Precise Ablation Of The Segmental Glissonian Pedicle By Ultrasound-guided Radiofrequency In Anatomic Liver Resection

BACKGROUNDWith people's deeper understanding of liver anatomy, physiology and pathology as well as the further improvement of surgical technique, the concept of precision liver resection has been promoted recently. It pursues the result of the complete removal of the lesions, maximum preservation of functional liver, minimum blood loss and trauma invasiveness. For the hepatic lesions distributed by segmental-base, such as HCC and hepatolithiasis, anatomic segmentectomy is the most optimum surgical option to achieve the objectives of precision liver resection. The technique of segmentectomy was originally introduced by Makuuchi et al. It has been achieved equivalent long term survival to more radical resection techniques. Control of the inflow vessels and delineation of the relevant segment prior to resection has been achieved by several techniques. The most widely used technique is the puncture technique proposed by Makuuchi et al in1981. Indigo-carmine is injected into the vessel under IOUS-guidance, and the demarcated area for resection becomes evident on the liver surface. Other methods proposed include balloon catheters inserted transhepatically to occlude the feeding portal branch, or, more recently, through the mesenteric vein. The main limitation of these techniques is the high standard of skill required to puncture and occlude small vessels. Mazziotti et al proposed an intraparenchymal approach and ligation of the segmental Glissonian pedicle.This technique may be associated with intra operative blood loss and lengthy operation time. Navarra et al have recently suggested ablation of the segmental Glissonian pedicle by applying radiofrequency under ultrasound guidance. This was performed using the Habib sealer, a rectangular instrument using two rows of RFA probes. This technique however has certain limitations. It does not allow precise location of the target vessels and may be associated with inadvertent damage to other structures. The technique described is a modification of the Navarre procedure. It uses a single cooled-tip electrode, allowing precise targeting of the segmental vessels under IOUS guidance. It has several potential advantages:it is easy to operate and able to be performed by most HPB surgeons or radiologists familiar with intra operative ultrasound and liver anatomy; it minimizes intra operative blood loss and operative times; it may theoretically avoid tumour dissemination through the portal venous system by occlusion of the segmental vessels prior to parenchymal resection. This article reports an assessment of this technique in a preclinical study using a porcine animal model.MATERIALS AND METHODS1. Animals and Groups:The study was carried out on12Bama miniature pigs, with an average weight of25-35kg. The animals were divided into2groups. Group A: precise ablation of segmental glissonian pedicle by ultrasound-guided radiofrequency (6pigs); Group B:precise ablation of segmental glissonian pedicle by ultrasound-guided radiofrequency while the hepatic artery was clamped (6pigs).2. Surgical Procedure and Intraoperative Monitoring:According to the segmental nature of the porcine liver as delineated by Court F. G. et al, resections of segment Ⅲ, V and VI were performed.1)A J-shaped right subcostal incision was performed.2)Cholecystectomy was done routinely to eliminate the potential of radiofrequency induced injury.3)Intraoperative ultrasound (IOUS) was used to scan the intrahepatic vascular anatomy and identify the target liver segmental arterial and portal branches. Coagulative destruction of the feeding vessels was induced with the application of a "cooled-tip" RF with a500kHz-RF Generator. The target radiofrequency point in the segmental portal branch was chosen to be at least2cm distance from the segmental bifurcation. The radiofrequency was ceased when ischemic demarcation of the liver segment was observed. We took down the radiofrequency time and then measured the diameter of the hypoechoic region and the flow rate of the segmental arterial and portal branches which we had ablated and the adjacent liver segmental arterial and portal branches by ultrasound.4)The liver parenchyma is resected by the clamp-crush method without any form of hepatic inflow occlusion.For group B, the hepatic artery was identified and clamped temporarily during application of the RFA.3. Postoperative Monitoring:The animals were kept in boxes on-site14days after operation. Plasma samples were withdrawn from a central venous catheter on the first and14th postoperative days. Hepatocellular injury was assessed by standard laboratory assays of aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Other recorded serum parameters were y-glutamyltransferase (y-GT), alkaline phosphatase(ALP), bilirubin, albumin.In the14th postoperative day, Laparotomy was done to explore any procedure related complications such as biliary fistula, ascites, hepatic abscess, peritoneal haemorrhage. The flow rate of the arterial and portal branches of the remnant segments was documented. A total hepatectomy was then done to observe the histological change of the remnant segmental arterial, portal and biliary tract branches.4. Histology:all of the segments including the target segments and the remnant segments which were resected in the14th postoperative day were sliced into thin sections of5-mm thick perpendicular to the glissonian pedicle long axis. Hematoxylin and eosin (H&E) staining was done to observe