DOI: 10.1148/rg.231025055
(Radiographics. 2003;23:107-121.)
© RSNA, 2003
Hepatocellular Carcinoma Treated with Radio-frequency Ablation: Spectrum of Imaging Findings1
Seung Kwon Kim, MD,
Hyo Keun Lim, MD,
Young Han Kim, MD,
Won Jae Lee, MD,
Soon Jin Lee, MD,
Seung Hoon Kim, MD,
Jae Hoon Lim, MD and
Soo Ah Kim, MD
1 From the Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul 135-710, South Korea. Presented as an education exhibit at the 2001 RSNA scientific assembly. Received March 13, 2002; revision requested April 25 and received June 10; accepted June 10. Address correspondence to H.K.L. (e-mail: hklim@smc.samsung.co.kr).
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Abstract
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Contrast material–enhanced Doppler or gray-scale harmonic ultrasonography (US) may help determine the completeness or long-term therapeutic efficacy of radio-frequency (RF) ablation of hepatocellular carcinoma (HCC). Successfully treated HCC is devoid of vascularity at color or power Doppler US. When the tumor is not completely treated, residual viable tumor can be detected. These contrast-enhanced US techniques may also help identify residual tumor when performed during repeat RF ablation, when accurate localization of viable tumor is needed. To date, contrast-enhanced computed tomography (CT) has been the most widely used imaging modality in the evaluation of therapeutic response after RF ablation of HCC. At follow-up CT, successfully ablated lesions appear as low-attenuation areas with no foci of contrast enhancement either within or at the periphery of the treated lesion, whereas any foci of enhancement indicate residual or recurrent tumor. Reactive hyperemia in tissue surrounding the ablated lesion, iatrogenic arterioportal shunting, and small intralesional air pockets are frequently seen at immediate follow-up CT. Gadolinium-enhanced dynamic magnetic resonance imaging is also useful in assessing therapeutic response following RF ablation of HCC, particularly when CT findings are inconclusive. Familiarity with these imaging findings is helpful in this setting.
© RSNA, 2003
Index Terms: Liver neoplasms, 76.323 • Liver neoplasms, CT, 76.1211 • Liver neoplasms, MR, 76.1214 • Liver neoplasms, therapy • Liver neoplasms, US, 76.1298 • Radiofrequency (RF) ablation, 761.1269
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:
- Describe both typical and unusual imaging findings in HCC treated with RF ablation.
- Discuss the role of imaging in the assessment of therapeutic response following RF ablation of HCC.
- Recognize the radiologic manifestations of complete ablation and residual or recurrent tumor after RF ablation of HCC.
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Introduction
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Although surgical resection is the best curative treatment option for hepatocellular carcinoma (HCC), advanced liver cirrhosis or multicentricity makes surgery impossible at the time of diagnosis in a majority of cases (1–2). In the past decade, a variety of minimally invasive techniques have been used as alternatives to hepatic resection in the treatment of small HCCs. These techniques include transcatheter arterial chemoembolization (TACE), local ablation techniques performed with a direct intratumoral injection of compounds such as absolute ethanol and hot saline solution, and thermal ablation techniques such as cryosurgery, microwave ablation, interstitial laser photocoagulation, and radio-frequency (RF) ablation (3–9). Recently, RF ablation has shown itself to be a more promising technique than percutaneous ethanol injection in the treatment of small HCCs. RF ablation has a higher rate of complete necrosis, a fact that allows fewer treatment sessions (9–12).
Precise imaging evaluation is important in determining whether a tumor is completely treated or needs additional treatment. Early detection of residual or locally recurrent tumor after RF ablation of HCC is critical and can facilitate successful retreatment at an early stage. Late diagnosis results in peripheral regrowth and makes retreatment difficult owing to limited access.
RF ablation is performed by placing a needle electrode directly into the tumor with imaging guidance, most often with ultrasonography (US). After successful treatment, the lesion is devoid of vascularity at color or power Doppler US and no longer enhances at contrast material-enhanced computed tomography (CT) or magnetic resonance (MR) imaging. When a tumor has not been completely treated, residual viable tissue manifesting as hypervascular foci can be detected within the lesion at Doppler US, CT, and MR imaging (13–17). In this article, we review the imaging findings in HCC treated with RF ablation and discuss the advantages and pitfalls of each imaging modality in evaluating therapeutic response.
