(Radiographics. 2001;21:S41-S54.)
© RSNA, 2001
Helping the Hepatic Surgeon |
Radio-frequency Ablation of Liver Tumors: Assessment of Therapeutic Response and Complications1
Haesun Choi, MD,
Evelyne M. Loyer, MD,
Ronelle A. DuBrow, MD,
Harmeet Kaur, MD,
Cynthia L. David, MD,
Steven Huang, MD,
Steven Curley, MD and
Chusilp Charnsangavej, MD
1 From the Divisions of Diagnostic Imaging (H.C., E.M.L., R.A.D., H.K., C.L.D., S.H., C.C.) and Surgical Oncology (S.C.), University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd, Box 57, Houston, TX 77030. Recipient of a Cum Laude award for an education exhibit at the 2000 RSNA scientific assembly. Received February 9, 2001; revision requested April 11 and received May 16; accepted May 29. Address correspondence to E.M.L. (e-mail: eloyer@di.mdacc.tmc.edu).
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Abstract
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An alternative to surgical resection of liver tumors, radio-frequency ablation induces in situ thermal coagulation necrosis through the delivery of high-frequency alternating current to the tissues. Imaging helps to detect treatable lesions, guide the placement of the probe, and assess the effect of therapy. Computed tomography (CT) is used most frequently to determine whether the ablation is complete and to screen for early recurrences that may benefit from reablation. Complete ablation creates an area of necrosis that, at CT, is of low attenuation compared with the surrounding liver tissue, is often homogeneous, and has smooth margins. The most important features are the size of the necrotic defect, which, immediately after treatment, should be larger than that of the pretreatment tumor, and the sharpness of the margins, which indicates an abrupt change in attenuation between the necrotic tissue and surrounding liver tissue. Enhancement, when present, is due to perfusion abnormality or granulation tissue and forms a regular rim or a homogeneous zone at the margin of the defect. It is seen immediately after ablation but may be prolonged. Enhancement is affected by the scanning technique. Over time, the size of the defect remains stable or decreases. Any variation from this general pattern is suggestive of incomplete ablation or recurrence.
Index Terms: Liver neoplasms, CT, 761.12114 • Liver neoplasms, MR, 761.12141 • Liver neoplasms, therapy, 761.30, 761.1269 • Radiofrequency (RF) ablation, 761.1269
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LEARNING OBJECTIVES FOR TEST 2
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After reading this article and taking the test, the reader will be able to:
- Define the basic concept of radio-frequency ablation of the liver.
- List the imaging criteria of complete radio-frequency ablation and recurrent or residual disease.
- Describe the imaging features of possible complications.
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Introduction
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Surgical resection provides the greatest potential for cure in patients with primary or secondary liver tumors but can be offered to only a small number of patients. Patients with too many lesions or with lesions that are unresectable owing to their location and patients with insufficient liver reserve or comorbid conditions are not eligible. In addition, long-term outcome for those who undergo surgery, while improved significantly, is not uniformly successful, with survival rates ranging from 25% to 40% at 5 years (1,2).
The development of nonsurgical, local ablative techniques has provided a new therapeutic option, which, like surgery, aims at the complete eradication of a tumor (3). With this approach, numerous lesions or lesions in unresectable locations are no longer a strict contraindication to an attempt at curative treatment, and recurrences may also be amenable to treatment. Radio-frequency ablation is the most promising of these techniques (4,5). Current clinical experience suggests that it is effective, safe, and relatively simple (6–15). With this method, high-frequency alternating current is delivered to the tissue via a needle electrode. The electric current agitates the ions in the tissue around the tip of the electrode, creating heat, which leads to localized coagulation necrosis (4,5).
Radio-frequency ablation is limited, however. With currently available devices, the largest focus of necrosis that can be induced with a single application is approximately 4–5 cm in greatest diameter. Thus, the diameter of suitable lesions must be less than 3–4 cm unless placement of multiple probes or an adjuvant technique is performed (6). Concomitant decrease of the arterial supply to the tumor with balloon occlusion or embolization or at laparotomy with temporary occlusion of the hepatic inflow (Pringle maneuver) increases necrosis (14,15). Other limitations are the proximity of the tumors to large vessels, which may prevent adequate heating, as well as proximity to central bile ducts, which predisposes the patient to a risk of biliary complications. Finally, treatment of superficially located tumors carries a risk of injury to adjacent abdominal organs or the diaphragm (4) (Fig 1).
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Figure 1a. Complete ablation in a 65-year-old woman with metastatic colon carcinoma. (a) CT scan obtained before ablation shows a metastatic lesion in segment V (arrow). Because the duodenum abuts the lesion, the percutaneous approach would bear the risk of bowel injury. (b) CT scan obtained 1 month after ablation shows a low-attenuation defect (arrow) larger than the pretreatment metastasis and with a smooth margin. (c, d) Subsequent scans show that the defect gradually decreases in size (arrow) over time, with smooth margins persisting 3 (c) and 9 (d) months after ablation.
