Microwave tissue coagulation has been applied to achieve hemostasis along incision in an effort to reduce blood loss during hepatic resection, particularly for high-risk patients with HCC and cirrhosis. Microwave tumor coagulation has been performed intraoperatively and during laparoscopy, most frequently as an alternative to hepatectomy in patients with unresectable HCC. This technique has been associated with excellent initial success, and offers the potential for cure, favorable survival rates, a low rate of local recurrence, low operative morbidity and mortality, and the option of repeat therapy. Similar application of microwave coagulation therapy has been performed less extensively for liver metastases.

 

PRINCIPLES

Similar to the radiofrequency ablation, tissue necrosis induced by percutaneous microwave tissue coagulation (PMCT) is the consequence of the conversion of energy to heat, with secondary coagulation necrosis. Water molecules polarize with the electromagnetic radiation of the microwave. The 2450 MHz microwave provides a rapidly alternating electromagnetic field. As the water molecules follow the changing polarity of the field, heat is generated from within the tissue, resulting in coagulation necrosis and hemostasis. Tissue coagulation occurs in a spindle-shaped configuration around the monopolar lead. Tissue deep to the tip or beyond the few centimeters of penetration around the shaft of the electrode is not affected.

 

INDICATIONS

Microwave tissue coagulation has recently been applied percutaneously for therapy of unresectable primary HCC and hepatic metastases, offering an alternative to other percutaneous interstitial technique of liver tumor ablation.

 

PROCEDURES

PMCT is performed under continuous ultrasound guidance with local anesthesia. The microwave electrode is positioned in the tumor under ultrasound guidance and microwaves are administrated at 60W for 60-120 sec at one or more locations in the lesion depending on lesion size. Stepwise microwave emissions at 60 W for 10 sec have been applied during electrode withdrawal to achieve hemostasis and avert bile leak and tumor seeding. More than one session may be necessary depending upon lesion size and number. During real-time ultrasound monitoring, the lesion become hyperechoic immediately following microwave application.

 

ADVERSE EFFECTS

PMCT has resulted in no reported serious complications. The most common adverse effects are mild pain lasting a few hours and fever of 37-38°C lasting a few days. Treatment of a superficial lesions may induce ascites and pleural effusion with no specific management.

 

FOLLOW-UP

Follow-up includes imaging, serum tumor marker assay, and selective use of biopsy. The imaging finding of microwave-induced necrosis are indistinguishable from those of tissue necrosis achieved with other percutaneous tumor ablative procedures. Loss of enhancement at CT and signal loss on T2-weighted MRI image are indicative of tumor necrosis.