Minimally Invasive Techniques for the Treatment of Liver Tumors

John R. Leyendecker, M.D. and Gerald D. Dodd III, M.D.

Semin Liver Dis. 2001;21(2) 

In This Article

Microwave Ablation

An alternative means of producing thermal coagulation of tissue involves the use of microwaves to induce an ultra-high-speed (2450 MHz) alternating electric field, causing the rotation of water molecules. Although the use of microwaves for tissue ablation is not new, the majority of the clinical experience with this technique to ablate liver tumors comes from Japan. Percutaneous microwave ablation was first used as an adjunct to liver biopsy in 1986, but it has since been used for hepatic tumor ablation.[22] As with RF ablation, microwave ablation involves placement of a needle electrode directly into the target tumor, typically under US guidance. Each ablation also produces a hyperechoic region around the needle, similar to that observed with RF ablation. Unlike RF ablation, however, no retractable prongs are used, and the resulting ablation tends to be much more elliptical. For this reason, the expected diameter of ablation is less than with RF ablation and measures slightly greater than 2 cm. Therefore, more sessions may be needed to treat larger tumors. However, the treatment sessions may be shorter than for RF ablation because an ablation is produced in 60 sec with microwave therapy. Despite the differences, the indications, contraindications, and patient selection criteria for microwave ablation are similar to those presented for RF ablation.[23]

Relatively fewer results are available for microwave ablation of liver tumors than for RF ablation. In 1994 Seki et al[24] treated 18 patients with small (up to 2 cm), solitary examples of HCC using a percutaneous electrode placed under US guidance. Of these 18 patients, three developed recurrent disease distant from the site of original tumor, and 1 died of unrelated causes 22 months after treatment during follow-up of 11 to 33 months. Subsequently, Murakami et al[25] treated nine patients with HCC exceeding 3 cm in diameter who had received previous chemoembolization. Patients were followed for up to 9 months, and radiologic evidence of complete necrosis was present in five lesions. Matsukawa et al[26] reported on 24 patients with HCC or metastases who were likewise treated with microwave ablation, most after chemoembolization. Sixty percent of the HCC and 57% of the metastases appeared to be completely ablated by follow-up CT, with better results achieved in smaller tumors and well-differentiated tumors. In a larger series of 41 patients with HCC and 10 patients with hepatic metastases, Dong et al[27] performed percutaneous microwave ablation on tumors up to 8.7 cm in diameter. During a mean follow-up of 23 months, three patients with HCC died of causes unrelated to their original tumor or treatment, and three patients developed new tumor nodules. During a mean follow-up of 13 months, five patients treated for metastatic disease developed new tumor nodules, which were also treated with microwave ablation, and two patients died of their disease.

Reported complications of microwave ablation are similar to those reported for RF ablation and are typically mild, including pain, fever, liver enzyme elevation, ascites/pleural effusion, diaphragm injury, and needle track seeding.