You are in: eMedicine Specialties > Radiology > GASTROINTESTINAL Portal Vein ThrombosisArticle Last Updated: Mar 22, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Ali Nawaz Khan, MBBS, LRCP, FRCS, FRCP, FRCR, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the USA, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Sumaira Macdonald, MBChB, MRCP, FRCR, PhD, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Aali J Sheen, MBChB, FRCS, Specialist Registrar, Department of HPB Surgery, Manchester Royal Infirmary Oxford Road Manchester UK; Chi-Leung (Eddie) Tam, MD, Consulting Staff, Department of Radiology, Lancaster Royal Infirmary; David Sherlock, MBBS, FRCS, Consulting Staff, Department of Surgery, North Manchester General Hospital, Christie Hospital; Yousif Al-Khattab, MBChB, DMRD, FRCR, Consulting Staff, Department of Radiology, North Manchester Healthcare Trust, UK Editors: Eric P Weinberg, MD, Associate Professor, Department of Radiology, University of Rochester Medical Center, Strong Memorial Hospital; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Arnold C Friedman, MD, FACR, Professor, Department of Radiology, University of Florida Professor of Radiology, Department of Radiology, Shands-Jacksonville Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Kyung J Cho, MD, FACR, William Martel Professor of Radiology, Fellowship Program Director, Department of Radiology, Division of Interventional Radiology, University of Michigan Medical School Author and Editor Disclosure Synonyms and related keywords: PVT, portal venous thrombosis, transient portal vein thrombosis, cavernous transformation of the portal vein INTRODUCTIONSection 2 of 11
  BackgroundPortal vein thrombosis (PVT) is being recognized with increasing frequency with the use of ultrasonography. Reduced portal blood flow due to hepatic parenchymal disease and abdominal sepsis (ie, infectious or ascending thrombophlebitis) are the major causes. Transient PVT is also being recognized with increasing frequency, partly because of the great increase in the use of ultrasonography in the evaluation of patients with abdominal inflammation such as appendicitis. Hypercoagulable syndromes can lead to portomesenteric and splenic vein thrombosis. Patients with these conditions may present with acute or subacute intestinal angina. In late stages, patients can have variceal bleeding. PathophysiologyCavernous transformation of the portal vein (ie, the development of periportal collaterals) occurs with long-standing PVT due to the development of multiple small vessels in and around the recanalizing or occluded main portal vein. A leash of fine or markedly enlarged serpiginous vessels is seen in place of the portal vein. The application of color and/or pulsed Doppler imaging shows blood flow in these periportal collaterals that form around the thrombosed portal vein or that replace the vein. The time-averaged mean velocity of blood flow in the recanalizing portal vein is usually 2-7 cm/s. Cavernous transformation of the portal vein is reported as having the appearance of a subhepatic spongelike mass. This appearance has also been reported in cases of pancreatic hemangiosarcoma. Bile duct varices, also called the pseudocholangiocarcinoma sign, are occasionally observed with endoscopic retrograde cholangiopancreatography (ERCP) in patients with portal hypertension; this finding results from cavernous transformation of the portal vein. This finding is reported to disappear after a transjugular intrahepatic portosystemic shunt (TIPS) procedure when the portal hypertension is reduced. PVT occurs secondary to infection, surgical intervention, or abdominal malignancy (eg, pancreatic or hepatocellular carcinoma) or as a result of liver dysfunction. PVT is a known complication of pyogenic cholangitis. Causes of PVT include the following:
FrequencyUnited StatesThe exact frequency of PVT is not known, but segmental or global PVT occurs in as many as 30% patients with hepatocellular carcinoma. The incidence of PVT in patients with cirrhosis and portal hypertension is approximately 5%. Mortality/MorbidityMorbidity and mortality are related to the underlying disease that is exacerbated by PVT.
