Published online Apr 21, 2014. doi: 10.3748/wjg.v20.i15.4160
Revised: January 22, 2014
Accepted: February 26, 2014
Published online: April 21, 2014
Radiofrequency ablation (RFA) is commonly applied for the treatment of hepatocellular carcinoma (HCC) because of the facile procedure, and the safety and effectiveness for the treatment of this type of tumor. On the other hand, it is believed that HCC cells should spread predominantly through the blood flow of the portal vein, which could lead to the formation of intrahepatic micrometastases. Therefore, monitoring tumor response after the treatment is quite important and accurate assessment of treatment response is critical to obtain the most favorable outcome after the RFA. Indeed, several reports suggested that even small HCCs of ≤ 3 cm in diameter might carry intrahepatic micrometastases and/or microvascular invasion. From this point of view, for preventing local recurrences, RFA should be performed ablating a main tumor as well as its surrounding non-tumorous liver tissue where micrometastases and microvascular invasion might exist. Recent advancement of imaging modalities such as contrast-enhanced ultrasonic, computed tomography, and magnetic resonance imaging are playing an important role on assessing the therapeutic effects of RFA. The local recurrence rate tends to be low in HCC patients who were proven to have adequate ablation margin after RFA; namely, not only disappearance of vascular enhancement of main tumor, but also an adequate ablation margin. Therefore, contrast enhancement gives important findings for the diagnosis of recurrent HCCs on each imaging. However, hyperemia of non-tumorous liver surrounding the ablated lesion, which could be attributed to an inflammation after RFA, may well obscure the findings of local recurrence of HCCs after RFA. Therefore, we need to carefully address to these imaging findings given the fact that diagnostic difficulties of local recurrence of HCC. Here, we give an overview of the current status of the imaging assessment of HCC response to RFA.
Core tip: Radiofrequency ablation (RFA) therapy is needed to ablate wider range of region than targeted tumor, including surrounding liver tissues that involve micrometastases and microvascular invasion. The local recurrence rate tends to be lower in hepatocellular carcinoma patients with an adequate ablation margin, and thus, it is essential to assess safety margin accurately to reduce local recurrence. From this point of view, we need to focus on the achievement of a sufficient ablation margin as well the lack of tumor vascular enhancement for the assessment of successful RFA. However, inflammatory hyperemia due to RFA which often appears as peripheral rim enhancement, and non-typical imaging features of tumor recurrence sometimes lead to the inappropriate diagnosis.