Healing responses following cryothermic and hyperthermic tissue ablation

Minimally invasive, thermally ablative, interventional technologies have been changing the practice of medicine since before the turn of the 20th century. More recently, cryothermic and hyperthermic therapies have expanded in terms of their spectrum of thermal generators, modes for controlling and monitoring the treatment zone and both benign and malignant medical applications. The final tissue, and hence clinical outcome, of a thermal ablation is determined by the summation of direct primary (thermal) and secondary (apoptosis, ischemia, free radical, inflammation, wound healing, etc.) injury followed by possible cellular regeneration and scar formation. The initial thermal lesion can be broadly divided into two major zones of cellular death: 1) the complete ablation zone closer to the thermal source and 2) the peripheral transition zone with a decreasing gradient of cell death. While not applicable to cryotherapy, hyperthermic complete ablation zones are subdivided into two zones: 1) thermal or heat fixation and 2) coagulative necrosis. It is important to clearly differentiate these tissue zones because of their substantially different healing responses. Therefore, the development of clinically successful thermal therapies requires an understanding of tissue healing responses. The healing responses can be affected by a number of additional factors such as the tissue's anatomy, organ specific healing differences, blood supply, protein vs. lipid content, and other factors. Thus, effective biomedical instrument development requires both an understanding of thermal cell injury/death and the body's subsequent healing responses. This paper provides a general overview of the healing pathways that follow thermal tissue treatment.