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Figure 1b. Complete ablation in a 65-year-old woman with metastatic colon carcinoma. (a) CT scan obtained before ablation shows a metastatic lesion in segment V (arrow). Because the duodenum abuts the lesion, the percutaneous approach would bear the risk of bowel injury. (b) CT scan obtained 1 month after ablation shows a low-attenuation defect (arrow) larger than the pretreatment metastasis and with a smooth margin. (c, d) Subsequent scans show that the defect gradually decreases in size (arrow) over time, with smooth margins persisting 3 (c) and 9 (d) months after ablation.
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Figure 1c. Complete ablation in a 65-year-old woman with metastatic colon carcinoma. (a) CT scan obtained before ablation shows a metastatic lesion in segment V (arrow). Because the duodenum abuts the lesion, the percutaneous approach would bear the risk of bowel injury. (b) CT scan obtained 1 month after ablation shows a low-attenuation defect (arrow) larger than the pretreatment metastasis and with a smooth margin. (c, d) Subsequent scans show that the defect gradually decreases in size (arrow) over time, with smooth margins persisting 3 (c) and 9 (d) months after ablation.
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Figure 1d. Complete ablation in a 65-year-old woman with metastatic colon carcinoma. (a) CT scan obtained before ablation shows a metastatic lesion in segment V (arrow). Because the duodenum abuts the lesion, the percutaneous approach would bear the risk of bowel injury. (b) CT scan obtained 1 month after ablation shows a low-attenuation defect (arrow) larger than the pretreatment metastasis and with a smooth margin. (c, d) Subsequent scans show that the defect gradually decreases in size (arrow) over time, with smooth margins persisting 3 (c) and 9 (d) months after ablation.
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Radio-frequency ablation can be performed percutaneously, at laparoscopy, or at laparotomy and may be performed along with liver resection. The technique used varies with the investigators. The principal advantage of surgical rather than percutaneous radio-frequency ablation is the improved staging with intraoperative ultrasonography (US) and assessment for the presence of extrahepatic disease. The radio-frequency needle may be placed with US, computed tomographic (CT), or magnetic resonance (MR) imaging guidance when the transabdominal approach is used and with US guidance when laparoscopic or open surgical approaches are used (4,5).
Imaging after the procedure is crucial to judge the completeness of the ablation and later on to detect early recurrences, which may be amenable to repeated ablation. This assessment is usually performed with CT, although MR imaging is equally accurate (16). Some investigators use US to monitor immediate results with hypervascular tumors (17).
The increasing use of radio-frequency ablation at our institution led us to review our experience to establish guidelines for the interpretation of the postprocedure imaging studies, primarily CT. This article, based on our daily experience, is not a prospective nor a systematic retrospective study focused on the value of radio-frequency ablation as a therapeutic method, but a description of the morphologic consequences of the procedure. Our purpose was primarily to emphasize, based on examples, the need for precise analysis of the tumor margins and to draw attention to subtle findings of local recurrence or residual tumor that may be overlooked if careful serial comparison is not performed.
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Materials and Methods
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We reviewed posttreatment studies obtained in 70 patients who underwent treatment between 1997 and 2000 for hepatic metastasis or primary liver tumors. The population studied is heterogeneous in that the first 25 patients underwent treatment when radio-frequency ablation was first introduced (phase 1 study) and the selection of remaining patients was based essentially on the availability of pretreatment studies and follow-up at the time the review was performed. The patients were part of a larger cohort that included 281 who underwent treatment and follow-up at our institution. Radio-frequency ablation was for the most part performed at laparotomy. Criteria for patient selection and management are described elsewhere (14).
Posttreatment imaging was performed with CT and, less frequently, MR imaging. CT was performed with a HiSpeed Advantage scanner or Lightspeed scanner (GE Medical Systems, Milwaukee, Wis). First, unenhanced axial scans with 10-mm collimation were acquired. Then, contrast-enhanced helical CT of the liver was performed during a single breath hold with the use of either a single-phase protocol in which images were acquired 70 seconds after the start of injection or a triphase liver protocol in which images were acquired 20 seconds, 55 seconds, and approximately 1–2 minutes after the start of injection of 150 mL of ioversol (Optiray; Mallinckrodt, St Louis, Mo) at a rate of 5 mL/sec or 30 seconds, 65 seconds, and approximately 2 minutes after the start of injection if the rate was 3 mL/sec. Collimation was 5 or 7 mm, with a pitch of 2:1 for the HiSpeed unit and a pitch of 6 with a speed of 15 mm per rotation for the Lightspeed unit.
The indication for one or the other technique evolved over time. When radio-frequency ablation was first introduced, patients underwent a dedicated liver protocol regardless of the underlying pathologic condition. Now, because a clear benefit for this approach was not found clinically, only patients who have undergone treatment for a hypervascular tumor undergo routine follow-up with a liver protocol.
Timing for follow-up studies has also evolved over time. Early on, follow-up was performed 1–4 weeks after radio-frequency ablation, again at 3 months, and every 3 months thereafter. Now, most patients undergo imaging 3 months after treatment and subsequently every 3 months.