the pathologic changes of segmental arterial, portal and biliary tract branches.5. Data Analysis:The One-Way ANOVA test and the χ2test were used for the continuous and the categorical data, respectively. The significance level for all tests was fixed at P≤0.05. The statistical analyses were performed using spss16.0.2software.RESULTS1. Feasibility:In the12pigs, the precise puncture of the electrode was successfully applied without any technically-related inconvenience. A total of36hepatic segments were resected (18of group A,18of group B). In group A,15areas of marked discoloration on the surface of liver were obvious,3areas (1of segment Ⅲ,2of segment V) were not obvious (Fig.7). In group B, all of the areas of marked discoloration were obvious, the effect of demarcation was significantly better than that in group A (P＝0.000). Radiofrequency time was set at300seconds for the3 unobvious areas. Except these3areas, the average radiofrequency time was124.0±36.2seconds. The radiofrequency time was similar between the2groups (133.0±34.7versus117±36.6seconds; P>0.05).2. General Clinical and Biological Tolerance:Tolerance of the procedure was excellent and recovery was uneventful. No septic or cardiovascular, respiratory complications. Postoperative mortality was nil. In the14th postoperative day, laparotomy was performed, with no evidence of complications such as biliary fistula, ascites, hepatic abscess and peritoneal haemorrhage. Immediately after resection, all serum parameters of hepatocellular injury were elevated. Peak values were observed in all groups on the first postoperative day, and all parameters had normalized by day14.3. Blood Flow of the Target and Remnant Segmental Vessels:The flow rate of the target segmental portal branches was0cm/s after radiofrequency. The flow rate of the arterial branches was significantly reduced compared to before radiofrequency. However, most of the arterial branches blood flow could still be detected after radiofrequency. There was only1segmental arterial branch (segment V) with a flow rate of Ocm/s in group A versus6segmental arterial branches (3of segment Ⅲ,1of segment V and2of segment VI) in group B after radiofrequency. The flow rate of the arterial branches after radiofrequency in group B was lower than that in group A. In all groups, there was no significant difference in the flow rate of the segmental arterial and portal branches (remnant segments) among pre-radiofrequency, post-radiofrequency and14days after operation.4. Ultrasound Imaging: All of ablation zones in the liver were seen as a hypoechoic region with a central hyperechoic zone. The mean diameter of the hypoechoic regions measured by ultrasound was1.52±0.17cm (1.49±0.19versus1.55±0.14cm;P>0.05).5. Histology:Using standard hematoxylin and eosin staining, histologic evaluation of formalin fixed paraffin-embedded sections of the target segments revealed evidence of damage to the segmental glissonian pedicle. There was prominent heat injury in the tunica media and tunica intima of the portal veins. The injured portal veins measured1.67±0.43cm (group A:1.64±0.38versus group B:1.69±0.49cm;P>0.05). There was prominent heat injury in the tunica adventitia and the outer portion of tunica media of the hepatic artery, and there was mild injury in the endothelium. The damaged arteries measured1.33±0.40cm (group A:1.25±0.35versus group B:1.42±0.43cm; P>0.05). Severe injury was identified in the out portion of the tunica media and the epithelium of the bile duct; and less severe injury was identified in the inner portion of the tunica media. The injured bile ducts measure1.65±0.35cm (group A:1.67±0.34versus group B:1.64±0.38cm;P>0.05). Histologic evaluation of sections of the remnant segments which were resected on the14th postoperative day revealed that there was no injury to other adjacent arterial, portal and biliary tract branches.CONCLUSIONS1. The technique described in this article was evaluated on a porcine model. The feasibility and safety of the technique was confirmed. No mortality or morbidity occurred, Liver function tests of hepatocellular injury recovered by day14in both groups. There was no histological damage nor any significant change to the flow rate of the non targeted segmental arterial, portal or biliary duct structures observed to day14.2. Temporary occlusion of the hepatic artery adds further benefit in the effect of demarcation and there was no significant difference in the volume of ablation zones or hepatocellular damage between the two groups.3. Careful attention to technical details is essential. Considering mechanism of radiofrequency ablation, precise location of the tip using IOUS adjacent to the target vessel to make maximal use of the radiofrequency energy is essential and avoids the technically demanding intra luminal access as described by Makuuchi et al. Histologic evaluation of5-mm thick continuous sections revealed the mean ablated length of segmental arterial, portal and biliary tract branches was less than2cm. The probe in fact needs to be at least1.5cm away from vessels feeding segments not to be resected or structures that need to be left intact to avoid thermal injuries that can lead to postoperative vascular or biliary complications.4. The herein proposed technique of precise ablation of the segmental glissonian pedicle by ultrasound-guided radiofrequency has been used with success in experimental animals so far, confirming the technique to be quick, safe and effective. We believe that the technique could have a wide implication and potential in liver surgery.