Applied Radiology

Dr. Assi is a fellow in Vascular and Interventional Radiology in the Department of Radiology, University of Michigan Medical Center, Ann Arbor, MI. He received his MD from American University of Beirut in 1994 and completed his residency at the University of Michigan Medical Center. Dr. Cho is the William Martel Professor of Radiology, at the University of Michigan Medical School.

Major advances in the percutaneous management of hepatoportal venous disease and portal hypertension have been introduced in the past decade. These include catheter-directed thrombolysis, mechanical thrombectomy, embolization, recanalization, balloon angioplasty (percutaneous transluminal angioplasty [PTA]), stent placement, and transjugular intrahepatic portosystemic shunt (TIPS). TIPS has proved to be a safe and effective interventional radiological procedure for the treatment of acute variceal hemorrhage that is unresponsive to sclerotherapy, intractable ascites, and Budd-Chiari syndrome. In addition, it has largely replaced surgical shunt procedures. Recanalization and stenting can relieve hepatic outflow obstruction effectively in patients with Budd-Chiari syndrome. The transhepatic or transjugular approach allows for a variety of percutaneous radiologic interventions for occlusive portal vein diseases, including acute and chronic portal vein thrombosis and portal vein stenosis. The interventional radiologist has played a major role in developing and advancing techniques that have the potential to replace many of the traditional medical and surgical treatments for a variety of occlusive disorders in the hepatic and portal veins and inferior vena cava.

The interventional radiologist plays a major role in the evaluation and management of the diseases involving the hepatic and portal veins. Using a multitude of minimally invasive procedures, the interventional radiologist is able to evaluate the hepatoportal vasculature and better characterize the disease process. A variety of radiologic interventional techniques has been introduced in the management of the patients with hepatoportal venous diseases. The basic methods in current use include embolization, thrombolysis, mechanical thrombectomy, balloon angioplasty, recanalization, stenting, and transjugular intrahepatic portosystemic shunt (TIPS). Choosing an appropriate technique for lesions in the portal and hepatic veins requires proper clinical evaluation, noninvasive imaging studies, and diagnostic angiography. This paper reviews the anatomy, angiography, and major advances in the percutaneous management of patients with hepatoportal venous diseases.

Hepatoportal anatomy

Splenic vein

The splenic vein commences with the 5 to 6 branches originating from the spleen. As the splenic vein courses along the posterosuperior part of the pancreas, it receives numerous short tributaries and joins the superior mesenteric vein behind the neck of the pancreas. The tributaries of the splenic vein are the short gastric veins, the pancreatic veins, the left gastric vein, and the inferior mesenteric vein. In the presence of portal hypertension, portosystemic collaterals develop between the splenic vein and the left renal vein. The inferior mesenteric vein drains blood from the left colic, sigmoidal, and superior hemorrhoidal veins. The latter anastomoses with the middle and inferior hemorrhoidal veins of the hypogastric veins.

Superior mesenteric vein

The superior mesenteric vein is second in size to the portal vein. It drains blood from the veins of the small intestine, the cecum, and the ascending and transverse colon. Its tributaries are the jejunal veins, the ileal veins, the middle colic vein, the ileocolic vein, the right colic vein, and the gastrocolic trunk (GCT). The GCT enters the right side of the distal superior mesenteric vein, carrying blood from the gastroepiploic vein, the colic vein, and the pancreatic arcade veins.

Portal vein

The valveless portal vein is an afferent nutrient vessel of the liver and, therefore, should be considered an arterial vessel. It carries blood from the entire digestive tract (stomach, duodenum, small intestines, and colon), the spleen, pancreas, omentum, and gallbladder. The tributaries of the portal vein are the splenic vein, the inferior mesenteric vein, the superior mesenteric vein, the coronary vein, the pancreatic vein, the pyloric vein, and the cystic veins.

The portal vein commences with the junction of the splenic vein and superior mesenteric vein behind the neck of the pancreas. It courses in the hepatoduodenal ligament dorsal to the bile duct and the hepatic artery. The main portal vein divides into the right and left portal radicles. The right portal vein divides into the posterior and anterior segmental branches; each subdivides into the superior and inferior subsegmental branches. The left portal vein divides into the caudate medial and lateral segmental branches. Each hepatic segment receives its exclusive blood supply. There is no communication between the large portal venous branches. Table 1 shows the measurement of the portal vein and its branches. ¹ This information can be used as reference for proper balloon and stent sizing in the treatment of occlusive lesions in the splenic, superior mesenteric, and portal veins.