MR imaging is used for follow-up when a patient is allergic to iodine. It is also used as a problem-solving modality when, for example, a discrepancy exists between clinical results and the findings at CT or when a lesion is suspected at CT but is not definite. Experience with positron emission tomography is, in this setting, limited to one case in which it was used in the face of a rising level of carcinoembryonic antigen unexplainable from the findings at CT.
Pretreatment and all available posttreatment studies were reviewed. One hundred thirty-nine lesions in 70 patients were assessed for attenuation characteristics of the liquefied content, sharpness of margins, and peripheral enhancement. Morphologic changes attributable to the therapy, such as biliary stenosis, fistula, or vascular abnormalities, were also recorded. The median follow-up was 10 months.
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Complete Ablation
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The ablation procedure creates an area of necrosis within the liver parenchyma. Before intravenous administration of contrast medium, the necrosis is of low attenuation in comparison with the surrounding liver parenchyma but often contains areas of higher attenuation that correspond to regions where cellular disruption is greater (Fig 2a) (18). These high-attenuation areas resolve at a variable rate in the following weeks or months. In five of 139 treated lesions, the necrosis contained gas (Fig 2b), which resolved spontaneously but could still be seen in one case 3 months after the procedure. The presence of gas suggests the possibility of an abscess. Whether drainage is necessary, however, will be based on clinical information.
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Figure 2a. Early changes after complete radio-frequency ablation in a 32-year-old man. (a) Unenhanced CT scan obtained 3 months after the ablation procedure shows high-attenuation hemorrhage within the low-attenuation defects in segments III (arrowheads) and IV and VIII (arrow). (b) CT scan obtained 1 month after ablation shows gas in the defect. Diffuse peripheral enhancement (arrows) indicates hyperemia.
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Figure 2b. Early changes after complete radio-frequency ablation in a 32-year-old man. (a) Unenhanced CT scan obtained 3 months after the ablation procedure shows high-attenuation hemorrhage within the low-attenuation defects in segments III (arrowheads) and IV and VIII (arrow). (b) CT scan obtained 1 month after ablation shows gas in the defect. Diffuse peripheral enhancement (arrows) indicates hyperemia.
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The shape of the radio-frequency defect is variable, often round or ovoid, sometimes with a more complex geometric shape determined from needle placements or the proximity of a large vessel. The most important morphologic features of complete ablation are the size and characteristic smooth margins of the defect. The defect should be centered on and, at early follow-up, larger than the treated tumor to ensure tumor-free margins. The interface between the liver and the lesion should be sharp. This interface is best assessed after administration of contrast medium, when an abrupt change between the unenhanced necrotic tissue and adjacent parenchyma can be defined (Fig 1). Any variation from this pattern is suspicious for residual or recurrent tumor. These morphologic characteristics of the radio-frequency ablation defect have been observed by others (5,9–11) and apply to MR imaging as well. Specific to MR imaging are changes in signal intensity. On T2-weighted images, the treated tumor is characterized by low signal intensity, whereas viable tumor tissue produces high signal intensity (16). At early follow-up, necrotic debris within the defect often produces heterogeneous high signal intensity and a hypointense rim on T2-weighted MR images (Fig 3).
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Figure 3a. Complete ablation in a 72-year-old woman with metastatic breast carcinoma. (a-c) MR images obtained 1 week after radio-frequency ablation show a heterogeneous ablation defect (arrows in a, b) with internal hemorrhage at T1 weighting (a) and fat-saturated fast-spin-echo T2 weighting (b) and rim enhancement (arrowheads in c) at enhanced T1 weighting (c). (d) Fat-saturated fast-spin-echo T2-weighted image obtained 6 months after ablation shows the defect has decreased in size and has only slight high signal intensity posteriorly (arrow) and low signal intensity anteriorly (arrowhead). (e) Enhanced T1-weighted MR image obtained at the same time as d shows near resolution of the rim enhancement (arrowheads) and no significant enhancement within the ablation defect. (f) On a fat-saturated fast-spin-echo T2-weighted MR image, the defect has become less conspicuous (arrow) at 1.5 years after ablation.
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Figure 3b. Complete ablation in a 72-year-old woman with metastatic breast carcinoma. (a-c) MR images obtained 1 week after radio-frequency ablation show a heterogeneous ablation defect (arrows in a, b) with internal hemorrhage at T1 weighting (a) and fat-saturated fast-spin-echo T2 weighting (b) and rim enhancement (arrowheads in c) at enhanced T1 weighting (c). (d) Fat-saturated fast-spin-echo T2-weighted image obtained 6 months after ablation shows the defect has decreased in size and has only slight high signal intensity posteriorly (arrow) and low signal intensity anteriorly (arrowhead). (e) Enhanced T1-weighted MR image obtained at the same time as d shows near resolution of the rim enhancement (arrowheads) and no significant enhancement within the ablation defect. (f) On a fat-saturated fast-spin-echo T2-weighted MR image, the defect has become less conspicuous (arrow) at 1.5 years after ablation.
