Portal Vein Embolization

Fig. 7.1

Scheme (a) and CT scan (b) of the future liver remnant (FLR) in a patient undergoing evaluation for an extended right hepatectomy of segment 5–8 + segment 4 and 1. Segments 2 and 3 represent the FLR

Fig. 7.2

Two-stage hepatectomy may be required to clear all metastatic liver disease in the case of multiple bilateral metastases. The FLR, usually segments 2 and 3 (± parts of 1 and 4), is cleared during the first surgical stage, followed by PVE. The sFLR is re-evaluated and if sufficient, the patient can undergo the planned extended right liver resection in a second surgical stage, usually 4–8 weeks after the portal vein embolization (PVE) was performed

Due to the liver volume alterations occurring during embryology, the right liver represents on average 66% of the total liver volume, and left PVE is rarely indicated, as the right hemiliver to be preserved almost always represents sufficient sFLR. The left liver represents on average 33% of the total liver volume, and PVE is required in approximately 10% of patients undergoing right hepatectomy and in 75% of patients undergoing extended right hepatectomy with preservation of only segment 2 and 3 (Figs. 7.3 and 7.4) [4].

Fig. 7.3

Distributions of FLR volume of according to types of major hepatectomy. Adapted from Abdalla EK et al. Surgery 2004 [4] with permission

Fig. 7.4

Contrast-enhanced CT image of patient with colorectal liver metastases undergoing evaluation for PVE. Segments 2 and 3 represent the FLR, with a total volume of 253 ml. The sFLR was 15%, indicating need for PVE before liver resection. *Estimated total liver volume (TEL) is calculated to be 1,686 with the formula TEL = −794.41 + 1,267.28 × body surface area (BSA). LHV left hepatic vein, MHV middle hepatic vein, RHV right hepatic vein, P portal branch to segment, S segment, R ant PV right anterior portal vein

There are two absolute contraindications for PVE: extensive ipsilateral tumor thrombus because most of the portal flow has already been diverted, and clinically evident portal vein hypertension because of the risk of bleeding varicies of the increased portal pressure from the procedure [5]. Renal insufficiency, coagulopathy, advanced liver fibrosis, and main portal vein thrombosis are conditions with increased risk of complication during or after PVE, and should be assessed as relative contraindications [2].

It is likely that as little as 10% sFLR may be sufficient in some patients with normal liver function [6]. However, a number of studies have demonstrated a significant impact on postoperative complications in patients with preoperative sFLR ≤20% [2, 3, 6]. Therefore, sFLR ≤20% is considered an evidence-based cut-off for PVE in the normal liver. The cut-off for preoperative PVE in the injured liver has not been explored to the same extent. However, studies have showed increased rates of postoperative complications and hepatic insufficiency after resection of liver with steatosis or chemotherapy-induced injury [7–9]. Many centers therefore consider the cut-off sFLR <30% an indication for PVE in these patients.

A substantial number of patients with cirrhosis are not candidates for major hepatic resection due to an unacceptable risk of perioperative death. However, patients with Child–Pugh class A cirrhosis are considered for resection if their sFLR is >40%. If sFLR is less than 40% but otherwise resectable, PVE is indicated [10]. This is supported by the findings of a prospective study showing decreased postoperative complications, ICU admissions, and length of hospital stay for patients with chronic liver disease who underwent PVE before resection [11]. Because of the severity of the liver injury occurring, the same cut-off for sFLR (>40%) has been suggested after prolonged biliary obstruction.

Preoperative Assessment of FLR

The FLR must be determined in patients who undergo evaluation for liver resection with a concern for insufficient volume. The most common method of measuring absolute FLR volume is to outline the FLR on axial slices from multiphase contrast-enhanced CT. Based on the area of the outlined FLR and the slice thickness, three-dimensional reconstructions are obtained and the absolute FLR volume can be calculated. However, the absolute FLR volume is inadequate for clinical decision-making, as larger patients require larger FLR. To account for this, most groups now use the ratio FLR to total liver volume (TLV), often termed standardized FLR (sFLR). Only functional non-tumor volume should be included when determining sFLR, and the TLV is calculated directly from three-dimensional computed tomography, subtracting the tumor volume. The main disadvantage with this method is the fact that determining the TLV is time-consuming and may not be accurate in patients with bile duct obstruction.

