Radiofrequency Ablation of Liver Tumors

Transcription

1 Radiofrequency Ablation of Liver Tumors Michael M. Awad, Michael A. Choti Indications and Contraindications Indications Unresectable malignant tumors of the liver (e.g., hepatocellular carcinoma, colorectal metastases, neuroendocrine tumors, selected other types of metastases) Tumors <5cm in size (most effective for lesions <3cm) Palliative treatment of symptomatic tumors (e.g., neuroendocrine metastases) Bridge to liver transplantation (hepatocellular carcinoma) Access: Open: In combination with resection When resection is planned, but unresectability is found at time of laparotomy In difficult locations or selected cases when multiple ablations are required percutaneus: not discussed in this atlas Laparoscopic: Patient fulfills basic requirements to undergo surgery Lesion(s) amenable to laparoscopic approach percutaneus: not discussed in this atlas Contraindications Extrahepatic disease (unless extrahepatic sites are resectable or when there is palliative indication) Perihilar tumor location Significant coagulopathy or thrombocytopenia Ascites Previous bilio-enteric anastomosis (relative contraindication due to the increased risk of hepatic abscess following radiofrequency ablation, RFA) Preoperative Investigation and Preparation for the Procedure CT or MRI: Assessment to rule out resectability and determine if lesions are ablatable PET: Evaluation for presence of extrahepatic disease (e.g., colorectal metastases) In operating Grounding pads (varies depending on RFA manufacturer) room: Place greater than 50cm from electrode Orient pads with long axis perpendicular to body axis Use multiple pads when indicated

2 410 SECTION 3 Liver Guidance Imaging Modality Imaging is used for lesion localization, probe guidance, and ablation monitoring. The following features of each imaging modality must be considered. Ultrasound Most common method used Inexpensive and real time feedback Sometimes difficult to visualize lesion adequately Increased echogenicity from microbubbles Microbubbles are not a true representation of zone of coagulation necrosis Echogenicity may obscure further needle positioning Alternatives: CT or MRI Transaxial needle track required CT fluoroscopy is a useful adjunct For MRI, a compatible RFA needle is required Probe Selection A number of different probes are commercially available for performing RFA (A-1, A-2, A3). Probes are typically gauge, 15 25cm long, insulated cannulas containing one to three straight needle electrodes (ValleyLab) or five to ten individual hook-shaped electrode arms or tines (RITA Medical, Boston Scientific). Some of the newer probes have a cooled-tip system utilizing circulating saline (ValleyLab, Berchtold), or local saline infusion (RTA Medical). A-1 A-2 A-3

3 Radiofrequency Ablation of Liver Tumors 411 Procedures Open Technique STEP 1 Access and assessment of tumors Incision, evaluation, palpation and mobilization of the liver are performed as for a liver resection. The abdomen is explored for the presence of extrahepatic disease and the evaluation is completed by intraoperative ultrasound (IOUS) to identify/confirm the location and the size of the lesions (A). The feasibility of the ablation is determined and the number of needed ablations is calculated. STEP 2 Placement of the probe and ablation of tumors The probe is aligned so that its trajectory lies in the plane of the ultrasound image and does not intersect vital structures such as blood vessels and bile ducts. It is advanced under image guidance until the tip is either close to the proximal edge of the tumor or near the distal edge, depending on the probe type (B-1). The deployed probe is visualized in perpendicular view to confirm adequate tip position and deployment (A). The probe tines are deployed and radiofrequency energy is applied according to the manufacturer s directions (B-2, B-3).

4 412 SECTION 3 Liver STEP 3 Ablation of large or irregularly shaped lesions and tract ablation For large or irregularly shaped lesions, multiple ablations may be needed (Step 2 is repeated as necessary). A pattern of overlapping spheres or cylinders is used to cover the lesion while maintaining adequate margins. With some devices, tract ablation is performed to cauterize the tract and to minimize seeding. The probe is withdrawn 1cm at a time in tract ablation mode on the radiofrequency generator, allowing temperature to reach >70 C at each step. This is continued until the probe is completely removed.

5 Radiofrequency Ablation of Liver Tumors 413 Laparoscopic Approach STEP 1 Positioning of the patient and access Depending on the location of the tumor(s), the patient is placed in the supine or left lateral decubitus position. A minimum of two laparoscopic trocars are placed: a 12-mm periumbilical camera port and a 12-mm laparoscopic ultrasound port in the right flank. The radiofrequency probe can be placed percutaneously, through a sheath, or through a 5-mm right subcostal port. More ports may be required if additional procedures are to be performed (e.g., liver mobilization, partial resection) (A-1). A-1

6 414 SECTION 3 Liver STEP 2 Assessment of tumors and ablation Laparoscopic intra-abdominal ultrasound (IOUS) is performed by either rigid or flexible IOUS probes to identify/confirm the location and the size of the lesions. The abdomen is explored for the presence of extrahepatic disease. As described for the open technique, the RFA probe is oriented parallel with the IOUS crystal to facilitate probe guidance (A-2). Limited mobility can make this more difficult than with the open technique. The ablation process and monitoring is otherwise performed as described with the open approach.

7 Radiofrequency Ablation of Liver Tumors 415 Postoperative Testing Follow-up postablation imaging (CT or MRI) is performed 3 7days after procedure to assess completeness of ablation. Postoperative Complications Short term: Pleural effusion Regional hemorrhage into needle track or into RFA lesion Fever Hepatic abscess (more common with enterobiliary anastomosis) Biliary stricture secondary to ablation near major bile duct Grounding pad burns Long term: Biloma Biliary fistula Ascites Hepatic insufficiency Arteriovenous fistula Tricks of the Senior Surgeon When the lesion lies near a major blood vessel, thermal energy from the probe may be drawn away from the ablation zone, limiting ablation efficacy. This is known as the heat-sink effect. This can be limited using in-flow occlusion techniques (e.g., Pringle maneuver) or repositioning the array closer to the vascular structure. Stabilization of the radiofrequency probe at the skin or liver surface should be done during deployment to avoid push back. Depending on the device, monitoring of the impedance pattern and tine deployment shape by ultrasound can confirm success of the ablation in real time. With some devices, temperature profiles can also be helpful at confirming successful ablation, including consistent tine temperatures and adequately slow cool-down temperatures.