Practical pathology perspectives for minimally invasive hyperthermic medical devices

Abstract

Currently, hyperthermic-based minimally invasive medical devices are available for the treatment of dysfunctional and neoplastic tissues in a variety of organ systems. These therapies employ a spectrum of modalities for delivering heat energy to the targeted tissue, including radiofrequency/microwave, high intensity focused ultrasound, conductive/convective sources and others. While differences in energy transfer and organ systems exist, hyperthermic treatment sites show a spectrum of changes that intimately correlate with the thermal history generated in the tissue (temperature-time dependence). As a result, these hyperthermic medical technologies can be viewed using a approach. First, the thermal applications themselves can be globally categorized along a high-dose ablation to low-dose ablation to lowdose non-ablative rejuvenating slope. Second, the resultant tissue changes can be viewed along a decreasing thermal dose gradient from thermally/heat-fixed tissue necrosis to coagulative tissue necrosis to partial tissue necrosis (transition zone) to subtle non-necrotizing tissue changes. Finally, a gradient of cellular and structural protein denaturation is present, especially within the transition zone and adjacent viable tissue region. A hyperthermic treatment's location along these gradients depends more on the overall thermal history it generates than the amount of energy it deposits into the tissue. The features of these gradients are highlighted to provide a better understanding of hyperthermic device associated tissue changes and their associated healing responses.