Surgical resection represents the gold standard for the management of LM [10]. Unfortunately, only 10–25 % of patients are amenable to liver resection due to the characteristics of either hepatic lesions (location, number, remnant liver volume) or patients (comorbidities, chemotherapic toxicity, performance status) [11]. The rationale for choosing RFA versus surgical resection in patients with LM has been multifactorial. A large percentage of patients were thought to have disease that was technically unresectable. Most of the remaining patients were poor surgical candidates for a combination of reasons, including clinically important medical comorbidities, advanced age, and aggressive disease. In this setting of unresectable patients, RFA could represent an acceptable indication [12]. The number of lesions should not be considered an absolute contraindication to RFA: nevertheless, most centers preferentially treat patients with five or fewer lesions. The target tumor should not exceed 3 cm in longest axis to achieve best rates of complete ablation with most of the currently available devices.

A particular scenario is if a colorectal cancer patient undergoes laparoscopic surgery for primary disease with synchronous LM. LRFA may be safely used concomitantly with colon resection in patients who may have resectable LM, but liver resection in a synchronous manner would be risky or, if the patient has an unresectable LM; in this case, LRFA could represent the first stage in a two-stage treatment (Fig. 13.6).

Both radiofrequency and microwave technology are effective. In RFA, high-frequency alternating current causes thermal coagulation and protein denaturation; as the temperature is increased above 45 °C, cellular proteins denature and cell structure is lost. RF ablation can be performed by either monopolar or bipolar techniques; monopolar techniques are more commonly used for tumor ablation [13]. When a monopolar technique is used, a large dispersive electrode (grounding pad) is usually placed on the patient’s thigh. Current passing through tissue from the active electrode leads to ion agitation, which is converted by means of friction into heat. The process of cellular heating induces almost immediate and irrepairable cellular damage, which leads to coagulation necrosis. The nature of the thermal damage caused by RF heating depends on both the tissue temperature achieved and the duration of heating. The diameter of coagulation necrosis was also found to be influenced by electrode diameter [14]. Currently, two RF technologies are commercially marketed (Fig. 13.7): one of these devices consists of a needle with a movable hub that deploys a variable number of curved electrodes into the adjacent tissue in a radial manner. The configurations of the multiple electrodes are designed to produce large spherical thermal injuries. The second device consists of a straight, internally cooled needle electrode. The internal cooling is designed to prevent charring of the adjacent tissues and thus any larger thermal injury. In our experience, for the particular indications in the laparoscopic approach, the “cooled” needle is preferred [4]. The major factor limiting the size of the thermal injury produced by all two devices is hepatic perfusion. Normal blood flow through the liver produces perfusion-mediated tissue cooling, above all if the lesion is near to a larger vessel (heat sink effect) [15].

MWA is another local ablation therapy, which has been used for more than 20 years [16]. It has recently attracted considerable attention because of the tremendous progress in microwave technology [17]. Microwaves generate heat by oscillation of dipole water molecules within tissues. Frequencies of 915 MHz and 2.45 GHz are currently used for tissue ablation, with a single, dual, or triple antenna (Fig. 13.8). The advantage of MWA is that the heating is primarily active, and the transmission of microwaves in living tissue is not limited by tissue desiccation and charring. In addition, MWA does not require use of earth plates on the patient’s body, thus avoiding potential earth plate burn injury that can occur with RFA. With a single application of a 2.45 GHz system, it can create a 4 × 6 cm ablation in 4 min and a 5 × 7 cm ablation in 8 min. MWs offer all of the same benefits as RFA energy for thermal ablation but they are not as dependent on tissue properties and have the ability to heat faster in a larger volume. Thus, MWs are less susceptible to perfusion or heat sinks and may be able to penetrate deeper into low-conductivity materials [18]. On the other hand, the MW antenna usually has a larger diameter (14 G) and the lack of heat sink effect increases the risk of vascular and biliary injuries. So, it’s impossible to establish which tool is better: it’s recommended to have the possibility to choose which technology depending on size and location of the tumor.