AJR 2005; 184:1096-1102
© American Roentgen Ray Society
Evaluation of Liver Metastases After Radiofrequency Ablation: Utility of 18F-FDG PET and PET/CT
David W. Barker,
Ronald J. Zagoria,
Kathryn A. Morton,
Peter V. Kavanagh and
Perry Shen
Department of Radiology, Wake Forest University, Medical Center Blvd.,
Winston-Salem, NC 27157.
Received May 26, 2004;
accepted after revision September 7, 2004.
Address correspondence to D. W. Barker.
Abstract
OBJECTIVE. Our objective was to review the CT appearance of liver
metastases after radiofrequency ablation and to describe the imaging findings
of and utility of 18F-FDG PET and PET/CT in assessing tumor
recurrence after ablation.
CONCLUSION. 18F-FDG PET and PET/CT can provide added
diagnostic information compared with conventional imaging in patients after
radiofrequency ablation of liver metastases and can be useful in guiding
repeat ablation procedures.
Introduction
Radiofrequency ablation is an increasingly popular technique in the
treatment of patients with unresectable liver tumors. Hepatocellular carcinoma
and metastatic colorectal cancer are the two most common malignancies to
affect the liver. Left untreated, both of these have a very poor prognosis
with a 5-year survival rate of close to 0%. Chemotherapy is rarely curative,
but 5-year survival rates increase to as much as 46% with complete surgical
excision [1]. Unfortunately,
few patients with liver tumors have tumors that are considered resectable at
the time of diagnosis. The median survival rate for such inoperable patients,
specifically those with colorectal metastases, is estimated to be fewer than
12 months [2,
3]. Median survival rates
improve to approximately 36 months after percutaneous radiofrequency ablation
[4]. In addition,
radiofrequency ablation of patients with neuroendocrine metastases can provide
prolonged symptomatic relief
[5].
Pretherapy Assessment
A recent abdominal CT or MRI is required for procedure planning. Pretherapy
PET is also helpful to identify unsuspected intra- or extrahepatic lesions and
to serve as a baseline examination. Initial PET was not routinely performed
with the illustrated cases (Figs.
1A,
1B,
1C,
1D,
1E,
2A,
2B,
2C,
2D,
2E,
2F,
3A,
3B,
3C,
3D,
3E,
4A,
4B,
4C,
4D,
4E,
4F,
4G,
5A,
5B,
5C,
5D,
5E,
5F,
5G,
5H,
6A, and
6B) but is indeed becoming
routine as the utility of PET becomes apparent. Patients with more than five
lesions or with lesions larger than 5 cm are less likely to be curable with
radiofrequency ablation. Lesions adjacent to vital structures may be difficult
or impossible to access percutaneously.
View larger version (128K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1A. —78-year-old man with metastatic pancreatic adenocarcinoma
with initial good result after liver radiofrequency ablation but with evidence
of recurrence on follow-up PET and CT. Unenhanced CT scan shows low-density
lesion in right lobe of liver (arrow), which was new compared with
prior imaging studies and highly suspicious for metastasis.
|
|
View larger version (124K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1B. —78-year-old man with metastatic pancreatic adenocarcinoma
with initial good result after liver radiofrequency ablation but with evidence
of recurrence on follow-up PET and CT. Unenhanced CT scan obtained during
treatment shows radiofrequency ablation probe at lesion site.
|
|
View larger version (141K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1C. —78-year-old man with metastatic pancreatic adenocarcinoma
with initial good result after liver radiofrequency ablation but with evidence
of recurrence on follow-up PET and CT. Immediate post-radiofrequency ablation
enhanced CT scan shows hypovascular ablation defect (white arrow),
adjacent gas, and incidental portal venous gas (black arrows), all
expected findings.
|
|
View larger version (89K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1D. —78-year-old man with metastatic pancreatic adenocarcinoma
with initial good result after liver radiofrequency ablation but with evidence
of recurrence on follow-up PET and CT. 18F-FDG PET scan obtained 2
months after radiofrequency ablation shows focal abnormal uptake
(arrow) along deep aspect of ablation defect consistent with
residual/recurrent tumor.
