In immunology, leukocyte extravasation (also commonly known as leukocyte adhesion cascade or diapedesis – the passage of cells through the intact vessel wall) is the movement of leukocytes (white blood cells) out of the circulatory system (extravasation) and towards the site of tissue damage or infection.

Escape of blood from vessels.

Fluid leakage causing localized swelling.

Leakage of fluid into tissues.

Cyst from ruptured salivary gland.

Extravasation of urine refers to the condition where an interruption of the urethra leads to a collection of urine in other cavities (extravasation), such as the scrotum or the penis in males.