Cryoablation and Radiofrequency Ablation

There are several other nonresectional techniques for obliterating tumors in the hepatic parenchyma. These modern ablative procedures include cryoablation and radiofrequency ablation (RFA). In both cases, a major operation is typically required, although both may be employed laparscopically and even percutaneously in select circumstances. In both cases, a probe is placed into the tumor, typically under ultrasound guidance. For RFA, microwave energy is passed down the probe into the tumor; cooking it to death. For cryoablation, liquid nitrogen is passed down the probe creating an ice ball; freezing the tumor to death. It is easier to follow the growth of the ice ball in relation to tumor margin with ultrasound than it is to follow the RFA coagulative lesion in real time, so the security of the margins may theoretically be better with cryoablation. However, RFA is more widely available. In both cryoabalation and RFA, the frozen or coagulated tissue is typically left in situ; to be gradually resorbed later. These thermal ablation techniques are more akin to nonanatomic resections in that they may be undertaken without regard for segmental anatomy.

There are limitations, however. Tumors adjacent to the major vascular channels (portal or hepatic vein or IVC) may not be reliably ablated because the blood flow acts as a thermal sink, protecting the malignant cells on the vessel wall from the applied temperature extremes. The great advantage of these techniques is that they can destroy tumor in disparate parts of the liver and preserve intervening parenchyma. They are, therefore, ideally suited to smaller tumors. Indeed, the larger the amount of dead (frozen or coagulated) left in the liver, the more likely are adverse systemic consequences. These adverse consequences are a variant of a systemic inflammatory response and include thrombocytopenia, myoglobinuria, ATN, and noncardiogenic pulmonary edema. They are increasingly prevalent as the volume of ablated tissue passes 30% of the liver volume, and appear to be more prevalent following cryoabalation than following RFA (6).

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