Hepatic veins

The central hepatic veins course posteromedially, and empty into the inferior vena cava. The coronary ligament covers them. With some variations, there are three main hepatic veins--the right hepatic vein, the middle hepatic vein, and the left hepatic vein. The left hepatic vein drains the left lobe, which is composed of two major radicles. The middle hepatic vein carries blood from the areas supplied by the right and left portal veins. It sometimes joins the left hepatic vein before emptying into the inferior vena cava. The right hepatic vein drains the right hepatic lobe. Several smaller accessory hepatic veins empty into the vena cava below the main hepatic veins. There are free anastomoses among the various tributaries of the hepatic veins, providing collaterals in the presence of localized hepatic vein occlusion.

Hepatic blood flow

A fifth of the cardiac output of blood passes through the liver sinusoids each minute via the hepatic artery and portal vein. It has been estimated that two-thirds of total hepatic blood flow comes from the portal vein. ² The role of hepatic arterial circulation has not been considered to be vital to the function of the hepatic parenchyma. It supplies the bile duct, connective tissue, and gallbladder, as well as the hepatic sinusoids. The hepatic arterial and portal venous blood mixes in the parenchyma and leaves the liver by way of the hepatic veins. The hepatic artery and the portal vein have a reciprocal interaction; the hepatic arterial flow increases in a variety of conditions that result in reduced portal vein flow, including the following: cirrhosis and portal hypertension, hemorrhage after a side-to-side portacaval shunt, and creation of TIPS.

Portal hypertension

From a hemodynamic point of view, the common trait in hepatoportal diseases is a progressive increase in resistance to portal vein blood flow, resulting in portal hypertension. Diseases can occur before blood enters the liver (presinusoidal), in the liver itself (sinusoidal), and after it leaves the liver (postsinusoidal) (Table 2). Obstruction at any level will lead to the development of portosystemic collaterals and gastrointestinal hemorrhage.

Normal portal vein pressure is 5 to 10 mm Hg. Portal hypertension is defined as portal venous pressure >11 mm Hg or a portosystemic gradient >6 mm Hg. ² Usually, it becomes clinically significant when the gradient is >11 mm Hg. ³ Clinically, patients may present with bleeding gastroesophageal varices or recurrent ascites.

Prehepatic (presinusoidal) portal hypertension -- Presinusoidal portal hypertension has multiple etiologies. It can manifest by increased superior mesenteric and inferior mesenteric vein pressures with normal intrahepatic portal pressure. In this case, a transhepatic portal vein catheterization is preferred to facilitate recanalization of a chronically occluded portal vein using balloon angioplasty or stent placement.

Hepatic (sinusoidal) portal hypertension --Sinusoidal portal hypertension is usually caused by liver cirrhosis, which is the end stage of many forms of liver injury characterized by fibrosis. In the United States, cirrhosis is a major cause of death in people between the ages of 45 to 65 years. Most cases of cirrhosis are due to alcohol abuse, but other etiologies include viral infection, toxin, altered immune response, biliary obstruction, as well as metabolic and congenital causes.

Posthepatic portal hypertension -- This group includes 3 main diseases: veno-occlusive disease (VOD) of the liver, Budd-Chiari syndrome, and hepatic venous or vena caval webs. In the early stage of VOD, microscopic changes include subendothelial edema of the hepatic venules, endothelial cell damage, and microthrombosis. Later features include sclerosis of the venular walls and intense collagen deposition in the sinusoids resulting in hepatocyte necrosis. ^4,5

Portal hypertension caused by increased flow -- Portal hypertension can develop when portal flow is increased (eg, with arterioportal fistula, pancreatic arteriovenous malformations, or massive splenomegaly). This entity is also known as hyperkinetic portal hypertension. A cure can be achieved by eliminating the source of increased portal flow by either surgical intervention or transcatheter embolization.

Hepatoportal diseases

Vessels of the liver may be involved by a variety of systemic or primary diseases. In addition, intrahepatic vessels may be affected in parenchymal liver disease, such as alcoholic liver disease, viral hepatitis, and idiopathic portal hypertension. The effects of hepatic or portal venous disease depend on the level of occlusion, the type of vessel involved, and whether the occlusion is acute or chronic.

