Hepatic microwave ablation: a review of the histological changes following thermal damage

Abstract

Microwave (MW) ablation therapy is a local treatment by which tumours are destroyed by coagulation from the passage of MWs into cells. The aim of this review is to examine histological results obtained from preclinical and clinical studies. A literature search was undertaken for all studies focusing on MW therapy and in which lesions were excised for a complete histopathological examination after treatment. Two main zones were described after ablative therapy (central and transitional Microwave (MW) coagulation therapy is a form of local ablation where tumours are destroyed by thermal coagulation that develops from the passage of MWs into cells and the production of frictional movement between molecules (1). Initially developed in the early 1980s to achieve haemostasis along the plane of transection during hepatic resections (2), MW coagulation of tissue surfaces proved slower than electrocautery units and produced deeper areas of tissue necrosis. These two characteristics, while making MW unsuitable for operative haemostasis, are potentially useful in the ablation of liver tumours. Like radiofrequency (RF) ablation and laser-induced interstitial thermotherapy, MW is very versatile and can be performed percutaneously using ultrasound or computed tomography (CT) guidance, or at laparoscopy or laparotomy with intra-operative ultrasound guidance.The formation of the thermal lesion during the ablation process is a complex combination of MW energy absorption, heating conduction and possible tissue water evaporation, condensation and movement. In 2002, Izzo (3) suggested that the production of very small zones of coagulative necrosis by the intratumoral MW-emitting needle electrodes would require frequent repositioning at 5-10 mm intervals to create multiple overlapping zones of coagulative necrosis. He also suggested that MW should not be performed near major bile ducts and blood vessels because of the description of vascular and biliary complications in these locations. However, since the appearance of that review, numerous technical advances have been introduced in MW engineering and subsequently evaluated histologically in a number of preclinical and clinical studies.The aim of this review is to examine those studies and determine the factors that influence the production of an area of ablation and the evidence for its use under different circumstances. Materials and methodsA literature search was undertaken for all studies focusing on MW ablative therapy where lesions were excised for a complete histopathological examination after the treatment.Articles were selected from the MEDLINE, EMBASE and Cochrane Library databases, using the key words microwave, ablation or ablative therapy, liver, hepatic, in vivo, ex vivo, clinical, experimental. Only articles published in the English literature were used. We

Laparoscopic microwave thermosphere ablation of malignant liver tumors: an initial clinical evaluation

“…Since charring and desiccation do not occur, larger ablation zones in a shorter time compared to RFA are possible [3][4][5][6][7][8]. Nevertheless, the early microwave systems have suffered from large antenna diameters, antenna shaft heating, small ablation zones created due to low power outputs and concerns for thermal injuries [9,10]. A significant criticism for MWA was that spherical ablation zones were not possible with a single antenna.…”

Effect of Change in Portal Venous Blood Flow Rates on the Performance of a 2.45-GHz Microwave Ablation Device

“…The consensus from those experiments is that blood vessels larger than 3-4 mm adjacent to or embedded within ablation zones cause substantial local "heat sink effect" on radiofrequency ablation zones but little to no effect on microwave ablation zones created by using either 915-MHz or 2.45-GHz devices (14)(15)(16)(17)(18)(19)(20)(21). Also, temporary occlusion of regional or global hepatic blood flow causes an increase in the overall size of ablation zones created by radiofrequency and microwave ablation devices (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)13,17,22,23). The studies of the change in hepatic blood flow within the normal physiological range have demonstrated as much as a threefold decrease in radiofrequency ablation zone volume as hepatic blood flow reaches upper physiological rates (11,25) but little to no effect of physiological fluctuations in hepatic blood flow on ablation zone volume created by 915-MHz microwave ablation devices (25).…”

Emerging Trends in Oncology: Greater Role for Radiology

“…The heat sink effect is also less in microwave when compared to radiofrequency ablation [8]. The ablation zones created by microwaves have been found to reach up to 7 cm [9][10][11], creating the opportunity to treat larger tumours percutaneously. Another advantage is shorter ablation times [12].…”