Frostbite with tissue necrosis

**Definition:** Frostbite with localised tissue necrosis of skin and deeper tissues

**Long definition:** Frostbite with tissue necrosis occurs following prolonged exposure of the skin to very cold temperatures. As tissue circumferentially cools to subfreezing temperatures, small extracellular ice crystals form in all skin layers, and may affect underlying soft tissue and bone. After thawing, damage to the vascular endothelial cells causes extravasation of blood with the formation of hemorrhagic blisters. In the most severe cases, distal tissue perfusion never returns after thawing and the bullae only form proximally, because tissue must be at least transiently perfused to form bullae. Tissue infarction is progressive over many weeks as microvascular thrombosis propagates proximally in the digits, with resulting delayed amputations.

**Exclusions:** - Frostbite with tissue necrosis involving multiple body regions