Lesions of the portal vein and its branches

Acute portal vein occlusion --Portomesenteric venous thrombosis is an uncommon cause of mesenteric ischemia. Conditions associated with mesenteric venous thrombosis include hypercoagulable states, portal hypertension, intra-abdominal inflammation, and postoperative state or trauma. Unlike mesenteric ischemia caused by arterial occlusion, mesenteric venous thrombosis causes less distinct demarcation. Sudden occlusion of the portal vein or its branches can lead to true infarction in the liver, so-called infarct of Zahn. ⁶ The natural history and outcome of portomesenteric venous thrombosis are not well known. The clinical presentation depends on the extent of thrombosis and the presence of collateral vessels; it can be as devastating as ischemic intestinal necrosis or remain unnoticed until cavernomatous transformation develops and bleeding from portal hypertension brings the patient to clinical attention. Portal vein occlusion occurs in a variety of conditions including cirrhosis, shunt surgery for portal hypertension, trauma, omphalitis, TIPS, coronary embolization, and involvement by primary
neoplasm (hepatoma, cholangiocarcinoma, or pancreatic adenocarcinoma). ^7-11 The inciting factors in trauma, stagnant circulation, and malignancy are likely to be endothelial damage and blood hypercoagulability.

Chronic portal vein occlusion -- When portal vein thrombosis becomes chronic, numerous collateral channels develop. They originate from the superior mesenteric vein and ascend along the hepatoduodenal ligament in the venous phase of the superior mesenteric angiogram. This is known as cavernomatous transformation of the portal vein . This term was originally described as a pathologic condition of the portal vein and lesser omentum that gives a sponge-like appearance. ¹¹ This, in fact, is caused by numerous fine collateral blood channels in the presence of portal vein occlusion, rather than representing cavernomatous transformation of the portal vein.

Chronic mesenteric vein thrombosis -- In chronic mesenteric vein thrombosis, numerous small collateral veins appear throughout the mesentery without filling the superior mesenteric vein in the venous phase of the superior mesenteric angiogram. If the portal vein is occluded, the intrahepatic portal branches may reconstitute by peribiliary venous collaterals.

Neoplastic portal vein occlusion --Neoplasms shown to occlude the portal vein include hepatocellular carcinoma, cholangiocarcinoma, and pancreatic tumors. Angiographically, the involved veins show localized narrowing or occlusion, and portal vein invasion by hepatocellular carcinoma shows characteristic fine, linear abnormal vessels coursing the portal vein radicles.

Pylephlebitis --Portal vein phlebitis may occur with or without associated thrombosis, usually resulting from intra-abdominal suppuration, such as intra-abdominal abscess, appendicitis, or colonic diverticulitis. In newborn infants, it can result from acute omphalitis or umbilical vein catheterization.

Hepatoportal sclerosis --Hepatoportal sclerosis is an important cause of noncirrhotic (idiopathic) portal hypertension. It affects the intrahepatic portal vein branches, resulting in periportal and lobular fibrosis.

Splenic vein occlusion --The causes of splenic vein occlusion include pancreatitis, pancreatic tumors, and peripancreatic or retroperitoneal neoplasm. Splenic vein occlusion can cause hypersplenism and gastric bleeding from gastric varices. ^12,13 Imaging findings, which suggest splenic vein occlusion, are gastric varices without esophageal varices and collateral veins in the left upper abdomen. The diagnosis is confirmed by celiac or splenic angiography, which shows the short gastric (left gastric, left gastroepiploic), right gastroepiploic, and omental venous collaterals.

Lesions of the hepatic outflow tract

Lesions of the hepatic venous outflow tract may involve the intrahepatic or central hepatic veins, or the hepatic portion of the inferior vena cava. Disease of the hepatic veins may be primary or associated with a systemic disease, neoplasm, or surgical procedure.

Hepatic VOD --Veno-occlusive disease is a clinical syndrome seen in patients who consume herbal teas and in 10% to 60% of patients receiving bone marrow transplants. ¹⁴ Liver enlargement, pain, jaundice, and ascites characterize the syndrome. Patients with mild to moderate disease usually recover with medical therapy alone; in contrast, severe disease often results in multiorgan failure and death. ⁵

The Budd-Chiari syndrome --Hepatic vein occlusion (the Budd-Chiari syndrome) is an uncommon cause of portal hypertension and hepatic failure. It is characterized by hepatic venous and/or inferior vena cava outflow obstruction. The most common etiology worldwide is membranous obstruction of the hepatic veins or inferior vena cava. In the United States, hepatic vein or inferior vena cava thrombosis is the usual cause. Predisposing factors include polycythemia vera, paroxysmal nocturnal hemoglobinuria, systemic lupus erythematosus, idiopathic thrombocytopenia, oral contraceptive use, pregnancy, myeloproliferative disease, Behçet's disease, hypercoagulable state, and it can also occur idiopathically. ¹⁵ The majority of patients present with massive ascites as well as tender and enlarged livers.

Ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) have been used in patients with suspected Budd-Chiari syndrome. MRI is an excellent imaging modality for evaluating these patients and can offer vascular information necessary for intervention. Like CT, MRI can depict hepatomegaly, inhomogeneous liver enhancement, ascites, and occlusion of the hepatic segment of the inferior vena cava by tumor, such as hepatoma or hypernephroma. In addition, it can provide the important
vascular anatomy including the caliber of the hepatic veins and inferior vena cava, and extent of the occlusive disease.

