Chapter 20: Doppler Surveillance of Transjugular Intrahepatic Portosystemic Shunts in the Stent-Graft Era

A transjugular intrahepatic portosystemic shunt (TIPS) is an artificially created conduit within the liver that diverts portal flow into the systemic circulation. Normally reserved as the last treatment for decompensated liver disease before liver transplantation, it aims to control variceal bleeding and refractory ascites. As the name suggests, this procedure is performed through a percutaneous access site in the jugular vein, usually on the right side, and provides a much less invasive option to open surgery. First described by Rosch in 1969,1 the TIPS procedure began to exert its role in end-stage liver disease management in the mid-1980s upon the introduction of endovascular stents. In 1988, Rössle et al reported the first successful TIPS deployment in humans.² Since then, it has gained widespread recognition as the mainstay treatment for portal hypertension (PHT) refractory to medical therapy.²

To clarify the appropriate indications for TIPS placement, the American Association for the Study of Liver Diseases (AASLD) has compiled a comprehensive practice guideline for this procedure³ available at www.aasld.org. The contraindications and common indications for TIPS and their recommended use outlined by AASLD are summarized in Table 20.1 and Table 20.2.

The success of the TIPS procedure largely stems from the advent of endovascular stent grafts, which prevent tract closure. The first-generation stent grafts were bare-metal stents, mainly Wallstents (Boston Scientific, Natick, Massachusetts), which were prone to thrombosis or stenosis because of pseudointimal hyperplasia. Stent patency is characterized as either primary or secondary. Primary stent patency refers to the duration a stent remains patent from the time of deployment to first intervention. Secondary stent patency refers to the lifespan of a stent to complete loss of function despite interventions. The primary stent patency rate for earlier generation stents is highly variable but generally low. Two studies cited 2-year primary patency rates of 5%⁴ and 26%.⁵ The secondary patency rate can be quite high, with 83% patency at 5 years reported by one study that monitored long-term stent patency rate.⁶ Stenosis usually occurs within the stent or at the hepatic venous outflow.

Table 20.1 Contraindications to Placement of a Transjugular Intrahepatic Portosystemic Shunt

Subsequent development of expanded-polytetrafluoroethylene (PTFE)-covered endoprostheses (VIATORR Gore-Tex vascular graft, W.L. Gore and Associates) significantly improved stent patency. The covered stent graft is a self-expanding high-radialstrength nitinol stent graft that has a proximal region lined internally by a thin layer of expanded PTFE, which is impermeable to bile and mucin. One end of the stent has an uncovered region. The uncovered region placed in the portal system allows normal blood flow at the portal confluence, and the covered region placed intrahepatically provides an impermeable interface with the hepatic parenchyma. The expanded PTFE lining also reduces in-stent neointimal hyperplasia.7 The stent patency rate is even higher if the stent is extended to the level of the inferior vena cava (IVC).⁸ Ample data show clear survival benefit offered by covered stents compared with bare-metal stents.^9–11 Surprisingly and against intuition, covered stents are also associated with a decreased incidence of hepatic encephalopathy (HE),¹² which was initially expected to be higher given the improved stent patency rate.

Variceal bleeding occurs in the setting of advanced liver cirrhosis complicated by PHT. First-line therapy for variceal bleeding consists of a combination of pharmacologic and endoscopic treatments, including vasoactive medication, prophylactic antibiotics, and endoscopic band ligation or injection sclerotherapy. In severe cases, transfusion may also be needed. Patients with hepatic venous pressure gradients (HVPGs) of 20 mm Hg or more are at high risk for treatment failure.¹³ TIPS is highly effective in controlling acute variceal bleeding, including the high-risk patient population, and can be used as rescue therapy if first-line treatments fail. Hemostasis is generally achieved when the HVPG is reduced to 12 mm Hg or less. This conventional treatment algorithm is now under challenge by recent data from a multicenter study, which found significant survival benefit in high-risk patients with cirrhosis when TIPS was deployed early.¹⁴

