ABSTRACT
A transjugular intrahepatic portosystemic shunt (TIPS) is one of the most challenging procedures in interventional radiology. Hepatic and portal venous anatomy can be highly variable, and access to the portal vein, which can be quite difficult even for experienced surgeons, is the most critical step in a TIPS. Although there are multiple techniques to achieve a portal venous puncture, each access technique carries a unique set of risks and benefits. Thus, knowledge of these assistive techniques will add to the resources available to the surgeon when planning and subsequently performing a TIPS and, ultimately, increase the likelihood of a safe and successful procedure.
Main points
• Multiple techniques exist to assist in portal venous puncture during a transjugular intrahepatic portosystemic shunt.
• Each portal vein access technique carries a unique set of risks, benefits, advantages, and disadvantages.
• Knowledge of these techniques increases the likelihood of a safe and successful procedure.
A transjugular intrahepatic portosystemic shunt (TIPS) is one of the most challenging procedures in interventional radiology. It entails the creation of a shunt between the portal and hepatic venous systems, and access into the portal venous system is the critical step in a TIPS creation. Multiple techniques have been described concerning portal venous access, and each one carries a unique set of risks and benefits. The purpose of this article is to investigate the different techniques that have been described for portal venous access during a TIPS procedure.
Access techniques in patients with a patent portal vein
Direct and indirect portograms
The direct portogram technique was one of the first described techniques for guiding portal vein access during a TIPS procedure. This technique requires the placement of a catheter into a patent portal vein branch. The catheter is advanced into the main portal vein, and contrast is injected to demonstrate the portal venous anatomy. Direct access to the portal vein can be obtained by using an ultrasound-guided transhepatic approach or by ultrasound-guided access into a patent paraumbilical vein (Figure 1). An indirect portogram is another of the first described TIPS guiding techniques. A high-quality portal venogram is obtained by imaging the venous phase of a selective power injection of contrast into the superior mesenteric artery. Figure 2 illustrates the indirect portogram technique.
Iodinated contrast wedge portogram
With this technique, a contrast wedge portogram is obtained by injecting iodinated contrast through an end-hole catheter placed in a wedged position in the distal hepatic vein (Figure 3). Some of the iodinated contrast will pass through the sinusoids resulting in opacification of the portal venous system. Using this technique, the main portal vein is seldom opacified because of the viscous nature of the iodinated contrast. Krajina et al.1 found that a wedged contrast portogram resulted in the visualization of the bifurcation of the portal vein in 25% of patients, while only part of the portal vein was visualized in 36% of patients, and there was no portal vein opacification in 39% of patients. The major drawback of this technique is that the injected iodinated contrast can dissect into the liver parenchyma, resulting in permanent staining and obscuring visualization of the relevant vascular anatomy later in the procedure. This technique also carries the risk of liver laceration with capsular perforation.
CO2 wedge portogram and direct parenchymal CO2 injection
A CO2 wedge portogram is a very effective technique to map the position of the portal vein. The CO2 wedge portogram is obtained by placing either an end-hole catheter or an occlusion balloon in the wedged position in the distal hepatic vein and gently injecting 10–15 mL of CO2 (Figure 4). The two techniques are comparable, although it has been proposed that the occlusion balloon technique could be safer. Multiple studies have shown CO2 to be a useful contrast agent for opacification of the portal venous system during a TIPS. Krajina et al.1 demonstrated that the use of CO2 leads to superior visualization of the portal vein compared to iodinated contrast during wedged hepatic venography due to the less viscous nature of CO2. Using CO2 as the contrast medium for wedged hepatic venography, opacification of the portal vein bifurcation was seen in 87% of patients, and there was no visualization of the portal venous system in 7% of patients, compared with 25% and 39%, respectively, when an iodinated contrast medium was used. Additionally, the CO2 does not stain the liver parenchyma, but, as with the previous technique, liver laceration with capsular rupture is a risk of this procedure.