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Ultrasonography
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US or CT is most often used as the primary guidance technique in RF ablation therapy for HCC. Of these modalities, gray-scale US is preferred because it is more widely available, less expensive, and allows real-time monitoring, which facilitates placement of the electrode needle. However, it is of little help in determining the completeness of the procedure or in long-term follow-up of therapeutic efficacy (13,18,19). Postablation gray-scale US cannot help differentiate viable tumor from necrotic tissue because of variable echogenicity (Fig 1) and because postablation US findings do not correlate well with the overall shape and volume of the necrosis (20,21).
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Figure 1. Variable echogenicity at US performed in a 45-year-old man who had undergone RF ablation for HCC. Oblique gray-scale US image of the right hepatic lobe obtained 18 hours after treatment shows a large mass with mixed echogenicity (arrows). Variable echogenicity of a mass following treatment makes it difficult to differentiate residual tumor from the necrotic portion.
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Although several reports have shown that color Doppler US is somewhat useful in the assessment of therapeutic efficacy after local ablation therapy for HCC (13,14,22), neither color nor power Doppler US has proved entirely satisfactory because of low sensitivity to microvasculature within residual viable tumor (16,18,23–25).
Recently, blood pool microbubble contrast agents have become available for use with Doppler US. A microbubble contrast agent such as SH U 508A (Levovist; Schering, Berlin, Germany) amplifies the Doppler signal by allowing increased signal reflection from intravascular microbubbles. Microbubble contrast material–enhanced power Doppler US has been reported to depict tumor vascularity in HCC better than unenhanced power Doppler US (26). Several reports have suggested that contrast-enhanced color and power Doppler US can be useful in detecting residual or recurrent tumors after RF ablation of HCC (Figs 2, 3) (16,24,27). Solbiati et al (24) also reported that contrast-enhanced US can help detect residual tumor after RF ablation therapy for hepatic metastases.
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Figure 2a. Successful RF ablation in a 48-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows a 1.7-cm HCC with partial contrast enhancement in segment VI of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 hour after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis. (c) Contrast-enhanced power Doppler US image shows no flow signals within the ablated area, a finding that is consistent with complete tumor necrosis.
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Figure 2b. Successful RF ablation in a 48-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows a 1.7-cm HCC with partial contrast enhancement in segment VI of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 hour after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis. (c) Contrast-enhanced power Doppler US image shows no flow signals within the ablated area, a finding that is consistent with complete tumor necrosis.
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Figure 2c. Successful RF ablation in a 48-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows a 1.7-cm HCC with partial contrast enhancement in segment VI of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 hour after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis. (c) Contrast-enhanced power Doppler US image shows no flow signals within the ablated area, a finding that is consistent with complete tumor necrosis.
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Figure 3a. Residual tumor in a 72-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC in segment VI of the liver (arrows). (b) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 2 hours after RF ablation, most of the ablated area (arrows) has low attenuation, but a focal crescentic enhancing portion (arrowheads) is noted at the medial aspect of the ablated area. Nodular enhancement representing residual viable tumor is also noted. (c) Contrast-enhanced power Doppler US image obtained 18 hours after RF ablation shows focal flow signals (arrowheads) that represent residual tumor vessels within the ablated area (arrows). The residual tumor was treated with repeat RF ablation later the same day.
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Figure 3b. Residual tumor in a 72-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC in segment VI of the liver (arrows). (b) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 2 hours after RF ablation, most of the ablated area (arrows) has low attenuation, but a focal crescentic enhancing portion (arrowheads) is noted at the medial aspect of the ablated area. Nodular enhancement representing residual viable tumor is also noted. (c) Contrast-enhanced power Doppler US image obtained 18 hours after RF ablation shows focal flow signals (arrowheads) that represent residual tumor vessels within the ablated area (arrows). The residual tumor was treated with repeat RF ablation later the same day.
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Figure 3c. Residual tumor in a 72-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC in segment VI of the liver (arrows). (b) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 2 hours after RF ablation, most of the ablated area (arrows) has low attenuation, but a focal crescentic enhancing portion (arrowheads) is noted at the medial aspect of the ablated area. Nodular enhancement representing residual viable tumor is also noted. (c) Contrast-enhanced power Doppler US image obtained 18 hours after RF ablation shows focal flow signals (arrowheads) that represent residual tumor vessels within the ablated area (arrows). The residual tumor was treated with repeat RF ablation later the same day.
