Radiofrequency Ablation of Hepatic Lesions: A Review

Venkataramu N. Krishnamurthy, MD; V. Javier Casillas, MD; Lina Latorre, MD

Disclosures

Appl Radiol. 2003;32(10) 

In This Article

Long-Term Follow-Up

The goal of long-term follow-up is to detect untreated residual and recurrent tumor when it is small and potentially treatable (Figure 6). Patients are also followed to identify development of any extrahepatic disease. Any one or a combination of the imaging modalities (CT, MRI, and/or US) may be used for follow-up. The choice of modality is based on patient concerns (eg, contrast-media-related allergy, renal status, and clinical availability) and operator experience. We recommend that follow-up should be performed with the same imaging performed prior to treatment, as this will allow for accurate comparison of findings.

A 45-year-old woman with hepatocellular carcinoma. (A) Preprocedural contrast-enhanced CT scan shows a hypervascular lesion in the right lobe of the liver. (B) Preprocedural ultrasound (US) shows the mass as a hypoechoic lesion (between the cursors). Ultrasound-guided ablation was performed. (C) CT scan performed at 1-month follow-up shows residual tumor represented by soft-issue density lying anteriorly in the low-attenuation ablation area. Repeat radiofrequency ablation was performed using combined US and CT guidance. (D) CT scan at 6-month follow-up shows complete tumor necrosis and no evidence of recurrence.

A 45-year-old woman with hepatocellular carcinoma. (A) Preprocedural contrast-enhanced CT scan shows a hypervascular lesion in the right lobe of the liver. (B) Preprocedural ultrasound (US) shows the mass as a hypoechoic lesion (between the cursors). Ultrasound-guided ablation was performed. (C) CT scan performed at 1-month follow-up shows residual tumor represented by soft-issue density lying anteriorly in the low-attenuation ablation area. Repeat radiofrequency ablation was performed using combined US and CT guidance. (D) CT scan at 6-month follow-up shows complete tumor necrosis and no evidence of recurrence.

A 45-year-old woman with hepatocellular carcinoma. (A) Preprocedural contrast-enhanced CT scan shows a hypervascular lesion in the right lobe of the liver. (B) Preprocedural ultrasound (US) shows the mass as a hypoechoic lesion (between the cursors). Ultrasound-guided ablation was performed. (C) CT scan performed at 1-month follow-up shows residual tumor represented by soft-issue density lying anteriorly in the low-attenuation ablation area. Repeat radiofrequency ablation was performed using combined US and CT guidance. (D) CT scan at 6-month follow-up shows complete tumor necrosis and no evidence of recurrence.

A 45-year-old woman with hepatocellular carcinoma. (A) Preprocedural contrast-enhanced CT scan shows a hypervascular lesion in the right lobe of the liver. (B) Preprocedural ultrasound (US) shows the mass as a hypoechoic lesion (between the cursors). Ultrasound-guided ablation was performed. (C) CT scan performed at 1-month follow-up shows residual tumor represented by soft-issue density lying anteriorly in the low-attenuation ablation area. Repeat radiofrequency ablation was performed using combined US and CT guidance. (D) CT scan at 6-month follow-up shows complete tumor necrosis and no evidence of recurrence.

On CT scans, complete ablation is seen as a low-attenuation area devoid of enhancement or nodules, as described earlier. Hepatic arterial-phase images are useful in evaluating hypervascular HCC and portal venous-phase images are useful in evaluating metastases. On MR imaging, the ablated tissue demonstrates low signal and there is lack of enhancement in dynamic contrast-enhanced sequences. Bright signal on T2-weighted images and nodular contrast enhancement are suggestive of viable tumor tissue. In the early postoperative period, there is contrast enhancement of the rim or interface. The finding usually persists for a few weeks, usually disappearing by 4 weeks on CT and possibly persisting for few months on contrast-enhanced MR. Another important finding of complete ablation is that the size of the defect remains stable or decreases over time. Any increase in size is suspicious for tumor recurrence.

The follow-up sequence most commonly used is to obtain scans immediately after the procedure (within 24 hours) followed by scans at 1 month, 3 months, and then every 3 months. It is also useful to obtain serum alpha-fetoprotein or carcinoembryonic antigen, as appropriate, at 3 monthly intervals in HCC and colorectal metastasis. Ideally, the follow-up should be continued indefinitely since tumors are known to recur even after months.

Two other imaging techniques used for follow-up need special mention: contrast-enhanced US and functional positron emission tomography (PET) imaging.[43,49] Unenhanced color and power Doppler US do not reliably detect residual or recurrent tumor.[41,50] However, combining US contrast agents with the Doppler technique improves detection of residual or recurrent tumor.[43,44] Recent studies suggest that the addition of harmonic imaging to contrast-enhanced Doppler techniques can improve accuracy levels comparable to that of triple-phase CT scanning.[46,47,51] With 18-fluorodeoxyglucose (18-FDG)-labeled PET scanning, abnormal increased activity after ablation has been reported to represent residual or recurrent tumor.[49] However, the experience is still limited, and this modality cannot be recommended for routine follow up.

Percutaneous biopsy is another potential tool in diagnosing tumor recurrence. Imaging findings are usually sufficient to diagnose residual or recurrent tumor. If there is any discrepancy between clinical and imaging findings or if the imaging findings are not diagnostic, the suspicious area should be biopsied. Biopsy is not routinely recommended because of its limitations, such as sampling error and limited experience in interpretation of biopsy specimens with heat-induced damage. Thus, a negative biopsy does not guarantee complete treatment.[52] Similarly, imaging techniques also have limitations. The resolution of the current scanners is only 2 to 3 mm, making it difficult to diagnose microscopic residual or recurrent tumor, and to differentiate a small recurrence from ablation-induced hyperemia in the early postprocedural period.[53] Therefore, optimal follow-up protocol will include anatomic and functional imaging, and image-guided biopsy when the imaging findings are not definite or when a discrepancy exists between clinical and imaging findings.

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