In addition to controlling variceal bleeding, TIPS effectively reduces ascites refractory to diuretic therapy. Left untreated, refractory ascites often progresses to hepatorenal syndrome and hydrothorax. Although these conditions are treatable by large-volume paracentesis (LVP) and pleurodesis, reaccumulation of fluid can be expected. These procedures also carry the risk of progressive circulatory dysfunction, eventually leading to hepatorenal syndrome. Each procedure also carries inherent technical risks. Assuming there are no stent graft complications, ascites resolves within 1 month after TIPS placement. Patients are able to enjoy a longer ascites-free window than that offered by LVP. With amelioration of total body fluid shift, the renal function also improves.

Post-TIPS HE is a common occurrence, reported to occur in 5% to 35% of patients.¹⁵ The nitrogenous compounds from the gastrointestinal tract, in particular ammonia, gain direct systemic access through a patent TIPS. A decrease in the caliber of the stent (available in 8-, 10-, and 12-mm diameters) theoretically reduces the risk of HE. However, this is not well supported by current data, and a recent study¹⁶ found no difference in the rate of HE when comparing 8- and 10-mm stents. Furthermore, the 8-mm stent was ineffective in portal decompression. Fortunately, the vast majority of patients with post-TIPS HE are successfully treated with conservative management. A small percentage of patients are refractory to these treatments and require further intervention, including shunt occlusion, size reduction, or even emergent liver transplantation. A host of other complications related to TIPS placement include TIPS infection, intraperitoneal hemorrhage, stent stenosis or migration, fistula formation, hemobilia, and sepsis, as well as the dreaded hepatic infarction leading to fulminant liver failure.

Table 20.2 Common Indications for Transjugular Intrahepatic Portosystemic Shunt Recommendation

Current AASLD practice guideline recommends imaging the liver before the TIPS procedure to assess hepatic vascular patency and exclude masses.17 Imaging modalities may include Doppler ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI). Both MRI and ultrasonography are highly accurate for depicting portal venous flow direction, and MRI is more sensitive than Doppler for detecting collateral vessels.¹⁸ In general, Doppler ultrasonography is most commonly used because it is more readily available. In patients with large ascites, the liver may be deeply displaced, complicating Doppler evaluation of hepatic vessels. Difficulty in acoustic penetration secondary to deep location of the vessel of interest ( Fig. 20.1) may lead to a false diagnosis of vascular thrombosis. In these patients, contrast-enhanced CT or MRI is helpful in clarifying equivocal Doppler findings.

Sonographic Terminology

Sonographic terminologies used in TIPS evaluation are standardized mostly based on the direction of blood flow with respect to a reference structure. Hepatofugal flow describes flow away from the liver, and hepatopedal flow describes blood flow toward the liver. Antegrade flow is a term used for the direction of blood flow under normal physiologic conditions. Conversely, retrograde flow is in the opposite direction as antegrade flow. TIPS stents are evaluated in their proximal, mid, and distal segments. The proximal segment is the portion closest to the portal vein (PV). The distal segment is the portion closest to the hepatic vein. Again, these terminologies are with respect to the expected blood flow direction through a properly functioning stent shunting blood from portal to systemic circulation.

Fig. 20.1 Pseudothrombosis of the main portal vein (PV) secondary to its deep location. (a) Routine liver Doppler evaluation before the transjugular intrahepatic portosystemic shunt (TIPS) procedure showing a lack of flow in the main PV. (b) Computed tomography performed later the same day definitively demonstrated opacification of the main PV (red arrow).

Fig. 20.2 Illustration showing the expected transjugular intrahepatic portosystemic shunt stent position bridging the right portal vein (RPV) and the right hepatic vein (RHV). IVC: inferior vena cava; LHV: left hepatic vein; LPV: left portal vein; MHV: middle hepatic vein; MPV: main portal vein. (Used with permission from Patel N, ed. SCVIR Syllabus: Portal Hypertension: Diagnosis & Interventions, 2nd ed. Fairfax, VA: Society of Interventional Radiology; 2001: ©SIR, 2001. All rights reserved.)

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