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Figure 3c. Complete ablation in a 72-year-old woman with metastatic breast carcinoma. (a-c) MR images obtained 1 week after radio-frequency ablation show a heterogeneous ablation defect (arrows in a, b) with internal hemorrhage at T1 weighting (a) and fat-saturated fast-spin-echo T2 weighting (b) and rim enhancement (arrowheads in c) at enhanced T1 weighting (c). (d) Fat-saturated fast-spin-echo T2-weighted image obtained 6 months after ablation shows the defect has decreased in size and has only slight high signal intensity posteriorly (arrow) and low signal intensity anteriorly (arrowhead). (e) Enhanced T1-weighted MR image obtained at the same time as d shows near resolution of the rim enhancement (arrowheads) and no significant enhancement within the ablation defect. (f) On a fat-saturated fast-spin-echo T2-weighted MR image, the defect has become less conspicuous (arrow) at 1.5 years after ablation.
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Figure 3d. Complete ablation in a 72-year-old woman with metastatic breast carcinoma. (a-c) MR images obtained 1 week after radio-frequency ablation show a heterogeneous ablation defect (arrows in a, b) with internal hemorrhage at T1 weighting (a) and fat-saturated fast-spin-echo T2 weighting (b) and rim enhancement (arrowheads in c) at enhanced T1 weighting (c). (d) Fat-saturated fast-spin-echo T2-weighted image obtained 6 months after ablation shows the defect has decreased in size and has only slight high signal intensity posteriorly (arrow) and low signal intensity anteriorly (arrowhead). (e) Enhanced T1-weighted MR image obtained at the same time as d shows near resolution of the rim enhancement (arrowheads) and no significant enhancement within the ablation defect. (f) On a fat-saturated fast-spin-echo T2-weighted MR image, the defect has become less conspicuous (arrow) at 1.5 years after ablation.
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Figure 3e. Complete ablation in a 72-year-old woman with metastatic breast carcinoma. (a-c) MR images obtained 1 week after radio-frequency ablation show a heterogeneous ablation defect (arrows in a, b) with internal hemorrhage at T1 weighting (a) and fat-saturated fast-spin-echo T2 weighting (b) and rim enhancement (arrowheads in c) at enhanced T1 weighting (c). (d) Fat-saturated fast-spin-echo T2-weighted image obtained 6 months after ablation shows the defect has decreased in size and has only slight high signal intensity posteriorly (arrow) and low signal intensity anteriorly (arrowhead). (e) Enhanced T1-weighted MR image obtained at the same time as d shows near resolution of the rim enhancement (arrowheads) and no significant enhancement within the ablation defect. (f) On a fat-saturated fast-spin-echo T2-weighted MR image, the defect has become less conspicuous (arrow) at 1.5 years after ablation.
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Figure 3f. Complete ablation in a 72-year-old woman with metastatic breast carcinoma. (a-c) MR images obtained 1 week after radio-frequency ablation show a heterogeneous ablation defect (arrows in a, b) with internal hemorrhage at T1 weighting (a) and fat-saturated fast-spin-echo T2 weighting (b) and rim enhancement (arrowheads in c) at enhanced T1 weighting (c). (d) Fat-saturated fast-spin-echo T2-weighted image obtained 6 months after ablation shows the defect has decreased in size and has only slight high signal intensity posteriorly (arrow) and low signal intensity anteriorly (arrowhead). (e) Enhanced T1-weighted MR image obtained at the same time as d shows near resolution of the rim enhancement (arrowheads) and no significant enhancement within the ablation defect. (f) On a fat-saturated fast-spin-echo T2-weighted MR image, the defect has become less conspicuous (arrow) at 1.5 years after ablation.
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After administration of contrast medium, completely ablated lesions show no enhancement within the necrotic area, but enhancement at the periphery of the defect may be a normal finding that can be a source of diagnostic difficulties. We observed peripheral enhancement in only 10 lesions of 139 reviewed. Peripheral nontumoral enhancement is variable in intensity and thickness but as a rule is devoid of nodularity and forms a circumferential homogeneous rim at the periphery of the treated tumor (Fig 4). Its appearance is affected by the scanning technique. In one of our patients, however, a persistent nodule of enhancement at the margin of the radio-frequency ablation defect was benign (Fig 5). Peripheral enhancement at CT or MR imaging is observed immediately after the procedure (4,11) and disappears over time. We observed enhancement up to 3 months after ablation. Goldberg et al (19) illustrate peripheral enhancement 6 months after ablation. Similar findings have been reported with other ablative techniques (20–22). Nontumoral enhancement corresponds to congestion or granulation tissue. Histopathologic examination in animal studies has shown a peripheral zone of congestion and sinusoidal hemorrhage immediately after cryoablation and a layer of granulation tissue 5 weeks later (20).
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Figure 4a. Benign peripheral enhancement in a 61-year-old man. (a) CT scan obtained 3 weeks after radio-frequency ablation shows a smooth, thin, regular rim of enhancement (arrow) along the ablation defect that is consistent with granulation tissue. (b) CT scan obtained 6 months after ablation shows that the defect (arrow) has decreased in size and rim enhancement is no longer present.