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According to a recent preliminary report, contrast-enhanced power Doppler US can be used as an alternative to immediate follow-up CT for early assessment of the therapeutic efficacy of RF ablation of HCC (16). Another advantage of contrast-enhanced power Doppler US over CT and MR imaging is that it can directly show persistent fine vascular flow signals within the tumor during a period of effective contrast enhancement that lasts for more than 10 minutes. Consequently, contrast-enhanced Doppler or gray-scale harmonic US could be helpful in detecting residual or recurrent tumor after RF ablation of HCC. These modalities may also be helpful in identifying residual tumor when performed during repeat ablation, when accurate localization of viable tumor is needed. This real-time confirmation of the accurate localization of viable tumor and of correct placement of the electrode within the tumor cannot be expected at CT and may reduce the number of treatment sessions without further use of contrast-enhanced CT or MR imaging (16,24,27). Furthermore, contrast-enhanced CT is less than ideal because errors in contrast bolus timing cannot always be corrected immediately with repeat scanning due to the risk of toxicity. However, real-time US and the ability to administer repeated doses of US contrast material may, in some cases, allow better detection of residual tumor.
More recently, contrast-enhanced gray-scale harmonic US has been developed for the evaluation of therapeutic response to RF ablation therapy (28). This technique allows detection of residual tumor after ablation without the blooming and motion artifacts seen at contrast-enhanced color or power Doppler US (Figs 4, 5). However, the results obtained with this new technique are preliminary, and prospective studies with a large population of patients are needed for definitive assessment of its value.
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Figure 4a. Successful RF ablation in a 63-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.3-cm HCC in the subcapsular portion of segment VII of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique before RF ablation shows the tumor with homogeneous enhancement (arrows). Note also the feeding hepatic artery (arrowheads). (c) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows that the ablated lesion has become avascular (arrows). (d) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 4b. Successful RF ablation in a 63-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.3-cm HCC in the subcapsular portion of segment VII of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique before RF ablation shows the tumor with homogeneous enhancement (arrows). Note also the feeding hepatic artery (arrowheads). (c) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows that the ablated lesion has become avascular (arrows). (d) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 4c. Successful RF ablation in a 63-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.3-cm HCC in the subcapsular portion of segment VII of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique before RF ablation shows the tumor with homogeneous enhancement (arrows). Note also the feeding hepatic artery (arrowheads). (c) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows that the ablated lesion has become avascular (arrows). (d) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 4d. Successful RF ablation in a 63-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.3-cm HCC in the subcapsular portion of segment VII of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique before RF ablation shows the tumor with homogeneous enhancement (arrows). Note also the feeding hepatic artery (arrowheads). (c) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows that the ablated lesion has become avascular (arrows). (d) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 5a. Residual tumor in a 78-year-old woman with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.1-cm HCC in segment III of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows nodular enhancement (arrowheads) that represents untreated residual tumor at the posterior aspect of the ablated area (arrows). (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation also demonstrates nodular enhancement (arrowheads) at the posterior aspect of the ablated area (arrows). The residual tumor was treated with repeat RF ablation.
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Figure 5b. Residual tumor in a 78-year-old woman with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.1-cm HCC in segment III of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows nodular enhancement (arrowheads) that represents untreated residual tumor at the posterior aspect of the ablated area (arrows). (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation also demonstrates nodular enhancement (arrowheads) at the posterior aspect of the ablated area (arrows). The residual tumor was treated with repeat RF ablation.
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Figure 5c. Residual tumor in a 78-year-old woman with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.1-cm HCC in segment III of the liver (arrows). (b) Contrast-enhanced gray-scale US image obtained with a coded harmonic angiographic technique 19 hours after RF ablation shows nodular enhancement (arrowheads) that represents untreated residual tumor at the posterior aspect of the ablated area (arrows). (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation also demonstrates nodular enhancement (arrowheads) at the posterior aspect of the ablated area (arrows). The residual tumor was treated with repeat RF ablation.
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At our institution, immediate therapeutic response is evaluated with contrast-enhanced Doppler or gray-scale harmonic US within 24 hours after RF ablation of HCC. When residual tumor is found, repeat RF ablation is performed under contrast-enhanced US guidance during the same admission period. In addition, contrast-enhanced US may be performed if the presence of residual or recurrent tumor is suspected at follow-up CT.
