema
Characterized by extracellular space and white matter edema, it is the most common clinically.
(1) Etiology: craniocerebral injury, hypoxia, ischemia, and malignancy.
(2) Pathogenesis: lesions cause hydrostatic pressure of circulating fluid > tissue interstitial fluid pressure and extracellular edema caused by water extravasation. Blood-brain barrier dysfunction and increased capillary permeability of brain tissue lead to extravasation of plasma components with water into the extracellular space. A variety of transmitters such as catecholamines, epinephrine and 5-hydroxytryptamine play a key role in this.
2. Cytotoxic cerebral edema
Characterized by intracellular edema.
(1) Etiology: brain ischemia, hypoxia and poisoning and other pump energy ATP depletion.
(2) Pathogenesis: impaired energy metabolism in brain tissue, acidosis and free radical reactions, resulting in impaired cell membrane structure, dysfunctional transport and increased permeability, and massive accumulation of water in the cells. In cytotoxic edema, all brain neurons, glial cells and vascular endothelial cells are swollen and the extracellular tissue gap becomes smaller.
3.Interstitial edema
Characterized by interstitial cerebral extracellular edema or hydrocephalic cerebral edema.
(1) Etiology: brain ischemia, hypoxia and poisoning and other pump energy ATP depletion.
(2) Pathogenesis: In hydrocephalus, the ventricular canalicular membrane structure is altered, permeability increases, and cerebrospinal fluid cannot be reabsorbed through the arachnoid granules and overflows through the ventricles into the periaqueductal white matter, causing interstitial extracellular cerebral edema. Clinically, it is seen in all kinds of traffic and non-traffic cerebral edema.
4.Osmogenic cerebral edema
Characterized by the accumulation of edema fluid mainly in the glial cells.
(1) Etiology: Commonly seen in acute water intoxication, inappropriate antidiuretic hormone secretion syndrome, etc.
(2) Pathogenesis: When the osmolarity of extracellular fluid decreases water enters the cells due to osmotic pressure difference, both gray matter and white matter are edematous, and white matter is obvious.
5.Mixed edema
A variety of types of cerebral edema can coexist in the advanced stage of encephalopathy, cardiac and renal insufficiency, and systemic edema caused by malnutrition.