|
|
View larger version (148K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 1E. —78-year-old man with metastatic pancreatic adenocarcinoma
with initial good result after liver radiofrequency ablation but with evidence
of recurrence on follow-up PET and CT. Concurrent enhanced CT scan shows
corresponding nodular enhancement (arrow) at anteromedial aspect of
ablation defect.
|
|
View larger version (150K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2A. —64-year-old man with metastatic colorectal adenocarcinoma
with successful liver radiofrequency ablation and no evidence of recurrence at
ablation site on follow-up imaging. Enhanced CT scan obtained before
radiofrequency ablation shows hypovascular liver lesion (arrow).
Biopsy performed at time of ablation confirmed adenocarcinoma.
|
|
View larger version (136K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B. —64-year-old man with metastatic colorectal adenocarcinoma
with successful liver radiofrequency ablation and no evidence of recurrence at
ablation site on follow-up imaging. Unenhanced CT scan shows approach with
radiofrequency ablation probe.
|
|
View larger version (155K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2C. —64-year-old man with metastatic colorectal adenocarcinoma
with successful liver radiofrequency ablation and no evidence of recurrence at
ablation site on follow-up imaging. Enhanced CT scan obtained immediately
after radiofrequency ablation shows ablation defect. Note peripheral
enhancement (arrows), which is related to hyperemia and should not be
confused with residual tumor enhancement. Peripheral enhancement gradually
decreases over period of weeks to months.
|
|
View larger version (129K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2D. —64-year-old man with metastatic colorectal adenocarcinoma
with successful liver radiofrequency ablation and no evidence of recurrence at
ablation site on follow-up imaging. Enhanced CT scan obtained 3 months after
radiofrequency ablation shows no evidence of abnormal enhancement and no
increase in lesion size to suggest recurrent tumor.
|
|
View larger version (113K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2E. —64-year-old man with metastatic colorectal adenocarcinoma
with successful liver radiofrequency ablation and no evidence of recurrence at
ablation site on follow-up imaging. Concurrent 18F-FDG PET scan
shows ablation defect (arrow) with no abnormal uptake.
|
|
View larger version (114K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2F. —64-year-old man with metastatic colorectal adenocarcinoma
with successful liver radiofrequency ablation and no evidence of recurrence at
ablation site on follow-up imaging. Enhanced CT scan obtained 9 months after
radiofrequency ablation shows no significant change.
|
|
View larger version (140K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3A. —52-year-old man with metastatic colorectal carcinoma with
initially successful liver radiofrequency ablation but with evidence of
recurrence on follow-up CT and PET. Enhanced CT scan obtained before
radiofrequency ablation shows hypovascular left liver lesion (arrow),
which is enlarged compared with prior imaging studies.
|
|
View larger version (141K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3B. —52-year-old man with metastatic colorectal carcinoma with
initially successful liver radiofrequency ablation but with evidence of
recurrence on follow-up CT and PET. Unenhanced CT scan shows approach with
radiofrequency ablation probe.
|
|
View larger version (139K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3C. —52-year-old man with metastatic colorectal carcinoma with
initially successful liver radiofrequency ablation but with evidence of
recurrence on follow-up CT and PET. Enhanced CT scan obtained immediately
after radiofrequency ablation shows ablation defect with thin rim enhancement
(arrows), again compatible with hyperemia.
|
|
View larger version (141K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3D. —52-year-old man with metastatic colorectal carcinoma with
initially successful liver radiofrequency ablation but with evidence of
recurrence on follow-up CT and PET. Enhanced CT scan obtained 15 months after
radiofrequency ablation shows significant enlargement of left liver lesion
(large arrow), ill-defined margins, and minimal peripheral
enhancement compatible with recurrence. Wedge-shaped peripheral defect
(small arrow) is noted in right lobe of liver. This is site of
metastasis identified during interval surgery and treated with wedge
resection. CT appearance of this latter lesion is believed to represent
postsurgical change.