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Figure 4b. Benign peripheral enhancement in a 61-year-old man. (a) CT scan obtained 3 weeks after radio-frequency ablation shows a smooth, thin, regular rim of enhancement (arrow) along the ablation defect that is consistent with granulation tissue. (b) CT scan obtained 6 months after ablation shows that the defect (arrow) has decreased in size and rim enhancement is no longer present.
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Figure 5a. Benign nodular enhancement mimicking recurrent disease in a 71-year-old man with hepatocellular carcinoma. (a) Preablation CT scan shows a hypervascular lesion (arrow) in segment IV. (b) CT scan obtained 2 months after ablation shows an enhancing nodule (arrow) at the margin of the ablation defect. This nodule remained stable for more than 1 year. (c, d) Arterial-phase (c) and portal-venous-phase (d) CT images obtained at 2.5 years after ablation show that the nodule has disappeared. The patient remained free of disease.
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Figure 5b. Benign nodular enhancement mimicking recurrent disease in a 71-year-old man with hepatocellular carcinoma. (a) Preablation CT scan shows a hypervascular lesion (arrow) in segment IV. (b) CT scan obtained 2 months after ablation shows an enhancing nodule (arrow) at the margin of the ablation defect. This nodule remained stable for more than 1 year. (c, d) Arterial-phase (c) and portal-venous-phase (d) CT images obtained at 2.5 years after ablation show that the nodule has disappeared. The patient remained free of disease.
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Figure 5c. Benign nodular enhancement mimicking recurrent disease in a 71-year-old man with hepatocellular carcinoma. (a) Preablation CT scan shows a hypervascular lesion (arrow) in segment IV. (b) CT scan obtained 2 months after ablation shows an enhancing nodule (arrow) at the margin of the ablation defect. This nodule remained stable for more than 1 year. (c, d) Arterial-phase (c) and portal-venous-phase (d) CT images obtained at 2.5 years after ablation show that the nodule has disappeared. The patient remained free of disease.
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Figure 5d. Benign nodular enhancement mimicking recurrent disease in a 71-year-old man with hepatocellular carcinoma. (a) Preablation CT scan shows a hypervascular lesion (arrow) in segment IV. (b) CT scan obtained 2 months after ablation shows an enhancing nodule (arrow) at the margin of the ablation defect. This nodule remained stable for more than 1 year. (c, d) Arterial-phase (c) and portal-venous-phase (d) CT images obtained at 2.5 years after ablation show that the nodule has disappeared. The patient remained free of disease.
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In two patients, liver resection prompted by the demonstration of a region of enhancement 6 months after radio-frequency ablation revealed vascular fibrotic tissue but no tumor (16). From the practical standpoint, several elements besides the lack of nodularity help differentiate residual or recurrent tumor tissue from peripheral reactive inflammation or perfusion abnormality. At early follow-up, the enhancement should be clearly beyond the confines of the pretreatment tumor. With a multiphasic technique, hypervascular tumor tissue tends to enhance early and briefly. These tumors may become hypoattenuating compared with the surrounding parenchyma while zones of perfusion abnormalities or fibrosis become, respectively, isoattenuating or hyperattenuating over time (23).
Another important criterion for complete ablation is the evolution over time of the size of the defect (Fig 1). While the evolution is unpredictable, if the ablation is complete, the size can only remain stable or decrease. Any enlargement represents tumor growth (20).
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Incomplete Ablation and Local Recurrence
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Incomplete ablation and local recurrence have identical appearances at CT and MR imaging; only from the clinical context can they be differentiated.
The radiologic findings can be anticipated from the criteria that define complete ablation. Tumor tissue may be obvious as an area of nodular low attenuation or enhancement that abuts or surrounds the defect or protrudes into the necrotic tissue.
Residual or recurrent disease may be subtle and most often occurs at the periphery of the defect. Recurrent or residual hypovascular tumor tissue produces a distortion of the otherwise smooth interface with the liver parenchyma (Figs 6, 7). It may be a small nodule of only slightly higher attenuation than the necrotic tissue that protrudes within the defect or a faint hypoattenuating zone that extends into the adjacent parenchyma (Fig 8). An indirect sign may be a smaller size and, sometimes, eccentric location of the defect in comparison with the original lesion. Apparent enlargement of the defect is consistent with recurrence (Fig 6).
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Figure 6a. Local recurrence in a 56-year-old woman with metastatic colon carcinoma. (a, b) CT scans obtained 17 (a) and 23 (b) months after radio-frequency ablation show an apparent increase in the size of the ablation defect in segment VIII, which indicates recurrence. The area of low attenuation extends behind the right hepatic vein (arrowhead in b). The small lymph node near the esophagus (arrow) has enlarged. (c, d) Fat-saturated fast-spin-echo T2-weighted MR image (c) and positron emission tomographic scan (d) obtained 24 months after ablation help confirm the local recurrence (arrowhead) at the posterior aspect of the hypointense ablation defect (arrow in c).