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Computed Tomography
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Contrast-enhanced CT has been the most widely used imaging modality (including at our institution) in the evaluation of therapeutic response to RF ablation of HCC (19,29–33). Although the optimal period for follow-up CT has yet to be determined, in our experience, a time interval of 1–3 months has proved to be acceptable (29). Our follow-up CT protocol is as follows: Initial follow-up CT is performed 1 month after the completion of RF ablation to determine the possible presence of residual tumor and postprocedural complications. Repeat follow-up CT is performed every 3 months thereafter to determine the possible presence of marginal or remote recurrence or of new primary HCC (29). Occasionally, we perform CT immediately after treatment to assess for completeness of the ablation and for acute complications when contrast-enhanced US does not sufficiently demonstrate them or is not performed. At our institution, all follow-up CT is performed on a helical scanner with 5-mm collimation and a 5-mm/sec table speed. Three-phase helical CT scans are obtained 30 seconds, 70 seconds, and 3 minutes after the start of intravenous bolus injection of 120 mL of nonionic contrast material at a rate of 3 mL/sec.
At follow-up CT, all completely ablated lesions appear as a hypoattenuating area with no foci of contrast enhancement either within the lesion or at its periphery (Fig 6). Moreover, for RF ablation to be complete, the entire tumor as well as a peripheral safety margin of 0.5–1 cm of normal hepatic tissue must be ablated (Fig 7). In all cases in our study, 1-month follow-up CT showed the ablated lesion to be larger than the preablation tumor (30). Therefore, we believe that an ablated lesion that is not larger than the preablation tumor should be followed up closely. Long-term follow-up CT shows a gradual decrease in the volume of the ablated lesion (30). In our experience, this volume change does not always indicate successful ablation, but is thought to represent only residual necrotic or fibrotic tissue that is present during the absorption process. Nonenhancing ablated lesions are often encountered, the size of which remains unchanged over several follow-up CT scans. In such cases, no additional imaging is required to confirm the presence of residual or recurrent tumor until findings appear that are highly suggestive of marginal recurrence (eg, focal enhancement, increased size). When findings at short-term follow-up CT are inconclusive and the suspected lesion is small, follow-up at 1- to 3-month intervals is acceptable before performing an invasive diagnostic procedure such as percutaneous biopsy or retreatment (29). In our study, eight of 38 ablated HCCs without foci of contrast enhancement at 1-month follow-up CT revealed peripheral tumor recurrence on subsequent follow-up CT scans obtained 4-13 months after treatment (30). Besides this marginal recurrence, remote recurrence or new primary HCC may develop in the cirrhotic liver. Thus, follow-up CT at 3-month intervals is highly recommended.
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Figure 6a. Successful RF ablation in a 70-year-old woman with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows a partially enhancing 3.1-cm HCC in segment VIII of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase CT scan obtained immediately after RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete necrosis of the tumor. Note also the hyperemia surrounding the tumor (arrowheads). (c) On an axial follow-up CT scan obtained 17 months later, the ablated lesion (arrows) remains unenhanced and shows an interval decrease in size.
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Figure 6b. Successful RF ablation in a 70-year-old woman with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows a partially enhancing 3.1-cm HCC in segment VIII of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase CT scan obtained immediately after RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete necrosis of the tumor. Note also the hyperemia surrounding the tumor (arrowheads). (c) On an axial follow-up CT scan obtained 17 months later, the ablated lesion (arrows) remains unenhanced and shows an interval decrease in size.
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Figure 6c. Successful RF ablation in a 70-year-old woman with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows a partially enhancing 3.1-cm HCC in segment VIII of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase CT scan obtained immediately after RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete necrosis of the tumor. Note also the hyperemia surrounding the tumor (arrowheads). (c) On an axial follow-up CT scan obtained 17 months later, the ablated lesion (arrows) remains unenhanced and shows an interval decrease in size.
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Figure 7a. Successful RF ablation in a 64-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 1.5-cm HCC in segment V of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis. Note that the ablated lesion is much larger than the enhancing tumor (cf a), which indicates that there is a sufficient safety margin.
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Figure 7b. Successful RF ablation in a 64-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 1.5-cm HCC in segment V of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis. Note that the ablated lesion is much larger than the enhancing tumor (cf a), which indicates that there is a sufficient safety margin.
