The principles of microwave ablation are similar to those described for RFA. Microwaves cause a high frequency rotation (about 2500 MHz) in the water molecules contained in the tissue, causing it to overheat. Microwaves are emitted through the end of an electrode inserted into the tumour under ultrasound monitoring. This procedure may be performed with a percutaneous or laparotomic approach. A single application lasts about 60 s and produces an elliptical necrosis of about 2 cm around the end of the electrode. For the ablation of masses of larger size, multiple applications are necessary. Indications for microwave ablation are similar to the ones of other thermo-ablation techniques, but its effectiveness is limited to lesions larger than 2 cm. The results in treatment of metastases are still under evaluation, although they seem similar to other thermo-ablation techniques. The complete necrosis of lesions is achieved in about 50-60% of patients and the complication rates are similar to those for RFA.
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