Angiographic studies (arteriography and venography) remain the gold standard for the diagnosis of Budd-Chiari syndrome. Celiac arteriography shows hepatomegaly with an inhomogeneous hepatogram and can exclude neoplasms causing hepatic outflow obstruction. The first angiographic study in a patient with suspected Budd-Chiari syndrome should be an inferior venacavography. It may show occlusion or stenosis of the vena cava at the hepatic level. If the hepatic veins are occluded, no flow defect may be seen on a venacavogram. The hepatic veins should then be catheterized selectively and a wedged hepatic venogram should be performed. This gives the typical appearance, called "spider-web," which represents intrahepatic collateral channels between the hepatic venules and systemic veins. If the main and all accessory hepatic veins are blocked, a 22-gauge needle can be introduced into the liver percutaneously from the right lateral approach, and 20 to 30 mL of carbon dioxide should be injected to fill the hepatic and portal veins as well as the collateral channels. Liver biopsy should be obtained whenever possible because the result is useful in determining treatment options. In the presence of ascites, the liver biopsy can be performed relatively safely using the transjugular approach.

Angiographic methods

Angiography is frequently used for the evaluation of patients with hepatoportal diseases prior to a portosystemic shunt operation and percutaneous hepatic-portal interventions. A number of angiographic techniques are available to evaluate hepatoportal blood flow, vascular anatomy, and underlying lesions. These fall into three major groups: (1) arterial, (2) hepatic venous, and (3) portal venous. Each of these groups gives important information about the hepatoportal vascular anatomy and hemodynamics in patients with cirrhosis, portal hypertension, and hepatoportal venous disease. Selection of the angiographic methods should depend on the underlying disease, intended interventions, and the availability of veins for access.

Arterial studies

The technique generally used for arterial studies is the standard Seldinger technique. The femoral approach is the most preferable. Celiac angiography in the evaluation of patients with hepatoportal disease and portal hypertension is performed to do the following: exclude causes of massive upper gastrointestinal bleeding other than varices, to exclude hepatoma, and to show the portal vein and portosystemic collateral veins. Superior mesenteric and splenic angiography is performed to visualize the patency of the splenic, superior mesenteric, and portal veins. Visualization of the superior mesenteric and portal veins is accomplished by injecting a large volume of contrast medium into the superior mesenteric artery. An intra-arterial injection of a vasodilator, such as tolazoline or nitroglycerine, just before contrast injection enhances portal vein visualization.

Wedged hepatic venography

Wedged hepatic venography is used for the evaluation of cirrhosis, portal hypertension, and other hepatoportal venous diseases. Wedged hepatic venous pressure reflects portal pressure in the absence of presinusoidal block. In cirrhosis, wedged hepatic venous pressure minus right atrial pressure gives a portosystemic gradient, which represents intrahepatic resistance to portal flow. Normal wedged hepatic venous pressure in a patient with esophageal varices indicates that presinusoidal block is the cause of portal hypertension. If the portal blood flow is hepatopetal, the main portal vein will not fill with the injection of contrast medium into a wedge hepatic vein. Carbon dioxide wedged hepatic venography is commonly used to visualize the portal vein since it fills the portal vein even in the presence of hepatopetal portal flow. Wedged hepatic venography can be performed with either the femoral or jugular approach using an end-hole catheter or an occlusion balloon catheter. If the portal vein cannot be visualized with the wedged hepatic injection, carbon dioxide is injected into the liver parenchyma, which usually fills the portal vein.

Transhepatic portal vein catheterization

The transhepatic approach is used for intervention in the portal vein and its branches. The technique is similar to percutaneous transhepatic cholangiography and employs a 22-gauge Chiba needle introduced in the right midaxillary line at the 9th-10th or 10th-11th intercostal space. After dilating the tract, a 5F sheath is placed for portography and pressure measurement. At the end of the procedure, the percutaneous tract can be embolized with Gelfoam (Pharmacia and Upjohn, Inc., Peapack, NJ) pledgets or coils to prevent bleeding from the puncture site. The transhepatic approach is also used for stent placement of the hepatic vein in patients with Budd-Chiari syndrome.

Splenoportography

Splenoportography was developed prior to arterial portography ¹⁶ and is not currently a popular procedure because of its potential complications. An 18-gauge needle is placed in the spleen and iodinated contrast is injected into the splenic pulp to visualize the splenic and portal veins. If the portal flow is reversed, the portal vein may not fill with the splenic injection. Contraindications include coagulopathy and ascites.