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Figure 6b. Local recurrence in a 56-year-old woman with metastatic colon carcinoma. (a, b) CT scans obtained 17 (a) and 23 (b) months after radio-frequency ablation show an apparent increase in the size of the ablation defect in segment VIII, which indicates recurrence. The area of low attenuation extends behind the right hepatic vein (arrowhead in b). The small lymph node near the esophagus (arrow) has enlarged. (c, d) Fat-saturated fast-spin-echo T2-weighted MR image (c) and positron emission tomographic scan (d) obtained 24 months after ablation help confirm the local recurrence (arrowhead) at the posterior aspect of the hypointense ablation defect (arrow in c).
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Figure 6c. Local recurrence in a 56-year-old woman with metastatic colon carcinoma. (a, b) CT scans obtained 17 (a) and 23 (b) months after radio-frequency ablation show an apparent increase in the size of the ablation defect in segment VIII, which indicates recurrence. The area of low attenuation extends behind the right hepatic vein (arrowhead in b). The small lymph node near the esophagus (arrow) has enlarged. (c, d) Fat-saturated fast-spin-echo T2-weighted MR image (c) and positron emission tomographic scan (d) obtained 24 months after ablation help confirm the local recurrence (arrowhead) at the posterior aspect of the hypointense ablation defect (arrow in c).
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Figure 6d. Local recurrence in a 56-year-old woman with metastatic colon carcinoma. (a, b) CT scans obtained 17 (a) and 23 (b) months after radio-frequency ablation show an apparent increase in the size of the ablation defect in segment VIII, which indicates recurrence. The area of low attenuation extends behind the right hepatic vein (arrowhead in b). The small lymph node near the esophagus (arrow) has enlarged. (c, d) Fat-saturated fast-spin-echo T2-weighted MR image (c) and positron emission tomographic scan (d) obtained 24 months after ablation help confirm the local recurrence (arrowhead) at the posterior aspect of the hypointense ablation defect (arrow in c).
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Figure 7a. Local recurrence in a 56-year-old woman with cholangiocarcinoma. (a) CT scan obtained 2 months after radio-frequency ablation shows a completely ablated lesion (arrows) in segment IV. (b) CT scan obtained 5 months after ablation shows a new area of low attenuation (arrowhead) adjacent to the left portal vein (LPV) and change in the contour of the liver in segment III (arrow), findings indicating recurrence. (c) CT scan obtained at 8 months shows that the disease has progressed at both sites (white arrow and arrowhead). In addition, a new lesion (black arrow) is in the lateral segment.
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Figure 7b. Local recurrence in a 56-year-old woman with cholangiocarcinoma. (a) CT scan obtained 2 months after radio-frequency ablation shows a completely ablated lesion (arrows) in segment IV. (b) CT scan obtained 5 months after ablation shows a new area of low attenuation (arrowhead) adjacent to the left portal vein (LPV) and change in the contour of the liver in segment III (arrow), findings indicating recurrence. (c) CT scan obtained at 8 months shows that the disease has progressed at both sites (white arrow and arrowhead). In addition, a new lesion (black arrow) is in the lateral segment.
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Figure 7c. Local recurrence in a 56-year-old woman with cholangiocarcinoma. (a) CT scan obtained 2 months after radio-frequency ablation shows a completely ablated lesion (arrows) in segment IV. (b) CT scan obtained 5 months after ablation shows a new area of low attenuation (arrowhead) adjacent to the left portal vein (LPV) and change in the contour of the liver in segment III (arrow), findings indicating recurrence. (c) CT scan obtained at 8 months shows that the disease has progressed at both sites (white arrow and arrowhead). In addition, a new lesion (black arrow) is in the lateral segment.
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Figure 8a. Incomplete ablation and local recurrence in a 66-year-old man with metastatic rectal carcinoma. (a) CT scan obtained 1 month after radio-frequency ablation shows a subtle soft-tissue nodule (arrow) that protrudes into the ablation defect in segment VII, which indicates incomplete ablation. Ablation in segment VIII (arrowhead) was considered to be complete. (b, c) CT scans obtained 2 months after ablation show an enlarging tumor in segment VII (arrow in b) and local recurrence in segment VIII (arrowhead in c) at a slightly lower level. The ablation defect in segment VIII has increased in size and the contour is irregular.
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Figure 8b. Incomplete ablation and local recurrence in a 66-year-old man with metastatic rectal carcinoma. (a) CT scan obtained 1 month after radio-frequency ablation shows a subtle soft-tissue nodule (arrow) that protrudes into the ablation defect in segment VII, which indicates incomplete ablation. Ablation in segment VIII (arrowhead) was considered to be complete. (b, c) CT scans obtained 2 months after ablation show an enlarging tumor in segment VII (arrow in b) and local recurrence in segment VIII (arrowhead in c) at a slightly lower level. The ablation defect in segment VIII has increased in size and the contour is irregular.
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Figure 8c. Incomplete ablation and local recurrence in a 66-year-old man with metastatic rectal carcinoma. (a) CT scan obtained 1 month after radio-frequency ablation shows a subtle soft-tissue nodule (arrow) that protrudes into the ablation defect in segment VII, which indicates incomplete ablation. Ablation in segment VIII (arrowhead) was considered to be complete. (b, c) CT scans obtained 2 months after ablation show an enlarging tumor in segment VII (arrow in b) and local recurrence in segment VIII (arrowhead in c) at a slightly lower level. The ablation defect in segment VIII has increased in size and the contour is irregular.
