Heat injury to adjacent bile ducts remains a problem because bile flow is slow and has little cooling effect in contrast to blood flow, and MWA may ablate surrounding tissue of antenna rapidly because of higher thermal efficiency [15, 19]. Excessive heating to overcome the “heat sink effect” of hilar large vessels can cause significant damage to the major bile ducts. Bile duct stricture may develop weeks to months after thermal ablation due to heat damage to the bile duct [14, 20]. Strictures of the peripheral bile ducts may not cause any symptoms, but that of the central bile ducts can cause cholestasis, biliary infection, liver abscess, or injury of liver function. Complications related to bile duct injury were reported to occur in between 0 and 25.6 % with an average of 11.7 % [21]. In Liang’s study [17], 1,136 patients with 1928 malignant liver tumors underwent ultrasonographically guided percutaneous MWA; the incidence of bile duct injury was 0.2 % (2/1,136). One patient with an HCC 10 mm away from the hepatic hilum underwent three sessions of MWA. CT depicted dilatation of the right hepatic duct owing to bile duct stenosis near the hepatic hilum 32 days after MWA; the dilatation was relieved by placing a stent. The other patient with a metastasis 7 mm away from the hepatic hilum underwent two sessions of MWA. A biloma was detected 38 days after MWA, and it was cured after 3 months of drainage. In Ren’s study [16], MWA was performed together with percutaneous ethanol injection on 18 malignant liver tumors adjacent to the hepatic hilum, and thrombosis was found in the right portal vein and the umbilical part of the left portal vein by CEUS in one patient 1 month after treatment, which disappeared 3 months later without any management, but no injury to the bile duct occurred.

In order to gain complete ablation of the tumor and avoid relative complications, there are some key points: (1) carefully consider the route of antenna insertion and the anatomical relationship between the tumor and the portal vein and main bile duct on ultrasound scrutiny; (2) to gain complete ablation of the tumor periphery adjacent to the hilum, percutaneous ethanol injection is performed simultaneously with microwave emission to augment the effect of MWA; (3) to avoid bile duct injury during ablation, long-duration, low-power (45–50 W) ablation and intermittent microwave emission should be performed, and real-time temperature monitoring during MWA may help to prevent thermal-mediated bile duct injury; and (4) MWA can be used in combination with other techniques to augment the ablation effect, such as transarterial chemoembolization (TACE), intraductal chilled saline perfusion (ICSP), and estimation of spatial location of the tumor by 3-D visual software.

Other thermal ablation techniques include radiofrequency ablation, high-intensity focused ultrasound, laser ablation, and percutaneous ethanol injection, among which radiofrequency ablation gets the most popularity in the treatment of malignant liver tumors. However, no special study is reported on the ablation effect of tumors adjacent to the hepatic hilum, so the clinical efficacy could not be determined accurately. Here, clinical efficacy and complications of ablation of malignant liver tumors in high-risk locations by these ablation techniques are summarized.