|
|
View larger version (91K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3E. —52-year-old man with metastatic colorectal carcinoma with
initially successful liver radiofrequency ablation but with evidence of
recurrence on follow-up CT and PET. Concurrent 18F-FDG PET scan
shows focal uptake in both lesions, compatible with recurrence. Note that most
of 18F-FDG uptake in larger lesion (arrow) is along
leftward margin. This information would be helpful in guiding repeat
radiofrequency ablation procedure and is information not provided by CT
scan.
|
|
View larger version (165K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4A. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Coronal reformatted image from
enhanced CT scan obtained 15 months after radiofrequency ablation shows
ablation defect (arrow) but no evidence of enlargement or abnormal
enhancement to suggest tumor recurrence.
|
|
View larger version (114K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4B. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Concurrent coronal
18F-FDG PET image shows focal abnormal uptake (white
arrow) along medial aspect of ablation defect (black arrow)
compatible with recurrence.
|
|
View larger version (177K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4C. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Transaxial CT image (C)
and transaxial PET image (D) from the same studies as (A) and
(B) again show the ablation defect (black arrow, C) and
abnormal uptake on PET (arrows, D).
|
|
View larger version (82K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4D. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Transaxial CT image (C)
and transaxial PET image (D) from the same studies as (A) and
(B) again show the ablation defect (black arrow, C) and
abnormal uptake on PET (arrows, D). Transaxial PET image of
same lesion shows abnormal uptake (arrows).
|
|
View larger version (155K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4E. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Six weeks later, unenhanced CT
scan obtained before repeat radiofrequency ablation shows placement of biopsy
needle, guided by uptake on PET scan. Specimen confirmed adenocarcinoma.
|
|
View larger version (172K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4F. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Unenhanced CT scan shows
initial probe placement for ablation. Probe was then repositioned to adjacent
sites, for total of five ablations, each lasting 10-12 min and each guided by
corresponding PET information.
|
|
View larger version (174K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 4G. —75-year-old man with metastatic colorectal adenocarcinoma
after liver radiofrequency ablation with no evidence of recurrence on CT scan
but with PET scan that reveals recurrent tumor. Enhanced CT scan obtained
immediately after radiofrequency ablation shows adequate ablation defect
(arrows).
|
|
View larger version (75K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5A. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Enhanced CT scan obtained before
radiofrequency ablation shows suspicious hypervascular lesion (arrow)
in dome of liver.
|
|
View larger version (79K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5B. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Concurrent 18F-FDG PET scan
(coronal image) shows corresponding focal increased uptake (arrow)
consistent with malignancy.
|
|
View larger version (95K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5C. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. 18F-FDG PET scan (coronal
image) obtained 4 months after laparoscopic radiofrequency ablation shows
large ablation defect (white arrow) but persistent focal uptake in
liver dome (black arrow).
|
|
View larger version (93K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5D. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Enhanced CT scan obtained 5 months after
radiofrequency ablation shows interval enlargement of enhancing focus
(arrow).
|
|
View larger version (142K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5E. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Unenhanced CT scan shows percutaneous
approach for second radiofrequency ablation procedure.
|
|
View larger version (128K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5F. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Enhanced CT scan performed 1 month after
second radiofrequency ablation procedure shows no evidence of abnormal
enhancement to suggest recurrent tumor. High density in more central aspect of
ablation site is unchanged from prior CT scans and likely represents debris
related to coagulative necrosis.
|
|
View larger version (96K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5G. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Concurrent 18F-FDG PET scan
(coronal image) (G) and transaxial image (arrow, H) of
same lesion show ablation defect (black arrow, G), resolution
of previous metabolically active lesion, but evidence of new focal uptake
(white arrow, G) along superior leftward aspect of ablation
site compatible with recurrent tumor. Again, PET data would be helpful in
targeting any subsequent radiofrequency ablation procedure.
