Hepatic Surgery: Portal Vein Embolization
Portal vein Embolizations (PVE) is commonly used in the patients requiring extensive liver resection but have insufficient Future Liver Remanescent (FLR) volume on preoperative testing. The procedure involves occluding portal venous flow to the side of the liver with the lesion thereby redirecting portal flow to the contralateral side, in an attempt to cause hypertrophy and increase the volume of the FLR prior to hepatectomy.
PVE was first described by Kinoshita and later reported by Makuuchi as a technique to facilitate hepatic resection of hilar cholangiocarcinoma. The technique is now widely used by surgeons all over the world to optimize FLR volume before major liver resections.
PVE works because the extrahepatic factors that induce liver hypertrophy are carried primarily by the portal vein and not the hepatic artery. The increase in FLR size seen after PVE is due to both clonal expansion and cellular hypertrophy, and the extent of post-embolization liver growth is generally proportional to the degree of portal flow diversion. The mechanism of liver regeneration after PVE is a complex phenomenon and is not fully understood. Although the exact trigger of liver regeneration remains unknown, several studies have identified periportal inflammation in the embolized liver as an important predictor of liver regeneration.
PVE is technically feasible in 99% of the patients with low risk of complications. Studies have shown the FLR to increase by a median of 40–62% after a median of 34–37 days after PVE, and 72.2–80% of the patients are able to undergo resection as planned. It is generally indicated for patients being considered for right or extended right hepatectomy in the setting of a relatively small FLR. It is rarely required before extended left hepatectomy or left trisectionectomy, since the right posterior section (segments 6 and 7) comprises about 30% of total liver volume.
PVE is usually performed through percutaneous transhepatic access to the portal venous system, but there is considerable variability in technique between centers. The access route can be ipsilateral (portal access at the same side being resected) with retrograde embolization or contralateral (portal access through FLR) with antegrade embolization. The type of approach selected depends on a number of factors including operator preference, anatomic variability, type of resection planned, extent of embolization, and type of embolic agent used. Many authors prefer ipsilateral approach especially for right-sided tumors as this technique allows easy catheterization of segment 4 branches when they must be embolized and also minimizes the theoretic risk of injuring the FLR vasculature or bile ducts through a contralateral approach and potentially making a patient ineligible for surgery.
However, majority of the studies on contralateral PVE show it to be a safe technique with low complication rate. Di Stefano et al. reported a large series of contralateral PVE in 188 patients and described 12 complications (6.4%) only 6 of which could be related to access route and none precluded liver resection. Site of portal vein access can also change depending on the choice of embolic material selected which can include glue, Gelfoam, n-butyl-cyanoacrylate (NBC), different types and sizes of beads, alcohol, and nitinol plus. All agents have similar efficacy and there are no official recommendations for a particular type of agent.
Proponents of PVE believe that there should be very little or no tumor progression during the 4–6 week wait period for regeneration after PVE. Rapid growth of the FLR can be expected within the first 3–4 weeks after PVE and can continue till 6–8 weeks. Results from multiple studies suggest that 8–30% hypertrophy over 2–6 weeks can be expected with slower rates in cirrhotic patients. Most studies comparing outcomes after major hepatectomy with and without preoperative PVE report superior outcomes with PVE. Farges et al. demonstrated significantly less risk of postoperative complications, duration of intensive care unit, and hospital stay in patients with cirrhosis who underwent right hepatectomy after PVE compared to those who did not have preoperative PVE. The authors also reported no benefit of PVE in patients with a normal liver and FLR >30%. Abulkhir et al. reported results from a meta-analysis of 1088 patients undergoing PVE and showed a markedly lower incidence of Post Hepatectomy Liver Failure (PHLF) and death compared to series reporting outcomes after major hepatectomy in patients who did not undergo PVE. All patients had FLR volume increase, and 85% went on to have liver resection after PVE with a PHLF incidence of 2.5% and a surgical mortality of 0.8%. Several studies looking at the effect of systemic neoadjuvant chemotherapy on the degree of hypertrophy after PVE show no significant impact on liver regeneration and growth.
The volumetric response to PVE is also a very important factor in understanding the regenerative capacity of a patient’s liver and when used together with FLR volume can help identify patients at risk of poor postsurgical outcome. Ribero et al. demonstrated that the risk of PHLF was significantly higher not only in patients with FLR ≤ 20% but also in patients with normal liver who demonstrated ≤5% of FLR hypertrophy after PVE. The authors concluded that the degree of hypertrophy >10% in patients with severe underlying liver disease and >5% in patients with normal liver predicts a low risk of PHLF and post-resection mortality. Many authors do not routinely offer resection to patients with borderline FLR who demonstrate ≤5% hypertrophy after PVE.