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Enhancement at the periphery of the residual or recurrent tumor may be present, just as it is often seen with adenocarcinoma at initial presentation (Fig 9). Recurrence of hypervascular tumor tissue may sometimes be seen only during the arterial phase of a multiphasic liver protocol. This fact emphasizes the importance of scanning technique (Fig 10) (4).
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Figure 9a. Incomplete ablation and local recurrence in a 62-year-old woman with metastatic colon carcinoma. (a) CT scan obtained 1 week after radio-frequency ablation shows an ablation defect in segment III with an irregular rim of enhancement (arrowhead). More diffuse, ill-defined enhancement (arrow) is around the defect in segments IV and VIII. These findings are indeterminate. (b) CT scan obtained 6 weeks after ablation shows complete ablation in segment III (arrowhead), with resolution of the enhancing rim. The margin of the low-attenuation defect is smooth. In segments IV and VIII, recurrence or incomplete ablation (arrow) is seen as a low-attenuation margin along the border of the defect.
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Figure 9b. Incomplete ablation and local recurrence in a 62-year-old woman with metastatic colon carcinoma. (a) CT scan obtained 1 week after radio-frequency ablation shows an ablation defect in segment III with an irregular rim of enhancement (arrowhead). More diffuse, ill-defined enhancement (arrow) is around the defect in segments IV and VIII. These findings are indeterminate. (b) CT scan obtained 6 weeks after ablation shows complete ablation in segment III (arrowhead), with resolution of the enhancing rim. The margin of the low-attenuation defect is smooth. In segments IV and VIII, recurrence or incomplete ablation (arrow) is seen as a low-attenuation margin along the border of the defect.
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Figure 10a. Recurrent disease not seen during portal-phase imaging in a 33-year-old woman with metastatic neuroendocrine tumor of the pancreas. (a) CT scan obtained before ablation shows a metastatic lesion (arrow) in segment VII. (b) Six months after radio-frequency ablation, arterial-phase scan obtained during triphasic CT shows recurrence (arrow) along the margin of the ablation defect. (c) Portal-phase CT scan obtained at the same time as b shows no hypervascular tumor.
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Figure 10b. Recurrent disease not seen during portal-phase imaging in a 33-year-old woman with metastatic neuroendocrine tumor of the pancreas. (a) CT scan obtained before ablation shows a metastatic lesion (arrow) in segment VII. (b) Six months after radio-frequency ablation, arterial-phase scan obtained during triphasic CT shows recurrence (arrow) along the margin of the ablation defect. (c) Portal-phase CT scan obtained at the same time as b shows no hypervascular tumor.
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Figure 10c. Recurrent disease not seen during portal-phase imaging in a 33-year-old woman with metastatic neuroendocrine tumor of the pancreas. (a) CT scan obtained before ablation shows a metastatic lesion (arrow) in segment VII. (b) Six months after radio-frequency ablation, arterial-phase scan obtained during triphasic CT shows recurrence (arrow) along the margin of the ablation defect. (c) Portal-phase CT scan obtained at the same time as b shows no hypervascular tumor.
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Follow-up CT or MR images are also scrutinized for new hepatic metastasis (Fig 7) and extrahepatic tumors (Fig 11). In a recent review of patients who underwent treatment at our institution, new liver or extrahepatic metastasis accounted for the majority of recurrences, with a rate of 47% compared with a rate of 9% for local recurrence (24).
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Figure 11a. Recurrent disease with distant metastasis in a 56-year-old woman with metastatic colon carcinoma. CT scans obtained 1 (a) and 3.5 (b) months after radio-frequency ablation show complete ablation of a lesion (arrowheads) at the dome of the liver with no local recurrence. The postsurgical perihepatic fluid and pleural effusion resolved as well. However, at 3.5 months, nodal metastasis (arrow in b) is seen.
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Figure 11b. Recurrent disease with distant metastasis in a 56-year-old woman with metastatic colon carcinoma. CT scans obtained 1 (a) and 3.5 (b) months after radio-frequency ablation show complete ablation of a lesion (arrowheads) at the dome of the liver with no local recurrence. The postsurgical perihepatic fluid and pleural effusion resolved as well. However, at 3.5 months, nodal metastasis (arrow in b) is seen.
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Complications
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The complication rate reported in published series is low and makes radio-frequency ablation a relatively safe procedure. Complications relevant to the radiologist are bleeding; injury to blood vessels, bile ducts, the diaphragm, or abdominal organs; and infection. Patients who undergo treatment at laparotomy are also exposed to the risks inherent in general anesthesia and abdominal exploration. Intrahepatic (4,25), perihepatic, intraperitoneal (9,11), and intrapleural hemorrhage have been reported. Intrahepatic abscesses were observed in two instances (4,26). Cholecystitis and a burn of the transverse colon have also been observed (11,26).