Direct parenchymal injection of CO2 can be used as an alternative to a CO2-wedged hepatic venogram. This technique is useful when the portal vein is not visible after a CO2-wedged venogram during a TIPS procedure (Figure 5) and involves advancing the transhepatic needle into the liver parenchyma. This is followed by a gentle injection of 10–15 mL of CO2 directly into the parenchyma. Forceful injection of CO2 should be avoided due to the risk of capsular rupture. An alternative technique is to perform a direct ultrasound-guided transhepatic puncture with a 21-gauge Chiba needle directly into the liver parenchyma and gently inject 10–15 mL of CO2.
Percutaneous portal venous access
Percutaneous portal venous access is a localization technique that is useful in instances where an adequate contrast portogram cannot be achieved. A peripheral branch of the portal vein is punctured under ultrasound guidance. This is followed by the placement of a snare or a wire that can be used as a target for puncture. Alternatively, a snare or wire can be placed into the portal vein by first percutaneously accessing the splenic vein or a patent umbilical vein (Figure 6). A balloon occlusion catheter can be used as a target as well, instead of a snare or wire. The authors have not used this technique. In a 2021 study, Cam et al.2 examined the effect of different techniques of portal vein cannulation during a TIPS placement on procedure efficiency. The study demonstrated that percutaneous portal vein guidewire placement for fluoroscopic targeting during a TIPS was associated with shorter procedure times, shorter fluoroscopic times, and potentially decreased complications when compared to more traditional fluoroscopically-guided wedged hepatic portography.
Intravascular sonographic imaging
The use of an intravascular ultrasound (IVUS) probe to obtain intravenous ultrasound images is a newer technique that involves using a catheter with a miniature ultrasound probe at the tip to assist in locating and puncturing the portal vein (Figure 7). The advantages of this technique include the ability to adjust the trajectory of the puncture and visualize the needle puncturing the portal vein based on real-time visualization with a level of spatial and anatomic detail that is not possible when utilizing fluoroscopy alone. In a 2016 study, Pillai et al.3 compared the safety and effectiveness of IVUS–guided portal vein access during a TIPS with conventional TIPS techniques. The study showed that IVUS–guided portal vein access during a TIPS procedure is associated with shorter portal vein access times, decreased needle pass-related capsular perforations, and reduced radiation dose when compared to conventional TIPS techniques. Recently, the intracardiac echocardiography (ICE) catheter has become the preferred tool for performing sonographic imaging guidance during a TIPS. With either jugular or femoral access, the ICE catheter can be advanced to the level of the intrahepatic inferior vena cava, allowing puncture of the portal vein under live ultrasound imaging.4 The use of the ICE allows the surgeon to increase the safety and technical success of the procedure by maximizing the accuracy of the portal vein puncture while also decreasing the radiation time and contrast dose.4
Overlay technique
The overlay technique involves superimposing cross-sectional imaging [magnetic resonance imaging, computed tomography (CT), or cone beam CT] on fluoroscopic imaging to help guide portal vein puncture. A study by Meine et al.5 assessed the technical feasibility, success rate, puncture complications, and procedural characteristics of a TIPS using a three-dimensional vascular map overlay based on image registration of pre-procedural contrast-enhanced multidetector CT for portal vein puncture guidance. The study found that a TIPS using registration-based contrast-enhanced multidetector CT vessel information for puncture guidance is feasible and safe. Additionally, this overlay technique was found to have the potential to improve hepatic vein catheterization, increase the ease of portal vein puncture, and decrease radiation exposure for the patient and surgeon.5 The example in Figure 8 utilizes cone beam CT performed in the angiography suite at the time of the procedure to create a plot of the locations of the right hepatic and portal veins, which is then used to direct the needle puncture under fluoroscopy. A drawback of this technique is that patient respiration and/or movement cannot be accounted for, leading to imprecise portal vein targeting.