|
|
View larger version (102K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 5H. —60-year-old man with metastatic colorectal adenocarcinoma and
suspicious enhancing lesion in dome of liver treated with two separate
radiofrequency ablation procedures. Concurrent 18F-FDG PET scan
(coronal image) (G) and transaxial image (arrow, H) of
same lesion show ablation defect (black arrow, G), resolution
of previous metabolically active lesion, but evidence of new focal uptake
(white arrow, G) along superior leftward aspect of ablation
site compatible with recurrent tumor. Again, PET data would be helpful in
targeting any subsequent radiofrequency ablation procedure.
|
|
View larger version (124K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6A. —66-year-old woman with metastatic colorectal adenocarcinoma
after multiple liver radiofrequency ablation procedures with
recurrent/residual tumor delineated by PET/CT. Scan from unenhanced CT portion
of examination shows multiple large and small, low- and mixed-density lesions
throughout liver likely representing combination of ablation defects and
recurrent/residual tumor.
|
|
View larger version (104K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 6B. —66-year-old woman with metastatic colorectal adenocarcinoma
after multiple liver radiofrequency ablation procedures with
recurrent/residual tumor delineated by PET/CT. Fused PET/CT image from same
examination shows three foci of increased 18F-FDG uptake, clearly
distinguishing tumor from ablation change and providing precise localization
for radiofrequency ablation planning.
|
|
Technique
Radiofrequency ablation can be performed percutaneously, laparoscopically,
or during open surgery. Percutaneous procedures are typically guided with CT
or sonography. Most radiofrequency ablation probes function in a similar
fashion, with a radiofrequency generator providing current and energy
deposited into tissues through an uninsulated probe tip. Tissue is destroyed
within seconds as temperatures reach 55°C and destroyed immediately at
temperatures greater than 60°C. Larger tumors may require multiple
ablations, which can be performed by redirecting the probe from a single
access site.
Initial Imaging Evaluation
A contrast-enhanced CT scan can be obtained within the first 24 hr after
radiofrequency ablation. This confirms the ablation zone, identifies any
residual tumor enhancement, and provides a baseline for future imaging
studies. Contrast timing is optimized to the portal venous phase except for
cases of hepatocellular carcinoma or hypervascular metastases, in which a
dual-phased (arterial and portal venous) examination is performed. The
ablation site will appear as a hypovascular defect, typically with
well-defined margins. Contrast enhancement is frequently seen surrounding the
defect, more prominently on the arterial than on the portal venous phase. This
rim enhancement is likely related to inflammation and hyperemia of adjacent
liver tissue and does not necessarily represent residual tumor
[6]. Adequate ablation is best
confirmed on the immediate post-ablation CT, irrespective of rim enhancement,
by comparing the size of the distinct hypovascular ablation zone to the size
of the lesion on the preablation CT, preferably including a 5- to 10-mm
margin. For patients undergoing percutaneous CT-guided radiofrequency
ablation, the contrast-enhanced examination can be performed while the patient
is still prepared and sedated, allowing immediate repeat ablation if
necessary.
Follow-Up Imaging Evaluation
Further imaging follow-up is performed weeks to months later to assess
tumor recurrence. CT, MRI, and 18F-FDG PET have all been used in
this regard.
CT scans and MR images should be assessed for regions of abnormal contrast
enhancement. Regarding the more diffuse peripheral enhancement mentioned
previously, it may persist but should decrease over a period of weeks, as
inflammation and hyperemia subside. Increasing enhancement, particularly
irregular or nodular enhancement, should be considered suspicious. With both
techniques, the most obvious sign of recurrence is interval enlargement of the
lesion.
18F-FDG PET is well established in the general evaluation of
colorectal metastases to the liver and is highly sensitive and specific, with
multiple studies showing greater accuracy than CT or MRI
[7]. Extending the use of PET
to assess the same lesions after radiofrequency ablation is therefore logical,
and small studies have shown greater accuracy of PET compared with CT in
evaluating for residual or recurrent tumor
[8,
9].
