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Background
There has been increasing use of image-guided radiofrequency (RF) ablation in the past decade to treat nonresectable hepatic tumors. Therefore, physicians performing RF ablation of hepatic malignancies should have knowledge of major complications that could stem from such procedure, which ultimately enables the operator to minimize post-ablation complications as well as exclude high-risk patients during pre-ablation assessment. The most common complications were hepatic abscess (0.66%), peritoneal hemorrhage (0.46%), biloma (0.20%), ground pad burn (0.20%), pneumothorax (0.20%), and vasovagal reflex (0.13%). Other complications were biliary stricture, diaphragmatic injury, gastric ulcer, hemothorax, hepatic failure, hepatic infarction, renal infarction, sepsis, and transient ischemic attack.

Educational Goals / Teaching Points
Identify risk factors contributing to complications following RF ablation of hepatic tumors. Identify the key imaging features of major complications following RF ablation of hepatic tumors. Discuss the importance of early detection and proper management of major complications after RF ablation of hepatic tumors.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
CT features of an abscess in the ablation zone are similar to those of a hepatic abscess. They usually appear as low-attenuation lesions with peripherally enhancing rim. Expansion of the RF ablation zone at follow-up CT also may be a sign of a hepatic abscess, especially if the patient has clinical symptoms, such as persistent fevers. CT features of a biloma in the RF ablation zone appears as a fluid collection with surrounding necrotic tissue. Bilomas caused by bile leakage from injured ducts in the ablation zone usually resolve within 4 months and, in most cases, have no clinical significance. Symptomatic bilomas may be treated with percutaneous drainage. Bleeding is another important complication that occurred during and immediately after ablation, especially coagulopathy in cirrhotic patients. Therefore, screening for coagulopathy should be performed before the procedure because needle electrodes of large diameter (17–14 gauge) are used. Efforts should be made to make sure coagulopathy is corrected before procedure to avoid bleeding. The bleeding may develop from direct mechanical injury to the vascular structure by the RF needle electrode rather than from RF thermal injury to the vessel. Given this, real-time monitoring of the whole procedure including positioning of the needle electrode is essential. Bowel injury, relatively fixed colon seems to be at more risk for perforation than the stomach or small intestine. RF ablation of a subcapsular mass within 1 cm of the adjacent bowel loops should be carefully performed and followed up closely. If a hepatic mass is close to the bowel loops, oral intake should be suspended until no bowel injury is identified at immediate follow-up CT.

Conclusion
Interventional radiologists should be aware of major RF ablation complications which begins of proper pre-ablation screening, attention to subcapsular mass in close proximity to bowel loops, and knowledge and early detection of complications on follow-up imaging.