Additional techniques
Additional techniques have been used to guide portal venous puncture during a TIPS procedure. Blind transparenchymal puncture involves inserting a transparenchymal needle into the hepatic veins in the direction of the anticipated anatomic location of the portal venous system under fluoroscopy without specific additional imaging guidance. However, this technique is not recommended, as it carries an elevated risk of technical failure, multiple unsuccessful puncture attempts, and a higher risk of complications. Additionally, surgically-assisted direct access to the superior mesenteric vein has been described. In this technique, femoral access is used to gain access to the hepatic vein, and a mini-laparotomy is performed to allow for transmesenteric access into the portal venous system.6 While this technique does allow for technical success, the involvement of a surgical team to perform a laparotomy is a logistical challenge. Neither of the aforementioned techniques has been used by the authors in their practice.
Access techniques in patients with a portal vein thrombosis
Transsplenic access to the portal venous system
Transsplenic access is a technique that allows for portal vein access in patients with both acute and chronic portal vein occlusion. A needle is inserted through the spleen into the splenic venous system. Once splenic vein access is established, the occluded portal vein can be recanalized to allow for the subsequent TIPS (Figure 9).7 Transsplenic access is a safe technique. As with transhepatic access, the main complication of concern is bleeding from the access tract leading to a hematoma formation, which can be mitigated by a coil or plug embolizing the transsplenic tract.7
Transabdominal ultrasound guidance
A TIPS under fluoroscopic guidance with additional transabdominal ultrasound guidance is another technique that is particularly useful when patients have acute portal vein thrombosis or when the hepatic venous system is not patent.8 While the technical success rate utilizing this technique is high and the complication rate is low, the use of this technique is limited in obese patients and when ascites is present.8
Complications
Liver laceration with capsular injury is a complication that can occur during hepatic vein wedge or intraparenchymal contrast injection. Carbon dioxide is preferred over iodinated contrast because of the higher rate of main portal vein visualization and its associated lower risk of capsular perforation. Previous research has found that extravasation of contrast occurs at a rate of 1.8% when using CO2 and 7.5% when using iodinated contrast.9 The use of an occlusion balloon catheter for contrast injection may also decrease the risk of this complication by redirecting the flow of the contrast agent over a larger surface area of the liver. Lastly, and perhaps most importantly, the surgeon should always remember that forceful injection of contrast increases the risk of this complication, so the injection of the contrast material should be slow and gentle to decrease the risk of traumatic injury to the liver (Figure 10). If capsular perforation is detected, the surgeon should be prepared to proceed with further intervention to manage the complication.
Puncture of the biliary system, including the gallbladder, is not uncommon during TIPS procedures (Figure 11) and is typically well tolerated. However, there is a 5% chance of creating a fistula between the biliary and vascular systems after an accidental puncture of the biliary system.9 A fistula between the biliary and vascular systems can result in hemobilia, cholangitis, sepsis, and stent infection. In such cases, further intervention, including a biliary diversion via stenting or drainage, may be necessary.9
Accidental arterial puncture (Figure 12) occurs in approximately 6% of TIPS procedures. However, clinically significant arterial puncture only occurs in approximately 2% of cases. Complications associated with arterial puncture include hemorrhage, pseudoaneurysm, dissection or occlusion of the artery, and fistula formation.9 If such complications arise, angiography is the next best step in evaluation, with subsequent embolization if warranted. The surgeon should be careful to avoid dilating a tract between the hepatic vein and hepatic artery as this can result in patient death secondary to a sudden increase in right atrial pressure after arterial to venous shunt creation.10
A possible complication of direct transhepatic or transplenic access to the portal venous system is bleeding through the puncture tract with subsequent perihepatic or perisplenic hematoma. Embolization of the portal vein access tract, with coils or plugs, has proven very effective in preventing this complication.2
Conclusion
There are multiple reported techniques to assist in portal venous access during a TIPS procedure, all of which are aimed at obtaining access into the portal vein with the least number of attempts in the least amount of time. The correct use of these techniques increases the chance of technical success and decreases the chances of complications.