18F-FDG PET and, in particular, PET/CT also have the added
benefit of precisely localizing the most highly metabolic regions of tumor
recurrence. Lesions that on CT or MRI have no enhancement or diffuse
peripheral enhancement often will have focal uptake on FDG PET. This added
information can be used to direct biopsy if desired or can be used to direct
repeat radiofrequency ablation.
As we stated earlier, radiofrequency ablation of the liver for colorectal
metastases is associated with improved median survival. An uncertainty is the
benefit of repeat radiofrequency ablation in the event of recurrence. Solbiati
et al. [4] analyzed 34 patients
who underwent radiofrequency ablation retreatment of the liver and found a
nonsignificant trend toward further improved survival. Additional larger
studies will be necessary to validate this trend. PET and PET/CT may help to
accomplish this goal.
The studies in Figures 1A,
1B,
1C,
1D,
1E,
2A,
2B,
2C,
2D,
2E,
2F,
3A,
3B,
3C,
3D,
3E,
4A,
4B,
4C,
4D,
4E,
4F,
4G,
5A,
5B,
5C,
5D,
5E,
5F,
5G,
5H,
6A, and
6B review typical findings
with CT and illustrate the added benefit of PET and PET/CT in patients who
have undergone liver tumor radiofrequency ablation.
Conclusion
Radiofrequency ablation improves the survival rates of patients with
unresectable liver metastases. The previously discussed cases review typical
CT findings after liver radiofrequency ablation and illustrate the added
diagnostic information provided by 18F-FDG PET and PET/CT. This
added information will be particularly useful in patients with recurrent tumor
who are considered for repeat radiofrequency ablation treatment.
References
- Harmon K, Ryan J, Biehl T, Lee F. Benefits and safety of hepatic
resection for colorectal metastases. Am J Surg1999; 177:402
-404[Medline]
- Baden H, Anderson B. Survival of patients with untreated liver
metastases from colorectal cancer. Scand J
Gastroenterol 1975;10:221
-223[Medline]
- Wagner JS, Adson MA, Van Heerden JA, Adson MH, Ilstrup DM. The
natural history of hepatic metastases from colorectal cancer. Ann
Surg 1984;199:502
-507[Medline]
- Solbiati L, Livraghi T, Goldberg SN, et al. Percutaneous
radio-frequency ablation of hepatic metastases from colorectal cancer:
long-term results in 117 patients. Radiology2001; 221:159
-166[Abstract/Free Full Text]
- Henn AR, Levine EA, McNulty W, Zagoria RJ. Percutaneous
radiofrequency ablation of hepatic metastases for symptomatic relief of
neuroendocrine syndromes. AJR2003; 181:1005
-1010[Abstract/Free Full Text]
- Limanond P, Zimmerman P, Raman SS, Kadell BM, Lu DS. Interpretation
of CT and MRI after radiofrequency ablation of hepatic malignancies.
AJR 2003;181:1635
-1640[Free Full Text]
- Kinkel K, Lu Y, Both M, Warren RS, Thoeni RF. Detection of hepatic
metastases from cancers of the gastrointestinal tract by using noninvasive
imaging methods (US, CT, MR imaging, PET): a meta-analysis.
Radiology2002; 224:748
-756[Abstract/Free Full Text]
- Anderson GS, Brinkmann F, Soulen MC, Alavi A, Zhuang H. FDG
positron emission tomography in the surveillance of hepatic tumors treated
with radiofrequency ablation. Clin Nucl Med2003; 28:192
-197[Medline]
- Donckier V, Van Laethem JL, Goldman S, et al. [F-18]
fluorodeoxyglucose positron emission tomography as a tool for early
recognition of incomplete tumor destruction after radiofrequency ablation for
liver metastases. J Surg Oncol2003; 84:215
-223[Medline]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
|
|
 
T. M. Blodgett, C. C. Meltzer, and D. W. Townsend
PET/CT: Form and Function
Radiology,
February 1, 2007;
242(2):
360 - 385.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Abstract
Introduction