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Any focal enhancement in the treated lesion should be considered indicative of residual or recurrent tumor (Figs 8, 9). However, the absence of contrast enhancement within the ablated lesion at either immediate or short-term follow-up CT performed up to 3 months after treatment does not always indicate successful treatment; later follow-up may demonstrate tumor regrowth at the periphery of the ablated lesion in some cases (Fig 9). On the other hand, not all peripherally enhancing lesions seen at short-term follow-up CT performed within 1 month after treatment should be regarded as residual viable tumor. Reactive hyperemia in tissue surrounding the ablated lesion represents inflammatory reaction to the thermal injury and frequently occurs during this period. Peripheral rim enhancement resulting from reactive hyperemia is usually uniform in thickness and envelops the ablated lesion, whereas residual tumor demonstrates focal and irregular peripheral enhancement. In addition, peripheral rim enhancement representing reactive hyperemia is high- or isoattenuating during the portal venous and equilibrium phases. Such reactive hyperemia in tissue surrounding the ablated lesion may make accurate assessment of therapeutic response difficult (Fig 10). Whether ablation was successful is usually determined on the basis of CT findings obtained 1 month after the procedure. In our experience, reactive hyperemia has usually resolved by this time (30). Nontumorous nodular or wedge-shaped enhancement can also occur at the periphery of the ablated lesion owing to iatrogenic arterioportal shunting (Fig 11). It is well known that percutaneous needle biopsy and percutaneous ethanol injection can produce arterioportal shunting along the needle track (34,35). It is usually easy to differentiate residual tumor from arterioportal shunting at multiphasic helical CT because residual tumor usually has high attenuation during the hepatic arterial phase and low attenuation during the portal venous and equilibrium phases.
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Figure 8a. Residual tumor in a 59-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 2-cm HCC in segment VII of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows nodular enhancement (arrowheads) at the posterior aspect of the ablated lesion (arrows). The enhancing nodule was thought to represent residual viable tumor and was treated with repeat RF ablation. (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after repeat RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete necrosis of the tumor.
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Figure 8b. Residual tumor in a 59-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 2-cm HCC in segment VII of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows nodular enhancement (arrowheads) at the posterior aspect of the ablated lesion (arrows). The enhancing nodule was thought to represent residual viable tumor and was treated with repeat RF ablation. (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after repeat RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete necrosis of the tumor.
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Figure 8c. Residual tumor in a 59-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 2-cm HCC in segment VII of the liver (arrows). (b) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation shows nodular enhancement (arrowheads) at the posterior aspect of the ablated lesion (arrows). The enhancing nodule was thought to represent residual viable tumor and was treated with repeat RF ablation. (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after repeat RF ablation shows an unenhanced round ablated area with low attenuation (arrows), a finding that suggests complete necrosis of the tumor.
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Figure 9a. Residual tumor in a 49-year-old man with a 3-cm HCC in segment VIII of the liver. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 4 months after RF ablation shows nodular enhancement (arrowheads) at the lateral aspect of the ablated lesion (arrows). (b) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 6 months after RF ablation, the enhancing nodule (arrowheads) demonstrates an interval increase in size (cf a). The nodule was thought to represent residual viable tumor and was treated with repeat RF ablation. Arrows indicate the ablated lesion. (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 3 months after repeat RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 9b. Residual tumor in a 49-year-old man with a 3-cm HCC in segment VIII of the liver. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 4 months after RF ablation shows nodular enhancement (arrowheads) at the lateral aspect of the ablated lesion (arrows). (b) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 6 months after RF ablation, the enhancing nodule (arrowheads) demonstrates an interval increase in size (cf a). The nodule was thought to represent residual viable tumor and was treated with repeat RF ablation. Arrows indicate the ablated lesion. (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 3 months after repeat RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 9c. Residual tumor in a 49-year-old man with a 3-cm HCC in segment VIII of the liver. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 4 months after RF ablation shows nodular enhancement (arrowheads) at the lateral aspect of the ablated lesion (arrows). (b) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 6 months after RF ablation, the enhancing nodule (arrowheads) demonstrates an interval increase in size (cf a). The nodule was thought to represent residual viable tumor and was treated with repeat RF ablation. Arrows indicate the ablated lesion. (c) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 3 months after repeat RF ablation shows an unenhanced oval ablated area with low attenuation (arrows), a finding that suggests complete tumor necrosis.
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Figure 10a. Reactive hyperemia in a 76-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC with central uptake of iodized oil (Lipiodol; Guerbet, Roissy, France) in segment VIII of the liver (arrows). (b, c) Axial contrast-enhanced hepatic arterial phase (b) and portal venous phase (c) helical CT scans obtained 20 minutes after RF ablation demonstrate uniform rim enhancement (arrows) surrounding the ablated lesion. (d) On an axial equilibrium phase helical CT scan, the rim enhancement is isoattenuating (arrows). (e) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation, the rim enhancement is no longer seen, a finding that helps confirm the diagnosis of reactive hyperemia.