AgePVT predominantly affects young children, but it can occur in persons of any age. AnatomyThe portal vein forms behind the neck of the pancreas with the union of the splenic and superior mesenteric veins. It courses to the porta hepatis in the free edge of the lesser omentum and receives the cystic, pyloric, accessory pancreatic, superior pancreaticoduodenal, and other veins that are too small to visualize. Generally, the portal vein enters the porta hepatis and divides into the right and left main branches. The right main branch divides into anterior and posterior branches that supply the anterior and posterior segments of the right lobe. The left main branch courses horizontally to the left before turning vertically to form the medial and lateral segmental branches. Several variations of the portal venous anatomy have been described by using ultrasonography, CT, and cadaveric dissection. Anatomic variants are possible. The normal origin of the left main portal vein branch and the horizontal part of the left main portal vein can be absent. A branch of the right anterior portal vein radical supplies the left lobe of liver. The right main portal trunk can also be absent. Immediately after it enters the porta hepatis, the portal vein turns to the left without resulting in any of the normal right portal vein branches. The right hepatic lobe is smaller than usual, and small veins of varying sizes supply it. The right main portal vein trunk can be absent while its branches are present. Branches of the anterior and posterior right portal veins arise by means of trifurcation of the main portal vein trunk. The right posterior portal vein branch can arises from the main portal vein trunk. The main portal vein then continues into the liver and bifurcates. Clinical DetailsPVT is often not discovered until gastrointestinal hemorrhage develops, unless the thrombosis is discovered during routine surveillance for a known underlying pathologic condition. In most patients, PVT occurs slowly and silently. The signs and symptoms of PVT can be subtle or nonspecific, and they can be overshadowed by those of the underlying illness. The radiologist may be the first physician to suggest the diagnosis on the basis of imaging findings. The exceptions to this scenario are patients with hypercoagulation and portal and mesenteric venous thromboses who present with moderate or severe abdominal pain after acute or subacute development of the thrombosis. Patients may present with abdominal pain; portal systemic encephalopathy; or gastrointestinal hemorrhage due to esophageal varices, splenomegaly, and/or ascites. Symptoms of the underlying cause of the PVT, such as acute pancreatitis, intra-abdominal sepsis, or ascending cholangitis, may predominate. Preferred ExaminationPreferred examinations include duplex Doppler ultrasonography and/or color Doppler ultrasonography, CT, magnetic resonance angiography (MRA), and arterial portography or splenoportography. Tumor in the portal vein may have an appearance identical to that of thrombosis, but this appearance is far less common than others. Tumor in the portal vein is most frequently related to hepatocellular carcinoma. The thrombus may be partial or complete. It may be mixed with bland thrombus as well. Adults who have acute PVT secondary to abdominal sepsis may completely recover, and the vessel may recanalize with successful treatment of the underlying sepsis. In children, the portal vein may recanalize with the development of multiple, small, collateral channels. These channels are seen as a partly echogenic band of small vessels extending to the porta hepatis (cavernous transformation). These have a reduced flow velocity of 2-7 cm/s. Nonvisualization of the portal vein is strongly suggestive of occlusion. The portal vein may then be seen as a band of high-level echoes at the porta hepatis. DIFFERENTIALSSection 3 of 11
Portal Hypertension RADIOGRAPHSection 4 of 11
FindingsPlain radiographs may reveal hepatosplenomegaly, an enlarged azygos vein, and paraspinal varices. Esophageal varices that consist of dilated submucosal veins in the lower esophagus occur chiefly as a consequence of portal hypertension, mostly in cirrhosis. The varices appear as beaded or serpiginous translucent filling defects. Large esophageal varices are obvious and appear as nodular or vermiform, changeable, filling defects within the esophagus. Smaller varices appear as scalloped esophageal folds, which are better seen on recumbent radiographs, because they tend to disappear on upright images. CT SCANSection 5 of 11
FindingsThe portal vein supplies 75% of the blood flow to the liver. Therefore, peak liver contrast enhancement occurs during the portal venous phase, about 60 seconds after the start of a bolus injection of contrast material. With helical CT, a liver examination requires about 20 seconds to complete, and images can usually be acquired in one breath hold. This technique can be extended to acquire a dual-phase contrast-enhanced CT scan for which the liver is imaged twice with a single contrast agent bolus, first during the arterial phase and then through portal venous phase. Dual-phase CT is indicated in some benign and malignant lesions in which vascular characteristics may suggest the correct diagnosis. Angiographically assisted CT, or CT arterial portography, can provide better delineation of the portal venous system and portal venous enhancement of the liver. An angiographic catheter is placed in the common celiac axis, hepatic artery, or superior mesenteric artery by using a modified Seldinger technique via the femoral artery. Image acquisition begins 3-5 seconds after the contrast agent injection is initiated. The examination should be completed as soon as possible, before the contrast material recirculates. To prevent significant artifacts related to the density of the contrast material, 70 mL of dilute (1-30%) iodinated contrast agent is used with an infusion