In our practice, the TLV is based on an estimated TLV (TEL). The TEL is based on the correlation between body surface area (BSA) and total liver volume [12]. Several formulas have been developed, but a meta-analysis found the most accurate to be: TEL =− 794.41 + 1267.28 × BSA [12, 13]. BSA can be calculated using Mosteller’s formula: $BSA=\sqrt{\frac{\mathrm{height}\kern0.5em \left[ cm\right]\times \mathrm{weight}\kern0.5em \left[ kg\right]}{3600}}$ [14]. Furthermore, this method of calculating sFLR (FLR/TEL) has shown correlation with patient outcomes, and thus proven its clinical relevance [2, 6]. At MD Anderson Cancer Center, a web-based calculator has been design-based on these formulas to calculate the sFLR, degree of hypertrophy, and the kinetic growth rate (Fig. 7.5). The correlation between the BSA and the functional liver volume and the formula presented was developed in Western adults in the United States and Europe [12, 13]. It is important to note that TEL can vary between body size and race. Japanese patients have up to 19% larger livers compared to Caucasians for a given body weight. In some centers, especially in Asia, three-dimensional computer models are increasingly used to calculate FLR and sFLR based on the total liver volume.

Fig. 7.5

Web-based calculator used to determine the degree of hypertrophy and kinetic growth rate (KGR) after PVE. Segment volumes are in ml (cm³). Numbers are representative for a patient undergoing right PVE. The formulas used to calculate body surface area (BSA) [14] and total estimated liver volume (TEL) [12] are: $BSA=\sqrt{\frac{\mathrm{Height}\kern0.5em \left[ cm\right]\times \mathrm{weight}\kern0.5em \left[ kg\right]}{3600}}$ and TEL = 794.41 + 1267.28 × BSA. The calculations used to generate the output are: ${}^1 Pre\kern0.5em \mathrm{EMBO}\kern0.5em \mathrm{sFLR}\kern0.5em \left( CT\#1\right)=\frac{Seg2+ Seg3\left(+ Seg4\right)\left(+ Seg1\right)}{Pre\kern0.5emTEL}$ and ${}^2\mathrm{Post}\kern0.5em \mathrm{EMBO}\kern0.5em \mathrm{sFLR}\kern0.5em \left( CT\#2\right)=\frac{Seg2+ Seg3\left(+ Seg4\right)\left(+ Seg1\right)}{\mathrm{Post}\kern0.5emTEL}$ and ³Degree of Hypertrophy = Post EMBO sFLR − Pre EMBO sFLR and ${}^4\mathrm{Kinetic}\kern0.5em \mathrm{growth}\kern0.5em \mathrm{rate}\kern0.5em (KGR)=\frac{\mathrm{Degree}\kern0.5em \mathrm{of}\kern0.5em \mathrm{Hypertrophy}}{\mathrm{Weeks}\kern0.5em \mathrm{Between}\kern0.5emCT\#2\kern0.5emand\kern0.5emPVE}$

The sFLR is estimated before and 3–4 weeks after PVE. If sFLR after PVE meet the resectability criteria, it is generally accepted that the planned resection can be performed within accepted risk of adverse events. At MD Anderson Cancer Center, the following cut-offs are used for FLR resectability criteria: normal liver >20%, liver pretreated with more than 3 months of chemotherapy >30%, cirrhosis >40% (Fig. 7.6) [6, 15–19]. While cirrhosis is rare in patients with CLM, an increasing number are heavily pretreated with chemotherapy. Obesity is increasing worldwide, and hepatic steatosis is also a more common finding which require >30% FLR for safe resection [17].