Now splenoportography can be performed safely with the injection of carbon dioxide using a 22- or 25-gauge needle introduced into the spleen under ultrasound guidance. The transsplenic approach can be used for catheterization of the splenic and portal veins when the transhepatic or transjugular approach is not feasible. Splenic arterial embolization prior to transsplenic portal vein catheterization reduces bleeding from the spleen. At the end of the procedure, the splenic tract should be occluded with gelatin pledgets or coils.

Interventional methods

A number of interventional methods have been developed by which hepatoportal venous diseases can be treated percutaneously. Commonly used techniques include the following: (1) embolization, (2) thrombolysis, (3) mechanical thrombectomy, (4) venous recanalization, (5) balloon angioplasty, (6) stenting, and (7) TIPS. Selection of the appropriate angiographic and intervention techniques for hepatic-portal interventions should begin with a thorough clinical evaluation. Review of the available noninvasive imaging studies prior to intervention is essential. In most instances, no single angiographic technique is capable of providing all the necessary intervention; a combination of several techniques is usually required. A brief review of each technique and its indications are discussed.

Variceal embolization

The most common site for bleeding varices is in the esophagus. Endoscopic sclerotherapy remains the initial therapeutic treatment for esophageal varices. Approximately 10% to 15% of patients have gastric varices that may not be amenable to endoscopic therapy. Rarely, the variceal bleeding may occur at unusual sites--including the duodenum, ileum, colon, rectum, bladder, or enterostomy or ileostomy stomata.

In 1974 Lunderquist and Vang ¹⁷ first described variceal percutaneous transhepatic embolization (PTE) in patients with cirrhosis and portal hypertension. Percutaneous transhepatic embolization remains a useful option when variceal bleeding recurs following sclerotherapy, or varices in the stomach or at the unusual sites cannot be treated by the endoscopic approach. Variceal embolization is often used when varices continue to fill following creation of TIPS.

Prior to a transhepatic procedure, celiac and superior mesenteric angio-graphies should be performed to exclude a source of upper gastrointestinal bleeding other than variceal bleeding. The portal venous phase of celiac and superior mesenteric angiographies should be evaluated for patency of the portal venous system. A branch of the right portal vein is punctured from the right lateral approach in the midaxillary line midway between the costophrenic angle and inferior angle of the liver using a 22-gauge needle. The needle is withdrawn with injections of small amounts of contrast medium until a portal vein radicle is visualized. After confirmation of the needle in the portal vein, a 0.018-in Cope mandril wire (Cook Inc., Bloomington, IN) is advanced into the portal vein. The needle is then removed, and the portal vein is catheterized using a 3/4 coaxial dilator, a 6F Cope introducer, or Neff percutaneous access set (each product from Cook Inc.).

After a 5F catheter has been introduced into the proximal splenic vein, a splenoportogram is performed to obtain a road map. A 5F Cobra catheter is introduced to embolize varices filled from the splenic vein (Cook Inc., Bloomington, IN). Several embolic materials or agents can be used to control variceal bleeding. These include Gelfoam (Pharmacia & Upjohn, Co., Kalamazoo, MI), absolute alcohol, coil, and glue. The feeding veins and varices should be occluded throughout their course. Although the method is relatively safe and effective in controlling acute variceal bleeding, variceal bleeding usually recurs from new gastric and esophageal varices. Therefore, a portal vein decompression procedure, such as TIPS, is required for long-term control of variceal bleeding. The potential complications of coronary vein embolization include portal/splenic thrombosis, systemic embolization, death, hemoperitoneum, pneumothorax, subcapsular hematoma, and gallbladder puncture.

Balloon angioplasty

Balloon angioplasty has been used to treat focal stenosis of the hepatoportal venous system, webs and membranes of the inferior vena cava, and suprahepatic and infrahepatic stenosis of the inferior vena cava in orthotopic liver transplants. ¹⁵

Stent placement

Balloon angioplasty should be a first-line treatment for stenosis in the hepatic and portal veins as well as the inferior vena cava. Stent placement is indicated in the following conditions: (1) unsuccessful percutaneous transluminal angioplasty (PTA), (2) restenosis following PTA, (3) hepatoportal occlusion, (4) diffuse lesions, (5) extrinsic compression, and (6) inflammation, such as pancreatitis. Stents can maintain patency of large veins effectively, but restenosis ocurrs frequently in small veins due to myointimal hyperplasia. The most commonly used stents in the hepatoportal system are self-expandable stents such as Wallstent (Boston Scientific Corporation, Natick, MA). Large-diameter stents are available for inferior vena cava stenosis, including Wallstent and Cook-Z Stent (Cook Inc.).

