Image guided percutaneous tumor ablation has gained high acceptance in the treatment of malignant liver lesions when surgical options are precluded (7
). Consequently, according to the Barcelona Clinic Liver Cancer, staging classification and treatment schedule for percutaneous ablation is recommended in patients with early-stage hepatocellular carcinoma, if patients are excluded from surgical options (11
). Among the different ablation techniques, thermal ablation with radiofrequency is the most widespread technique and has been shown to be associated with higher efficiency and greater survival benefit compared to the non-thermal PEI (8
). However, centrally located or subcapsular lesions close to the gallbladder, stomach, bowel or heart still pose a challenge for percutaneous thermal ablation techniques in the liver. Due to the spread of heat to the adjacent structures, there is a risk of thermal damage. Several methods have been proposed to overcome the heat mediated destruction of adjacent structures, such as instillation of air, CO2
or 5% dextrose water (9
). Nevertheless, there are still locations, e.g., subcapsular lesions close to the heart, where thermal protection of the adjacent structures is not possible. The ablation of centrally located liver lesions is hindered by the heatsink effect as well as the risk of damage to the central bile ducts (13
). Thus, there are still circumstances where a percutaneous ablation of malignant liver lesions is either risky or cannot be performed at all.
Irreversible electroporation, as new non-thermal ablation technique of soft tissue, offers the possibility to overcome the aforementioned limitations of thermal ablations. Two or more monopolar probes or a single bipolar probe must be used at a time. The number of monopolar probes that are used during an IRE procedure depends on the size and shape of the desired zone of tissue ablation. The system can be used with up to six single electrode probes at a time. The treatment parameter for voltage depends on the distance between the probes within the targeted tissue. IRE uses a series of electrical pulses for microseconds in order to generate irreversible permeabilization of cell membranes, and thereby induces apoptosis in the treated tissue. IRE proved to be highly effective in tissues with high density of cell wall structures and less effective in tissues with high concentration of collagenous and elastic fibers (4
). As a non-thermal technique, IRE is not limited by the heatsink effect. There appears to be complete ablation up to the margin of blood vessels without compromising to the functionality of the blood vessels (6
). This - in contrast to thermal ablation - allows tumor cell ablation without concomitant destruction of the connective tissue, bile ducts, blood vessels and nerves, which implies the ablation of tumor cells also in those areas where thermal ablation was not possible before.
Irreversible electroporation proved to be a promising treatment option in patients with inoperable HCC. In central tumor lesions close to the liver hilum or lesions close to larger blood vessels and bile ducts, conventional RFA cannot be performed. Furthermore, subcapsular lesions and those in the vicinity of other organs (i.e., heart, gallbladder, stomach and bowel) are not treatable with conventional RFA. Due to its selective and non-thermic ablation and the obvious decrease of limitations and contraindications, IRE widens the field of minimally invasively treatable lesions.
As a first step, we demonstrated in our case that a tissue around a TIPS stent-graft can be fully ablated by IRE with complete preservation of the stent-graft and the TIPS flow. We also found no impairment of bile flow even though a large centrally located tissue volume was ablated. For further evaluation of the IRE ablation technique regarding the extent of ablation, the procedure's side effects and patients' outcome as well as the potential overall-survival benefits, prospective studies will have to be performed.