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Figure 10b. Reactive hyperemia in a 76-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC with central uptake of iodized oil (Lipiodol; Guerbet, Roissy, France) in segment VIII of the liver (arrows). (b, c) Axial contrast-enhanced hepatic arterial phase (b) and portal venous phase (c) helical CT scans obtained 20 minutes after RF ablation demonstrate uniform rim enhancement (arrows) surrounding the ablated lesion. (d) On an axial equilibrium phase helical CT scan, the rim enhancement is isoattenuating (arrows). (e) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation, the rim enhancement is no longer seen, a finding that helps confirm the diagnosis of reactive hyperemia.
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Figure 10c. Reactive hyperemia in a 76-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC with central uptake of iodized oil (Lipiodol; Guerbet, Roissy, France) in segment VIII of the liver (arrows). (b, c) Axial contrast-enhanced hepatic arterial phase (b) and portal venous phase (c) helical CT scans obtained 20 minutes after RF ablation demonstrate uniform rim enhancement (arrows) surrounding the ablated lesion. (d) On an axial equilibrium phase helical CT scan, the rim enhancement is isoattenuating (arrows). (e) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation, the rim enhancement is no longer seen, a finding that helps confirm the diagnosis of reactive hyperemia.
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Figure 10d. Reactive hyperemia in a 76-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC with central uptake of iodized oil (Lipiodol; Guerbet, Roissy, France) in segment VIII of the liver (arrows). (b, c) Axial contrast-enhanced hepatic arterial phase (b) and portal venous phase (c) helical CT scans obtained 20 minutes after RF ablation demonstrate uniform rim enhancement (arrows) surrounding the ablated lesion. (d) On an axial equilibrium phase helical CT scan, the rim enhancement is isoattenuating (arrows). (e) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation, the rim enhancement is no longer seen, a finding that helps confirm the diagnosis of reactive hyperemia.
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Figure 10e. Reactive hyperemia in a 76-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained before RF ablation shows an enhancing 3.5-cm HCC with central uptake of iodized oil (Lipiodol; Guerbet, Roissy, France) in segment VIII of the liver (arrows). (b, c) Axial contrast-enhanced hepatic arterial phase (b) and portal venous phase (c) helical CT scans obtained 20 minutes after RF ablation demonstrate uniform rim enhancement (arrows) surrounding the ablated lesion. (d) On an axial equilibrium phase helical CT scan, the rim enhancement is isoattenuating (arrows). (e) On an axial contrast-enhanced hepatic arterial phase helical CT scan obtained 1 month after RF ablation, the rim enhancement is no longer seen, a finding that helps confirm the diagnosis of reactive hyperemia.
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Figure 11a. Iatrogenic arteriovenous shunting in a 36-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 15 minutes after RF ablation shows two unenhanced oval ablated areas with low attenuation (arrows). (b) Axial contrast-enhanced helical CT scan obtained caudad to a shows a wedge-shaped area of enhancement (arrows) that represents iatrogenic arteriovenous shunting at the posterolateral aspect of the ablated lesion. Note the early visualization of the portal vein branch (arrowheads).
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Figure 11b. Iatrogenic arteriovenous shunting in a 36-year-old man with HCC. (a) Axial contrast-enhanced hepatic arterial phase helical CT scan obtained 15 minutes after RF ablation shows two unenhanced oval ablated areas with low attenuation (arrows). (b) Axial contrast-enhanced helical CT scan obtained caudad to a shows a wedge-shaped area of enhancement (arrows) that represents iatrogenic arteriovenous shunting at the posterolateral aspect of the ablated lesion. Note the early visualization of the portal vein branch (arrowheads).
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Air pockets are frequently seen within the ablated lesion at immediate follow-up CT (30). They are usually small in size and number and have usually disappeared by 1-month follow-up CT (Fig 12). They are thought to be generated as a result of tissue necrosis (frequently seen after TACE) or introduced along the insertion path of the needle (31,36). In a study by Mitsuzaki et al (31), four of 14 lesions that contained air pockets after microwave coagulation therapy proved to have hepatic abscess. The affected patients had high fever and pain that persisted for more than 2 weeks. The hepatic abscesses that developed within the ablated lesion in four patients in our study were suspected when fever and abdominal pain developed 2–4 days after RF ablation. All of these patients had extensive air pockets with or without air-fluid levels within the ablated lesion at immediate follow-up CT. However, we believe that small air pockets seen at immediate follow-up CT are of little help in detecting hepatic abscess. Thus, close monitoring of clinical signs and symptoms (eg, fever, chill, abdominal pain, and so on) is mandatory for several days, even after the patient has been discharged from the hospital.