Mechanical thrombectomy

Mechanical thrombectomy has become a useful percutaneous method in recanalizing acute thrombosis, particularly when thrombolysis is contraindicated. There are 2 types of mechanical thrombectomy devices available: (1) mechanical devices with external motor-driven, rotating action for thrombofragmentation (products include the Amplatz Thrombectomy/Clot Buster, Microvena, White Bear Lake, MN; and the Arrow-Trerotola Percutaneous Thrombolytic Device, Arrow International, Reading, PA) and (2) hydrodynamic devices that remove clots by the Venturi effect (products include the Hydrolyser catheter, Cordis Endovascular, Warren, NJ; AngioJet Rheolytic Thrombectomy system, Possis Medical, Minneapolis, MN; and the Oasis catheter, Boston Scientific Corp., Natick, MA). Clinical experience with these devices in the portal venous system is limited, and their safety and efficacy are unknown.

Thrombolysis

Thrombolytic agents can be used in the treatment of acute thrombosis of the portal or hepatic veins. ¹⁸ They can be infused intravenously or directly into thrombus. Catheter-directed thrombolysis is safer and more effective than intravenous thrombolysis. Two basic techniques of the catheter-directed lysis are the infusion method and pulse-spray technique. Both methods are used for thrombolysis in the hepatic and portal veins as well as their main branches. The thrombolytic agents that are currently available in the United States are alteplase (Activase, Genentech Inc., San Francisco, CA) and reteplase (Retavase, Centocor, Inc., Malvern, PA). Urokinase (Abbokinase, Abbott Laboratories, Abbott Park, IL) is not available in the United States.

TIPS

TIPS are shunts created percutaneously between the hepatic vein and the portal vein using the jugular vein. TIPS have been shown to be safe and effective in treating patients with esophageal variceal hemorrhage unresponsive to endoscopic scelerotherapy, and intractable ascites. The procedure involves catheterization of the right or middle hepatic vein from the jugular vein. Once the catheter has been wedged in a distal hepatic vein, a carbon dioxide digital subtraction venogram is obtained to identify the location of the portal vein radicle. Once the right portal vein radicle is punctured from the hepatic vein using a Colapinto needle, a guidewire is advanced into the splenic or superior mesenteric vein. After portal vein pressure measurement, a direct portogram is performed. The liver parenchymal tract is dilated to 8 mm using an angioplasty balloon catheter. Then a metallic stent is deployed from the main portal vein through the liver parenchyma to the central hepatic vein. The stent is then dilated to 10 mm in diameter. If the portosystemic gradient has been reduced to <12 mm Hg, the procedure is considered successful and is terminated. The TIPS are then checked for patency using Duplex ultrasound at 24 hours and every 3 months.

Hepatic-portal interventions

Interventions in the portal vein and its branches

Acute portal and mesenteric vein thrombosis -- The natural history and outcomes of portomesenteric venous thrombosis are not well known. Its clinical presentation depends on the extent of thrombosis and the presence of collateral vessels.

Current therapeutic methods for acute portomesenteric thrombosis include anticoagulant therapy, systemic thrombolytic therapy, catheter-directed thrombolysis, and mechanical thrombectomy. Early recognition and treatment of the underlying causes may prevent the development of portal hypertension. ¹⁹ Intravenous thrombolytic therapy has been used in patients with portal vein thrombosis, resulting in symptomatic relief. ²⁰ Now catheter-directed thrombolysis is the standard method of treating both arterial and venous thrombosis. In the hepato-portal venous system, a percutaneous transhepatic or transjugular approach has been used for intrathrombic delivery of lytic agents in patients with mesenteric and portal vein thrombosis. ^21-23 When rapid removal of clots is needed, or when lytic agents cannot be used because of contraindications, use of mechanical thrombectomy devices is a viable option. AngioJet and Fogarty (Edwards Lifesciences, Irvine, CA) catheters have been used for the treatment of portomesenteric thrombosis. Others have also used similar mechanical devices in the portal venous system. ²⁴

Chronic portal vein thrombosis --Chronic portal vein thrombosis with cavernomatous transformation may cause portal hypertension and variceal bleeding. Portal vein thrombosis accounts for about half of the cases of portal hypertension in children. A percutaneous transhepatic or transjugular approach can be used to recanalize chronic portal vein occlusion in both adults and children (Figure 1). In children, sclerotherapy has been effective with reported long-term success rates
>90%. ²⁵ Shunts are indicated in cases of sclerotherapy failures. Cwikiel et al ¹⁰ described a case of an 8-year-old child in whom stent recanalization of the chronically occluded portal vein with cavernomatous transformation was performed successfully. This technique, if successful, has the potential to replace surgical shunts in children.