In our review, attention was drawn to biliary complications. A biliary fistula associated with an abscess occurred in one case and was treated with percutaneous drainage. Also, bile duct strictures were observed in three cases. The clinical relevance of a bile duct stricture is dependent on its location. It may be unsuspected or result in hepatic dysfunction. It was unsuspected in two patients in whom only a peripheral duct was affected, although it led to complete atrophy of the lateral segment of the left lobe in one of them (Fig 12). Two patients presented with obstructive jaundice. Endoscopic retrograde cholangiopancreatography (ERCP) showed a centrally located stricture in one of them and debris within the proximal part of the common bile duct but with no stricture in the other patient. ERCP in these two also showed venous opacification at the periphery of the defect and subsequent leak of contrast medium within the defect (Fig 13).
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Figure 12a. Biliary stricture and parenchymal atrophy in a 71-year-old man with hepatocellular carcinoma. (a) CT scan obtained 2 months after ablation shows complete ablation (arrowheads) in the lateral segment of the left lobe. A subtle dilatation of the biliary ducts is seen centrally (arrow). (b) CT scan obtained 2 years after ablation shows progression of the biliary ductal dilatation with atrophy of the lateral segment of the left lobe (arrow).
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Figure 12b. Biliary stricture and parenchymal atrophy in a 71-year-old man with hepatocellular carcinoma. (a) CT scan obtained 2 months after ablation shows complete ablation (arrowheads) in the lateral segment of the left lobe. A subtle dilatation of the biliary ducts is seen centrally (arrow). (b) CT scan obtained 2 years after ablation shows progression of the biliary ductal dilatation with atrophy of the lateral segment of the left lobe (arrow).
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Figure 13a. Biliary fistula in a 62-year-old man with metastatic colon carcinoma. (a, b) CT scans obtained 3 months after ablation show an ablation defect (arrowheads) in segments V and VI. Dilated bile ducts (arrow in b) abut the defect at a slightly lower level than in a. (c, d) Endoscopic retrograde cholangiopancreatograms show opacified portal vein branches (arrows in c) at the ablation site and leakage of contrast medium into the ablation defect (arrow in d).
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Figure 13b. Biliary fistula in a 62-year-old man with metastatic colon carcinoma. (a, b) CT scans obtained 3 months after ablation show an ablation defect (arrowheads) in segments V and VI. Dilated bile ducts (arrow in b) abut the defect at a slightly lower level than in a. (c, d) Endoscopic retrograde cholangiopancreatograms show opacified portal vein branches (arrows in c) at the ablation site and leakage of contrast medium into the ablation defect (arrow in d).
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Figure 13c. Biliary fistula in a 62-year-old man with metastatic colon carcinoma. (a, b) CT scans obtained 3 months after ablation show an ablation defect (arrowheads) in segments V and VI. Dilated bile ducts (arrow in b) abut the defect at a slightly lower level than in a. (c, d) Endoscopic retrograde cholangiopancreatograms show opacified portal vein branches (arrows in c) at the ablation site and leakage of contrast medium into the ablation defect (arrow in d).
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Figure 13d. Biliary fistula in a 62-year-old man with metastatic colon carcinoma. (a, b) CT scans obtained 3 months after ablation show an ablation defect (arrowheads) in segments V and VI. Dilated bile ducts (arrow in b) abut the defect at a slightly lower level than in a. (c, d) Endoscopic retrograde cholangiopancreatograms show opacified portal vein branches (arrows in c) at the ablation site and leakage of contrast medium into the ablation defect (arrow in d).
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We also observed in two patients development of an arteriovenous fistula at the site of ablation, with a small aneurysm in one of them (Fig 14). Varices acting as collateral vessels for an obstructed hepatic vein were seen in one patient (Fig 15).
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Figure 14a. Arteriovenous fistula in a 42-year-old man with metastatic colon carcinoma. (a) One month after radio-frequency ablation, arterial-dominant-phase CT scan shows parenchymal enhancement consistent with arteriovenous fistula. Within the ablation defect, early opacification of a portal branch (arrow) is adjacent to a small artery (arrowhead). (b) CT scan obtained 3 months after ablation shows that the parenchymal enhancement has not changed but the sizes of the artery and portal vein have increased with development of a pseudoaneurysm (arrowhead).
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Figure 14b. Arteriovenous fistula in a 42-year-old man with metastatic colon carcinoma. (a) One month after radio-frequency ablation, arterial-dominant-phase CT scan shows parenchymal enhancement consistent with arteriovenous fistula. Within the ablation defect, early opacification of a portal branch (arrow) is adjacent to a small artery (arrowhead). (b) CT scan obtained 3 months after ablation shows that the parenchymal enhancement has not changed but the sizes of the artery and portal vein have increased with development of a pseudoaneurysm (arrowhead).
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Figure 15. Varices in a 65-year-old woman with metastatic colon carcinoma. CT scan obtained 3 months after radio-frequency ablation shows a tangle of vessels along the margin of the ablation defect and surface of the liver. These collateral vessels (arrows) drain the territory of the obstructed middle hepatic vein. The varices remained stable over 18 months.
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Clinically relevant complications in patients who underwent treatment at our institution mirror the experience of others with a rate of 2% (24).
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Abstract
LEARNING OBJECTIVES FOR TEST...
