1. Intra-Procedural Contrast-Enhanced CT for
Percutaneous Ablation of Liver Lesions:
Utility and Treatment Implications
Melissa Price, M.D.¹
Jonathan K. Park, M.D.¹
Aram J. Lee, M.D.¹
Justin P. McWilliams, M.D.¹
¹UCLA Department of Radiological Sciences
Los Angeles, California
3. Objectives
• At our institution, on-table contrast-enhanced CT is
performed as the final step of each percutaneous liver
ablation procedure, and images are reviewed by the
interventionalist prior to concluding the procedure.
• The exhibit will review our experience incorporating this
imaging into our standard ablation procedure algorithm both
for intra-procedural planning and post-procedural
management and treatment.
4. Content Organization
• I. Description of the technique used for on-table contrast-
enhanced CT.
• II. Pictorial review of the expected baseline appearance of
hepatic lesions on post-contrast CT, which is usually
performed immediately post-ablation.
• III. Review cases in which intra-procedural CT directed further
on-table management.
• IV. Provide examples of complications identified on intra-
procedural CT that guided management, including
angiographic intervention for hemorrhage.
5. Introduction
• CT is commonly performed following ablation to
determine whether ablation is complete and to screen
for early recurrences that may benefit from re-ablation
– This is performed at many institutions prior to discharge or at 1-
month follow-up.
– 235 cases of percutaneous liver RFA performed at our institution
over an 18 month period were reviewed.
– Contrast-enhanced CT was performed “on the table” as part of
the procedure in 217 of these cases, usually immediately
following the ablation.
1. Choi H, et al. Radiographics. 2001 Oct;21 Spec No:S41-54.
6. Introduction 2
• Contrast-enhanced CT is performed while the patient is
still on the table as the final step of each liver RFA (unless
contraindicated) at our institution in order to:
– Assess adequacy of ablation
– Detect previously unnoticed lesions that may be immediately ablated
– Detect immediate complications that may dictate further
management
1. Choi H, et al. Radiographics. 2001 Oct;21 Spec No:S41-54.
7. Part I. Technique
• Post-procedure on-table contrast-enhanced reduced dose CT is typically
performed with 70-90 cc of Visipaque contrast injected intravenously at a rate
of 3 cc/sec
• Images are acquired in arterial and portal venous phases
• This may be performed with the needles still in treatment position, with the
needles partially withdrawn, or with the needles completely removed
– Leaving needles in position allows easier re-direction of needles in case residual tumor is
detected, but some beam-hardening artifact may make residual tumor harder to detect
– Removing the needles entirely allows for immediate detection of bleeding, should it
occur, but requires re-insertion of the needles should residual tumor be detected
– This decision is made on a patient-to-patient basis depending on level of concern
• In some cases, post-contrast CT is deferred due to patient allergy or impaired
renal function
8. Part II. Expected CT Appearance of
Hepatic Lesions Post-RFA
• The appearance of the ablated zone may vary depending on
presence of residual tumor and time elapsed from ablation
• Ideally, the tumor should be completely ablated with an ablative
margin thickness of at least 0.5 cm
2. Park MH, et al. Radiographics. 2008 Apr;28(2):279-90.
9. CT Appearance 2
• Pattern I: Ablation zone appears as non-enhancing area of low
attenuation, representing coagulation necrosis. This is the
most common pattern.
2. Park MH, et al. Radiographics. 2008 Apr;28(2):279-90.
10. CT Appearance 3
• Low attenuation area should completely cover margin of
entire index tumor and ablative margin (defined as ablated
hepatic parenchyma around index tumor)
HCC Ablation zone covers
index tumor (black filled
RFA white circle) and ablative
margin (black ring around
white circle)
Metastasis
2. Park MH, et al. Radiographics. 2008 Apr;28(2):279-90.
11. CT Appearance 4
• Pattern II: Uniform peripheral rim of enhancement around the
ablation zone on arterial or portal venous phase
– Thought to indicate benign physiologic response to thermal injury
– Often disappears over time: one study reported this initial finding in
79% of cases and found that it usually disappeared by 1 month.
2. Park MH, et al. Radiographics. 2008 Apr;28(2):279-90.
3. Lim HK, et al. Radiology. 2001 Nov;221(2):447-54.
12. CT Appearance 5
• Pattern III: Zone of ablation contains a central area of high
attenuation along electrode needle tract
– Area of increased attenuation thought to represent greater cellular
disruption
– The high attenuation usually disappears by next follow-up CT
4. Rhim H, et al. Radiographics. 2003 Jan-Feb;23(1):123-34
13. Part III. Intra-procedural CT Directing
Further On-table Management
• Intra-procedural contrast-enhanced CT can detect:
– Additional lesions not noticed or demonstrated on prior imaging
– Inadequate zone of ablation
• These scenarios may be managed by immediate further
ablation or attention on future treatment sessions
14. On-table Management 2
• Additional lesions not noticed or demonstrated on prior
imaging can be ablated at the same session
However, previously unnoticed
Case 1: On-table contrast-enhanced
enhancing tumor was noted anterior
CT demonstrates adequate ablation
to the gallbladder; this was ablated
zone in segment VII
immediately
15. On-table Management 3
• Additional lesions not noticed or demonstrated on prior
imaging can be ablated during the same session
Case 2: Post-RFA arterial phase However, hypervascular nodule was
scanning demonstrates adequate also seen at the site of a prior RFA
ablation zone in caudate lobe defect; this was suspicious for
recurrent HCC and was also ablated
16. On-table Management 4
• An inadequate zone of ablation can be identified, allowing
immediate further ablation
Case 3: Expected hypodense However, subtle inadequate ablation
ablation zone seen around probe margin seen at superior anterior
margin, prompting probe
repositioning and re-ablation
17. On-table Management 5
• If immediate further ablation is contraindicated, the patient
can be scheduled to return for repeat ablation
Case 4: Nodular arterial enhancement Immediate further ablation was deferred in
seen along posterior margin of ablation this patient who had previously undergone
zone suggesting residual tumor. right hepatic lobe resection. The patient
returned in 1 month for repeat ablation.