Stein and Link ²⁶ have reported their experience with recanalization and reconstruction with endovascular stents in 21 patients with symptomatic spleno-mesenteric-portal venous thrombosis. Their indications for the procedure were variceal bleeding, ascites, hypersplenism, and enteropathy. TIPS procedures were performed in 5 cases. The technical success of portal vein reconstruction was 85.7%, and the 30-day mortality rate was 14.3% (mortality was not procedure related). Stein and Link concluded that portal vein reconstruction is safe and effective in treating symptomatic chronic portal vein occlusion.

Transhepatic stent placement has also been used for the treatment of proximal portal vein stenosis associated with pancreatitis, causing recurrent bleeding from duodenopancreatic varices, ²⁷ and mesenteric vein occlusion, causing jejunal variceal bleeding. ²⁸ In patients with cirrhosis complicated by chronic portal vein occlusion with or without cavernomatous transformation, TIPS is performed following portal vein recanalization. ^29­31

Neoplastic portal vein occlusion --Various tumors can cause portal vein narrowing, including hepatocellular carcinoma, pancreatic adenocarcinoma, cholangiocarcinoma, and metastatic neoplasm. If the portal vein involvement causes portal hypertension and bleeding, intraportal stent placement can restore portal blood flow and relieve portal hypertension ³² (Figure 2).

Stenosis of portal anastomosis complicating liver transplantation --Stenosis of the portal vein at the site of anastomosis after liver transplantation is rare, with an incidence of 0.5% to 6.5%. ^33,34 Portal venoplasty is a safe and effective procedure for the treatment of portal hypertension associated with portal vein stenosis arising from complications from liver transplantation in both adults and children. ^34-37 The usual approach is percutaneous transhepatic, although some prefer the transjugular intrahepatic access because of the decreased risk of bleeding. ³⁷ Access to the portal vein is gained by a standard percutaneous transhepatic approach or transjugular approach. After the portal vein has been catheterized, a 6F sheath is introduced into the portal vein. The portal vein stenosis is crossed using a 0.035-in hydrophilic-coated wire and a 5F end-hole catheter is introduced. Once the lesion has been crossed, a 5F pigtail catheter is advanced into the proximal splenic vein, and a pressure gradient across the lesion is obtained. A splenoportogram is then obtained to delineate the portal venous anastomotic stenosis prior to balloon angioplasty. High technical success rates can be achieved, resulting in resolution of portal hypertension. Before withdrawal of the sheath, the liver parenchymal tract should be occluded with gelatin sponge pledgets or coils to prevent bleeding from the hepatic capsular puncture site. After portal venoplasty, follow-up with imaging studies is needed to detect recurrent stenosis. Recurrent stenosis can be treated successfully with repeated balloon angioplasty. Although most portal vein stenosis responds to balloon angioplasty, their long-term efficacy remains unknown.

Splenic vein occlusion --Asymptomatic splenic vein occlusion requires no treatment. When splenic vein occlusion causes gastric variceal bleeding or hypersplenism, splenectomy is usually performed. Standard sclerotherapy is ineffective in treating acute bleeding from gastric varices. ³⁸ If the patient is not a surgical candidate, splenic vein recanalization and stenting may be used as an alternative treatment, but its long-term efficacy is not known. ^26,39

Interventions in the hepatic veins and inferior vena cava

Therapeutic options for hepatic venous outflow obstruction depend on the underlying pathologic process, extent of occlusive lesions, and clinical course. Surgery has played the major role in the treatment of Budd-Chiari syndrome. ⁴⁰ Now percutaneous radiology-guided interventions play a significant role in the treatment of hepatic venous outflow obstruction, and they have replaced many of the surgical procedures, such as surgical construction of portosystemic shunts and resection of membranous webs from the inferior vena cava. Orthotopic liver transplantation remains the preferred treatment when surgical or percutaneous interventions are not feasible or have failed, or when biopsy results show severe progressive hepatic fibrosis with deteriorating liver function.

Hepatic VOD --Based on the pathologic findings of microthrombi and fibrin deposition in VOD, treatments have been aimed at anticoagulation and promoting fibrinolysis. This could be useful early in the disease process. However, once multiorgan failure sets in, the risk of bleeding increases significantly and there is no proven survival benefit. ⁴¹ TIPS has been used as a treatment for VOD. Fried et al ⁴² reported 6 cases of VOD managed with TIPS; 5 of the 6 patients died, 1 patient with less advanced disease survived. Currently, there is no proven beneficial role of TIPS except to manage concomitant portal hypertension and variceal bleeding (Figure 3).