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Figure 12a. Air formation in a 55-year-old man with HCC. (a) Axial contrast-enhanced helical CT scan obtained 15 minutes after RF ablation shows an ablated lesion (arrows) that contains small air pockets (arrowheads). (b) Axial follow-up helical CT scan shows resolution of the air pockets.
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Figure 12b. Air formation in a 55-year-old man with HCC. (a) Axial contrast-enhanced helical CT scan obtained 15 minutes after RF ablation shows an ablated lesion (arrows) that contains small air pockets (arrowheads). (b) Axial follow-up helical CT scan shows resolution of the air pockets.
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At our institution, the serum 
-fetoprotein level is measured and CT is performed every 3 months in patients with HCC treated with RF ablation. An interval increase in the level of this tumor marker is occasionally helpful in assessing subtle changes at CT that suggest marginal recurrence. In such cases, further diagnostic procedures should be performed to confirm the presence of marginal recurrence.
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MR Imaging
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MR imaging also plays an important role in evaluating therapeutic response after RF ablation of HCC. At our institution, MR imaging protocol includes both unenhanced T1- and T2-weighted imaging and gadolinium-enhanced T1-weighted dynamic imaging. Unenhanced MR imaging is known to be less reliable than either contrast-enhanced CT (37) or contrast-enhanced MR imaging (17,38,39) in detecting residual tumor after local ablation therapy. Unenhanced T1- and T2-weighted MR imaging demonstrates markedly heterogeneous signal intensity within the ablated lesion. This variability in signal intensity is most likely caused by an uneven evolution of coagulation necrosis and the host response to thermal injury over time (40).
Gadolinium-enhanced dynamic MR imaging is known to be a useful diagnostic method for evaluating therapeutic response after RF ablation of HCC (17). As at CT, the presence or absence of contrast enhancement in the treated lesion is instructive. A tumor that has been completely treated no longer enhances on gadolinium-enhanced dynamic MR images (Fig 13). When a tumor is not completely treated, residual or recurrent tumor is usually seen as focal and nodular enhancement at the margin of the ablated lesion (Fig 14). However, contrast enhancement does not always correspond to residual tumor discovered at histologic examination of specimens obtained at fine-needle aspiration biopsy or surgical resection. Inflammatory reaction in tissue surrounding the ablated lesion and microscopic arteriovenous shunting can mimic the signal-intensity features of residual tumor (17,41).
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Figure 13a. Successful RF ablation in a 49-year-old man with HCC. (a) Axial spin-echo T1-weighted MR image obtained 1 month after RF ablation shows an oval ablated area (arrows) that is isointense relative to the surrounding liver parenchyma. (b) Axial spin-echo T2-weighted MR image again shows the oval ablated area (arrows) as isointense relative to the surrounding liver parenchyma. Note the high-signal-intensity rim, a finding that represents reactive change. (c) Axial gradient-echo T1-weighted MR image obtained immediately after the administration of gadolinium chelates shows an unenhanced oval ablated area (arrows) that is isointense relative to the surrounding liver parenchyma, a finding that suggests complete tumor necrosis.
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Figure 13b. Successful RF ablation in a 49-year-old man with HCC. (a) Axial spin-echo T1-weighted MR image obtained 1 month after RF ablation shows an oval ablated area (arrows) that is isointense relative to the surrounding liver parenchyma. (b) Axial spin-echo T2-weighted MR image again shows the oval ablated area (arrows) as isointense relative to the surrounding liver parenchyma. Note the high-signal-intensity rim, a finding that represents reactive change. (c) Axial gradient-echo T1-weighted MR image obtained immediately after the administration of gadolinium chelates shows an unenhanced oval ablated area (arrows) that is isointense relative to the surrounding liver parenchyma, a finding that suggests complete tumor necrosis.
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Figure 13c. Successful RF ablation in a 49-year-old man with HCC. (a) Axial spin-echo T1-weighted MR image obtained 1 month after RF ablation shows an oval ablated area (arrows) that is isointense relative to the surrounding liver parenchyma. (b) Axial spin-echo T2-weighted MR image again shows the oval ablated area (arrows) as isointense relative to the surrounding liver parenchyma. Note the high-signal-intensity rim, a finding that represents reactive change. (c) Axial gradient-echo T1-weighted MR image obtained immediately after the administration of gadolinium chelates shows an unenhanced oval ablated area (arrows) that is isointense relative to the surrounding liver parenchyma, a finding that suggests complete tumor necrosis.