Fig. 7.6

Requirements for FLR depends on the underlying liver function. In the presence of liver injury, increased FLR is needed to allow safe liver resection with acceptable risk of hepatic insufficiency and death. ¹Abdalla et al. Arch Surg 2002, ²Vauthey et al. Ann Surg 2004, ³Azoulay et al. Ann Surg 2000, ⁴Kubota Hepatology 1997. CTX chemotherapy BMI body mass index

Techniques of Portal Vein Embolization

Accessing the Portal Vein

The portal vein can be accessed for embolization during surgery, but with the increased experience within the field of interventional radiology, the percutaneous technique is currently the method of choice in most centers. Surgical PVE is usually performed via the ileocolic vein, while percutaneous PVE is performed ultrasound-guided transhepatic with catheter access through a distal branch of the ipsilateral or contralateral portal vein. The ipsilateral approach is often chosen due to safety reasons, as the FLR is left without risk of damage [20]. However, the ipsilateral approach may be technically more challenging, and holds a greater potential of peritoneal spillage of tumor cells. Reverse-curve catheters can be used to facilitate access to the segmental branches and cope with the increased technical challenge with the ipsilateral approach (Fig. 7.7).

Fig. 7.7

Ipsilateral right portal vein embolization with embolization of segment 4 portal vein branches. The portal vein is entered via a distal branch of the right posterior portal vein, and the segment 4 embolization (a) is performed before embolization of the right posterior (b) and anterior (c) portal vein branch. The access tract is embolized to prevent capsular hemorrhage. Care should be taken to avoid puncturing tumor tissue due to potential peritoneal spillage of cancer cells when using the ipsilateral approach

Agents Used for Embolization and the Technique

Agents used to embolize the portal vein must be easy and safe to deliver, cause complete occlusion preferably without any recanalization, and be well tolerated by the patient. A number of agents have been used to induce portal vein embolus, including n-butyl cyanoacrylate (NBCA) and ethiodized oil, fibrin glue, ethanol, and microparticles such as polyvinyl alcohol or trisacryl gelatin. To date, no study has convincingly demonstrated the superiority of any those, and the choice of agent is mostly operator-determined. After the PVE catheter has been maneuvered into place, the vascular sheet is secured and a flush portography is performed to assess the portal anatomy. The portal pressure is measured before the embolization takes place. At MD Anderson Cancer Center, a combination of trisacryl gelatin microspheres of various sizes and embolization coils are used. Small caliber microspheres are used initially to embolize smaller distal portal vein branches, followed by larger caliber microspheres in larger proximal portal vein branches. Upon complete stasis, embolization coils are placed proximally to prevent recanalization. Care must be taken in every step not to embolize non-target branches of the portal vein.

Embolization of Segment 4 Portal Vein Branches

Extended right hepatectomy involves resection of the middle hepatic vein and segment 4 or parts of segment 4. In cases where the left lateral section (segment 2 and 3) constitute the FLR, right PVE may not always ensure sufficient volume. This led to the idea that the superior and inferior segment 4 portal vein branches form the left portal vein could be co-embolized to increase atrophy of as much liver tissue to undergo resection as possible, and subsequently induce even further hypertrophy of the FLR (Figs. 7.7 and 7.8). Furthermore, segment 4 is at risk of increased growth in conventional right PVE, which may be unsuitable if segment 4 contains tumor and is planned to undergo resection [21, 22]. Since the late 1990s, several groups have published a significant increase in the degree of hypertrophy when segment 4 portal vein branches were co-embolized with the right portal vein (Fig. 7.9) [23, 24].

Fig. 7.8

Portogram with the catheter in the right portal vein before PVE showing a contrast-filled right portal vein three. Portogram with the catheter placed in the main portal vein after right PVE and embolization of segment 4 branches. White arrows indicate coils in the segment 4 branches. Black arrows indicate the right anterior and right posterior portal vein. Adapted from Madoff DC et al. J Vasc Interv Radiol 2005 [37] with permission

Fig. 7.9

Contrast-enhanced CT 4 weeks after right PVE with segment 4 embolization. The latter caused atrophy of segment 4 and increased hypertrophy of the left lateral segments, which in this patient represented the future liver remnant (FLR)

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