Pathophysiology

Cytotoxic edema is defined as the premorbid cellular process, also known as cellular edema, oncotic cell swelling, or oncosis, in which extracellular Na+ and other cations enter neurons and astrocytes and accumulate intracellularly, partly due to failure of energy-dependent extrusion mechanisms. Uncontrolled influx of cations occurs primarily through cation channels. The influx of cations in turn leads to an influx of anions, maintaining electrical neutrality, and together these phenomena drive the influx of water, resulting in osmotic expansion of the cell, that is, cytotoxic edema. Cytotoxic edema itself does not cause brain swelling, but the formation of cytotoxic edema depletes the extracellular space of Na+, Cl–, and water, thereby creating a new gradient for these molecules across the capillaries of the blood-brain barrier[^1]. The blood-brain barrier remains intact in this form of cerebral edema; therefore, there is no protein extravasation, and consequently this form of cerebral edema does not show enhancement on CT or MRI.

Etiology

This form of cerebral edema occurs, for example, in the setting of Traumatic brain injury.