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Figure 14a. Marginal recurrent tumor in a 49-year-old man with HCC. (a) Axial spin-echo T1-weighted MR image obtained 7 months after RF ablation shows an oval ablated area with slightly increased signal intensity (arrows). (b) Axial spin-echo T2-weighted MR image shows a small nodular lesion with high signal intensity (arrowheads) at the anterior aspect of the low-signal-intensity ablated lesion (arrows). (c) Axial gradient-echo T1-weighted MR image obtained immediately after the administration of gadolinium chelates shows a small enhancing nodule (arrowheads) that represents marginal recurrent tumor at the anterior aspect of the ablated lesion (arrows). The recurrent tumor was treated with repeat RF ablation.
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Figure 14b. Marginal recurrent tumor in a 49-year-old man with HCC. (a) Axial spin-echo T1-weighted MR image obtained 7 months after RF ablation shows an oval ablated area with slightly increased signal intensity (arrows). (b) Axial spin-echo T2-weighted MR image shows a small nodular lesion with high signal intensity (arrowheads) at the anterior aspect of the low-signal-intensity ablated lesion (arrows). (c) Axial gradient-echo T1-weighted MR image obtained immediately after the administration of gadolinium chelates shows a small enhancing nodule (arrowheads) that represents marginal recurrent tumor at the anterior aspect of the ablated lesion (arrows). The recurrent tumor was treated with repeat RF ablation.
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Figure 14c. Marginal recurrent tumor in a 49-year-old man with HCC. (a) Axial spin-echo T1-weighted MR image obtained 7 months after RF ablation shows an oval ablated area with slightly increased signal intensity (arrows). (b) Axial spin-echo T2-weighted MR image shows a small nodular lesion with high signal intensity (arrowheads) at the anterior aspect of the low-signal-intensity ablated lesion (arrows). (c) Axial gradient-echo T1-weighted MR image obtained immediately after the administration of gadolinium chelates shows a small enhancing nodule (arrowheads) that represents marginal recurrent tumor at the anterior aspect of the ablated lesion (arrows). The recurrent tumor was treated with repeat RF ablation.
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A previous study of the diagnostic efficacy of MR imaging showed that findings on unenhanced and gadolinium-enhanced dynamic MR images correlated well with those on contrast-enhanced CT scans obtained to assess for complete or partial tumor necrosis, with a correspondence rate of 86% (17). Moreover, hypointensity on T2-weighted MR images and loss of enhancement on dynamic MR images indicated completely necrotic lesions in all cases. Another recent study suggested that MR imaging may have an advantage over CT in the early detection of local regrowth of hepatic tumors after RF ablation due to the high sensitivity of T2-weighted imaging (42).
We agree that the findings described previously indicate that contrast-enhanced MR imaging has increased sensitivity for the detection of either residual or recurrent tumor or nontumorous pseudolesion (17,42). At our institution, MR imaging is selectively used in most cases as a problem-solving modality when a discrepancy exists between clinical results and CT findings or when an equivocal lesion is found at CT as expected (43).
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Complications
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The reported complication rate for RF ablation is low and indicates that this is a relatively safe procedure. Complications relevant to the radiologist include (a) bleeding, (b) injury to blood vessels, bile ducts, the diaphragm, or abdominal organs, and (c) infection. In a multicenter study conducted by Livraghi et al (44), two deaths (0.11% of cases) and 27 major complications (1.52%) occurred. Major complications included peritoneal hemorrhage, hepatic abscess (Fig 15), perforation of intestinal loops adjacent to the lesion, tumor seeding along the needle track (Fig 16), biloma (Fig 17), grounding pad burn, hemothorax, and hepatic infarction, among others.
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Figure 15a. Hepatic abscess in a 69-year-old man with HCC. (a) Axial contrast-enhanced helical CT scan obtained 4 days after RF ablation shows an ablated lesion with an oval, mottled air-containing abscess cavity (arrows). The abscess cavity was treated with percutaneous catheter drainage and antibiotics. (b) Axial follow-up helical CT scan obtained 12 months later shows complete resolution of the abscess cavity.
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Abstract
LEARNING OBJECTIVES FOR TEST...
