Percutaneous ablative procedures

Percutaneous ablative techniques include both thermal and non-thermal approaches. Thermal approaches include heat-based procedure (radiofrequency and microwave ablation) and cold-based procedures (cryoablation). Thermal ablative techniques have been shown to be effective in the local treatment of tumors and are associated with a low recurrence rate. Irreversible electroporation is currently the only non-thermal ablative approach. These are described in more detail below.

• Radiofrequency ablation (RFA) – is a minimally invasive procedure that uses electrical energy and heat to destroy cancer cells. A needle is inserted through the skin into the cancer tissue and the heat produces coagulation necrosis and subsequent cell death. While RFA is a simple, repeatable, standardized, lower risk procedure, it is limited by only having a small area of effectiveness since electrical impedance develops as the tissue boils and becomes charred.⁴ This insulates the tissue from the electrical signal and results in an effective area of only few millimeters. The effectiveness of RFA is also reduced when used near large blood vessels since this results in a heat sink effect where the heat is dissipated by the blood flowing through these vessels. Besides tumor location, other factors which impact the effectiveness of RFA include the size and number of tumors and the need for a large tumor-free margin.
• Microwave ablation – Microwave ablation uses high frequency microwave energy to heat and kill cancer cells. A thin probe containing an antenna which emits microwaves is into the tumor. The probe produces intense heat that destroys tumor tissue via coagulation necrosis, often within 10 minutes. Microwave ablation has a number of advantages over RFA including faster heating over a larger area, shorter procedure time, no need for a grounding pad, resistance to the heat sink effect, and less pain.
• Cryoablation –  Cryoablation causes rapid cooling of the target tissue, resulting in intracellular ice crystal formation that destroys organelle and cell membranes and induces membrane pore formation that disrupts the electrochemical gradient. Cellular tonicity is also disturbed, causing lethal transmembrane fluid shifts. If these changes do not cause immediate cell death, they often initiate apoptosis. The ability to visualize ice ball formation, the edge of which marks the 0°C isotherm, in cryoablation on several imaging modalities is a particular benefit.
• Irreversible electroporation (IRE) therapy – IRE is a nonthermal ablation technique that induces cell death by disrupting the electric potential gradient across cell membranes, leading to the formation of permanent nanopores through the plasma membrane, altering cellular transport and ultimately cell homeostasis.⁵ The procedure involves the delivery of a series of high voltage direct current electrical pulses between two electrodes placed within a target area surrounding the tumor. Since IRE is a nonthermal treatment, it has the advantage over thermal ablative treatments since the treatment zone can cross large blood vessels and bile ducts without damaging these vital structures.