The Budd-Chiari syndrome --The prognosis of untreated patients with Budd-Chiari syndrome is poor; 89% die within 3.5 years of the onset of symptoms. ⁴³ Medical treatment with diuretics and anticoagulants may relieve symptoms but appears to have no significant survival benefit. Thrombolytic therapy is generally considered an effective treatment. Surgery has played the major role in the management of Budd-Chiari syndrome; it can help maintain hepatic function and prevent variceal bleeding. Surgical treatments that have been used include construction of portosystemic shunt, mesoatrial shunt, portoatrial shunt, resection of membranous webs, and orthotopic liver transplantation. ^40,44-46

Because of their demonstrated safety and efficacy, percutaneous interventions have been used with increasing frequency as the preferred alternative to surgery for patients with Budd-Chiari syndrome. These include percutaneous transluminal balloon angioplasty, stent placement, and TIPS. ^47-55 Liver transplantation is the only treatment option for patients with progressive hepatic fibrosis with deteriorating liver function. ^56,57 TIPS has been shown to improve hepatic synthetic dysfunction and resolve ascites, providing an effective bridge to hepatic transplantation for patients with Budd-Chiari syndrome. ^58,59

PTA should be the first intervention for focal stenosis or webs of the hepatic vein and inferior vena cava. ^60,61 The reported mean patency of balloon angioplasty of this lesion is 9.5 months. ^29,48,49,52 For recurrent lesions and lesions unresponsive to angioplasty, stent placement is required. ^50,51,62 Recanalization and stent placement are usually required for treatment of extensive hepatic vein occlusion ⁶³ (Figure 4). Reports in the literature indicate that initial technical success rate is high with 1-year patency rates of 80% to 100%. ⁶⁴ Because frequent restenosis requires repeated PTA, Venbrux ⁶⁴ used self-expandable Z-stents in the severely stenotic inferior vena cava in patients with Budd-Chiari syndrome. Stents of appropriate size should be used to prevent migration of the stent. Self-expandable stents such as Wallstents (12 or 14 mm in diameter) are commonly used for the treatment of central hepatic vein stenosis. The stents should extend to the junction of the hepatic vein and inferior vena cava. Stent protrusion into the suprahepatic inferior vena cava should be avoided, as it may interfere with future hepatic transplantation. The usual stent sizes for vena caval stenosis or occlusion are 15 to 20 mm.

Hepatic venous outflow obstruction complicating liver transplantation --Hepatic venous outflow obstruction can occur as a complication following orthotopic liver transplantation. The level of obstruction can be at the hepatic vein, suprahepatic caval anastomosis, or both hepatic vein and hepatic portion of the inferior vena cava. Stent placement of the right hepatic vein and the inferior vena cava (if necessary) can relieve hepatic venous obstruction effectively and restore donor liver function. ⁶⁵

Suprahepatic caval anastomotic stenosis is a rare complication of hepatic transplantation with reported incidences of 0.8% to 2.5%. ^46,66,67 Caval stenosis may also occur at the infrahepatic anastomosis. ^68,69 Clinical presentations of inferior vena cava stenosis depend on their location and severity. Suprahepatic caval stenosis can cause lower extremity edema, ascites, and hepatic failure. PTA and stent placement have replaced the old surgical treatments such as hepatopexy, thrombectomy, and retransplantation for cava stenosis. PTA has been shown to be an effective treatment for suprahepatic caval anastomotic stenoses. ^70-72 (Figure 5). Recurrent stenosis usually responds favorably to repeated PTA. In reported cases, the time interval between the operation and the percutaneous intervention ranged from 3 weeks to 4.5 years. The balloon sizes used for PTA were 8 to 20 mm in diameter. When obstruction is caused by kinking of the suprahepatic inferior vena cava in the early postoperative period, self-expandable stents should be used to avoid rupture of the anastomosis.

Conclusion

Several fundamental requirements are needed to be able to accurately evaluate and successfully treat the diseases involving the hepatic vasculature. First, understanding the extrahepatic and intrahepatic vascular anatomy and its relationship to other structures within or outside the liver is crucial. Second, familiarity with the noninvasive imaging of the liver such as ultrasound, CT, and MRI is important. Third, knowledge of the pathophysiology and natural history of each disease can prevent unnecessary interventions and make the interventional radiologist's role clinically important. Choosing an appropriate interventional method for hepatoportal occlusive disease should begin with proper clinical evaluation. No single technique is capable of treating complex hepatoportal lesions. Thoughtful selection of current interventional techniques is essential for the safe and effective performance of hepatic-portal interventions. These include angiography, embolization, thrombolysis, mechanical thrombectomy, recanalization, angioplasty, stenting, and TIPS.