18. Part IV. Complications
• An additional advantage of intra-procedural contrast-
enhanced CT is the immediate identification of procedure-
related complications
• Rapid identification facilitates prompt management of
complications, minimizing adverse outcomes
19. Complications
• Immediate RFA-related complications detectable with on-table CT
imaging
– Active extravasation
– Biloma
– Pneumothorax
– Biliary tract injury
RED = Better characterized
– Pericardial effusion with contrast-enhanced CT
– Diaphragmatic injury
– Gastric ulcer/bowel injury
– Hemothorax
– Hepatic infarction
– Renal injury
2. Park MH, et al. Radiographics. 2008 Apr;28(2):279-90.
20. Complications
• Case 1: Pneumothorax
Ablation zone and probe tract Probe placement resulted in a small
visualized following RFA pneumothorax, seen on lung window.
21. Complications
• Case 2: Non-target ablation
– Extension of ablation zone in left lateral portion of liver (image 1) to medial
gastric body wall, which appears partially ablated (image 2)
– Patient was placed on proton pump inhibitors and GI consult obtained; there
was no adverse outcome
22. Complications
• Case 3: Pericardial effusion
– Image 1 demonstrates satisfactory hypodense ablation zone
– Image 2 depicts small pericardial effusion, likely reactive from adjacent
ablation
23. Complications
• Case 4: Hepatic infarction
– Circle indicates zone of ablation
– Peripheral to ablation zone is a geographic region of non-enhancement
(arrows), which represents an area of hepatic infarction
– Portal venous gas is a benign finding commonly seen post-ablation
5. Oei T, et al. Radiology. 2005 Nov;237(2):709-17.
24. Complications
• Case 5: Diaphragmatic injury
– Small focus of contrast extravasation is seen into the right pleural space, likely
related to diaphragmatic injury from ablation needle
– Patient was kept in CT and closely monitored; repeat CT 15 minutes later
showed no enlargement in small hemothorax
25. Complications
• Case 6: Peritoneal hemorrhage
– Arterial phase contrast CT following biopsy and RFA of segment 7 hypervascular lesion
demonstrates small areas of arterial bleeding at the peripheral margin of the right
hepatic lobe and within the perihepatic hematoma
– Patient subsequently underwent angiography (next slide)
26. Complications
• Case 6: Peritoneal hemorrhage cont’d
– Image 1: Right hepatic angiogram demonstrates active extravasation supplied
by segment 7 hepatic artery, at site of ablation. Right hepatic artery is
replaced and arises from the SMA.
– Image 2: Right hepatic angiogram following embolization with Embospheres
and gelfoam. No further extravasation was seen.
27. Summary
• In the 217 reviewed cases in which contrast-enhanced CT “on the table”
was incorporated as part of the liver RFA procedure there were:
– 6 instances of incomplete/inadequate ablation
– 4 cases in which new enhancing lesions were identified
– 1 case of non-target ablation
– 8 hematomas/bleeds – 6 were small and required no interventional
management; 2 cases required embolization and are illustrated later
– 2 pneumothoraces, both of which required chest tube placement
– 1 pericardial effusion
– 1 instance of pneumobilia
• On-table management was affected in 8 instances by the findings of the
contrast-enhanced CT, approximately 3.7% of total cases
• Post-procedure management affected in 11 instances, approximately 5.2%
of total cases
28. Conclusion
• Intra-procedural contrast-enhanced CT during percutaneous liver
RFA is easily performed and offers several practical benefits
• Advantages include the identification of additional lesions or
incomplete ablation, which can dictate further on-table treatment
or planning of future treatment sessions
• An additional benefit is the immediate identification of
complications, which directs patient management and minimizes
adverse outcomes
29. References
1. Choi H, Loyer EM, DuBrow RA, Kaur H, David CL, Huang S, Curley S, Charnsangavej C. Radio-frequency ablation
of liver tumors: assessment of therapeutic response and complications. Radiographics. 2001 Oct;21 Spec No:S41-
54.
2. Park MH, Rhim H, Kim YS, Choi D, Lim HK, Lee WJ. Spectrum of CT findings after radiofrequency ablation of
hepatic tumors. Radiographics. 2008 Mar-Apr;28(2):379-90; discussion 390-2.
3. Lim HK, Choi D, Lee WJ, Kim SH, Lee SJ, Jang HJ, Lee JH, Lim JH, Choo IW. Hepatocellular carcinoma treated with
percutaneous radio-frequency ablation: evaluation with follow-up multiphase helical CT. Radiology 2001
Nov;221(2):447-54.
4. Rhim H, Yoon KH, Lee JM, Cho Y, Cho JS, Kim SH, Lee WJ, Lim HK, Nam GJ, Han SS, Kim YH, Park CM, Kim PN,
Byun JY. Major complications after radio-frequency thermal ablation of hepatic tumors: spectrum of imaging
findings. Radiographics 2003 Jan-Feb;23(1):123-34; discussion 134-6.
5. Oei T, vanSonnenberg E, Shankar S, Morrison PR, Tuncali K, Silverman SG. Radiofrequency ablation of liver
tumors: a new cause of benign portal venous gas. Radiology 2005 Nov;237(2):709-17.
