For a cooling rate of 25 C/min, at a temperature of about - 10 C there is a sudden decrease in cell destruction. Experiments have shown that this sudden increase in cell destruction corresponds to sudden formation of intracellular ice. Intracellular ice forms because the water transport through the cell membrane is a rate dependent process. When cells are cooled too rapidly to equilibrate in concentration with the extracellular solution, the intracellular solution becomes increasingly thermodynamically supercooled and unstable. The probability for intracellular ice formation increases with supercooling. The nucleation sites for intracellular ice formation are intracellular, or extracellular or on the membrane. Whatever the cause of intracellular ice may be, it appears that it is almost always lethal to the cell. It is possible that intracellular ice per se is lethal or the processes that led to the formation of the intracellular ice, such as damage to the cell membrane, are lethal. As with the hyperosmotic solution mechanism of damage, with intracellular damage the mesoscale phenomena are known while the nanoscale are not. In cryosurgery the mechanism of rapid cooling and intracellular ice formation occurs usually in the frozen lesion near the cryosurgical probe. It is thought that near the cryosurgical probe the cells are completely destroyed.
In cryosurgery the freezing cells are in tissue, which has a different configuration from a cellular suspension. In tissue cells are in an organized structure and the volume of the extracellular space is usually smaller than that around cells in a suspension. The few experimental results show that the process of freezing of cells in tissue and in suspension is roughly similar. In tissue ice usually forms first in the extracellular space. Ice appears to usually form in the vasculature and propagate in the general direction of temperature gradients, but in and along blood vessels. In addition it was found that in the prostate ice forms in the ducts, in the breast in the connective tissue and in the kidney in the ducts. The cells in the various tissues appear to also experience cellular dehydration and intracellular ice formation. In liver freezed dehydrated hepatocytes, surrounding expanded sinusoids. A mathematical analysis of the process of freezing in the liver compared the process of freezing of hepatocytes in the liver and in a cellular suspension. The results demonstrate that in both cases hepatocytes experience a similar dehydration process and a similar probability for intracellular ice formation. Therefore cells in tissue will probably experience both qualitatively and quantitatively similar mechanisms of hypertonic solution damage and intracellular ice formation damage like cells frozen in cellular suspensions. However, it is suggested that in tissue the dehydration o f cells will most likely result in a disruption of the vasculature and of the connective tissues.