"The term is frequently used in clinical practice to denote the combination of true cytotoxic oedema and ionic cerebral oedema. As the pathophysiology of these two types of oedema is different, as is their imaging, they are discussed separately. The remainder of this article is concerned with true cytotoxic oedema, also known as cellular oedema 8."
"Cytotoxic oedema is the result of cells being unable to maintain ATP-dependent sodium/potassium (Na+/K+) membrane pumps which are responsible for high extracellular and low intracellular Na+ concentration 6. When energy fails, as is the case in cerebral ischaemia, these pumps cease to operate and Na+ accumulates within the cell, drawing with it chloride (Cl-) and water along an osmotic gradient. This, in turn, results in cellular swelling and a reduction in the extracellular volume 9. These are the primary reasons for increased restricted diffusion on MRI."