Irreversible electroporation (IRE) is a new technology that uses very high voltage (1500 V/m²) at very low direct current (nanoamperes) passing through tissue between the positive and negative electrodes for multiple brief pulses (nanoseconds). The flow of electricity creates irreparable holes in cell membranes, inducing apoptosis. This technique does not produce heat or destroy stromal framework, so it is desirable for use near intrahepatic blood vessels and bile ducts, where significant heat generation would produce collateral damage. Normal bile duct and endothelial cells repopulate along the remaining stromal framework. We employ IRE (NanoKnife®, AngioDynamics, Latham, NY, USA) when RFA would be too close to hilar structures to avoid damage to main bile ducts, usually for tumors of 3 cm or less. Two to four electrodes are placed into or near the tumor to create an electric current field of sufficient size to ablate the tumor (Fig. 20.4a).

Ultrasound or CT guidance is used to place the 18-gauge needles (Fig. 20.4b). It is important to place the electrodes parallel to each other in multiple planes to produce the desired current flow and maintain uniform tissue impedance. Placing needles 2.5 cm apart appears to be optimum spacing (Fig. 20.4c). It is also important to place the electrodes parallel to major vascular structures so as not to traverse the lumens with the needles, which will increase the risk of postprocedure thrombosis.

Often midgut NETs metastatic to the liver are surrounded by a pseudocapsule, and these tumors are very dense. They can be enucleated (Figs. 20.5 and 20.6) by crushing the hepatic parenchyma near the tumor with a hemostat, clipping the feeding structures with fine hemoclips, and tying the larger vessels prior to division. Alternatively, an energy resective device such as the LigaSure™ (Medtronic–Covidien, Minneapolis, MA, USA) can be used. Enucleation preserves the greatest amount of normal intervening liver and is useful for multiple or single superficial tumors of the liver. It also can be done laparoscopically. Despite positive margins of resection, recurrence rates remain low using this technique.

More formal segmental or lobar resections are performed along the Couinaud resection lines (Fig. 20.7a) following the venous system. Ultrasound is used to note the location of the veins within the liver. The larger trunks are not amenable to sealing and dividing with the energy devices currently available (LigaSure™; Harmonic® scalpel, Ethicon Endo-Surgery, Cincinnati, OH; Aquamantys®, Medtronic, Minneapolis, MN), but the smaller branches entering the segments can usually be adequately sealed with these devices. The crush and clip or tie technique and/or an energy device is used to divide the hepatic parenchyma. Liver compression sutures of 2-0 chromic on a blunt needle are used as an adjunct for hemostasis along resection lines (Fig. 20.7b). Intraoperative ultrasound should be employed to map out the larger vascular structures; these can be divided with the endoscopic vascular stapler inserted directly into the hepatic parenchyma (Fig. 20.7c), or by conventional suture ligature. This technique is best applied to superficial lesions. Despite tumor cells at the margin, recurrence rates are generally low.