Cryogenic freezing of tissue cells can lead to cellular damage and vascular injury, physical, chemical, and electrolyte changes in tissue cells and their contents, and finally to cellular necrosis or apoptosis. Cryotherapy consists of two processes: freezing and rewarming. The formation of extracellular ice crystals at the initial stage of freezing (-4~-21℃), i.e., the “solution effect” (solution
effect) is the main mechanism that causes cell death. The formation of extracellular ice crystals increases the extracellular osmotic pressure, causing intracellular dehydration, resulting in cellular crumpling, which in turn causes damage to cell membranes and organelles. A further decrease in temperature can cause the formation of intracellular ice crystals, leading to irreversible damage to organelles, followed by damage to cell membranes, and eventually cell death. Small ice crystals recrystallize or fuse with each other to form large ice crystals during rewarming, and the large ice crystals have a stronger destructive effect on cells. In addition, the melting of cellular ice crystals during rewarming makes the extracellular space a hypotonic environment, and water enters the cells, causing cell swelling and leading to cell membrane destruction, thus allowing some cells that were not damaged during the freezing period to be destroyed during the rewarming process. Vascular injury mainly occurs during the rewarming period of freezing, and is a delayed injury. It is characterized by microvascular disruption, microthrombus formation, blood flow stagnation and occlusion, and tissue cell hypoxia leading to cell necrosis. Some studies have pointed out that although micro and small arteries and veins are still difficult to recover within 4 hours after rewarming, large vessels, especially large arteries, are generally not damaged, and even if damaged, they can generally recover within the following 24 hours, which has practical implications in clinical practice and allows tumors adjacent to large vessels to be safely treated by cryotherapy.