rate of 2 mL/s. Although angiographically assisted CT can produce elegant images, it is invasive, expensive, and not widely accepted. On contrast-enhanced CT scans, PVT may be depicted as a low-attenuating center in the portal vein surrounded by peripheral enhancement. Portal vein attenuation is 20-30 HU less than that of the aorta. CT angiography (CTA) is an application of helical CT. The rapidity of helical CT allows the maintenance of a higher concentration of intravenous contrast medium, particularly through the arterial enhancement phase, and it has the capability of 3-dimensional (3D) reconstruction. Both peripheral intravenous injections of contrast agent and CT arterial portography have been used as with CTA. CTA has shown great promise in the evaluation of hepatic vessels before liver resection. It provides preoperative surgical information about the segmental location of liver tumors, the segmental venous anatomy, and the presence of significant arterial anomalies. The value of CTA in the evaluation of portal hypertension is unclear, but CTA is likely to be useful because it may delineate the collateral vessels, varices, and other findings in patients with portal hypertension. MRISection 6 of 11
FindingsThe vascular anatomy of the liver may be outlined by using spin-echo and gradient-recalled-echo (GRE) techniques, but these techniques cannot demonstrate the direction of portal flow. Time-of-flight MRI with bolus tracking has been successful in the assessment of portal hypertension and its sequelae. Phase-contrast sequences can also be used to evaluate the portal vein, and phase-contrast cine MR angiography can show the direction of portal venous flow and the presence of portal vein thrombus. Magnetic resonance evaluation of the portal venous system is accurate in demonstrating thrombosis and the collateral circulation. Gadolinium enhancement is useful in this application. Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. ULTRASOUNDSection 7 of 11
FindingsPVT is being recognized with increasing frequency at ultrasonography. Reduced portal blood flow due to hepatic parenchymal disease and abdominal sepsis are the major causes. Transient PVT is also being recognized with increasing frequency, partly because of the great increase in the use of ultrasonography in the evaluation of patients with abdominal inflammation such as appendicitis. Tumor in the portal vein may have an appearance identical to that of thrombosis, but this appearance is far less common than others. On sonograms, echogenic lesions may be present in the portal vein. Clot with variable echogenicity may be depicted. The clot usually has moderate echogenicity, but if it is recently formed, it may be hypoechoic. Patent vessels may have increased intraluminal echogenicity because of erythrocyte rouleaux formation, which makes slow-flowing blood slightly echogenic. Increased or decreased echogenicity may be observed in the lumen of portal vein. In isolation, this finding is not sufficient to diagnose or exclude PVT. PVT eliminates the usual venous flow signal from the lumen of the portal vein during either pulsed or color flow Doppler imaging. Color flow Doppler images can show flow around a thrombus that partially blocks the vein. However, if flow is sluggish, the Doppler signal may not be detected. Color flow may be present in other small collateral vessels. Incomplete occlusion may occur. This is common with neoplastic invasion. Alternatively, thrombolytic recanalization may occur. The 2 cannot be differentiated on sonograms. Cavernous malformation, spontaneous shunts, splenorenal and portosystemic collaterals, may be seen. The underlying cause (eg, hepatocellular carcinoma, metastases, cirrhosis, pancreatic neoplasms) may be evident. The incidence of PVT is reported to be low in portal hypertension. The string sign, that is, thickening of the portal vein with narrowing of its lumen, is assumed to be due to portal phlebitis. This is considered a precursor of PVT in patients with acute pancreatitis. The portal vein thrombus may be calcified. The diameter of the portal vein is larger than 15 mm in 38% of the cases of PVT. ANGIOGRAPHYSection 8 of 11
FindingsAmong catheter-directed techniques, arterial portography is now the preferred method for evaluating the portal venous system because it is less invasive and has a lower complication rate than the other methods (eg, splenoportography). The method involves the indirect opacification of the portal venous system with an injection of contrast material into the splenic vein to outline the splenic and portal veins or superior artery to outline the superior mesenteric and portal veins. The 3 major indications for arterial portography are the following: (1) to examine patients with portal hypertension and its sequelae, particularly when surgical treatment is planned; (2) to determine the resectability of hepatic and pancreatic tumors when both the arterial- and venous-phase angiographic findings make a significant contribution; and (3) to perform transcatheter embolization, in cases of metastases of islet cell tumors or carcinoid metastases, or chemoembolization, in cases of hepatocellular carcinoma. (A widely or partly patent portal vein is a prerequisite for such treatment.) Patient preparation and contraindications are the same as those of standard conventional angiography. Selective catheters are used to cannulate the appropriate vessel. In a superior mesenteric artery injection, the tip of the catheter is placed to enable opacification of all the branches with contrast material. Before the delivery of the contrast agent, a vasodilator (Tolazoline, papaverine, Priscoline, or prostaglandin E) is administered to improve opacification of the portal vein. Manual or digital subtraction is necessary. If digital subtraction is used, the administration of an anticholinergic drug (eg, glucagon) prior to imaging reduces bowel motion. Selective injection of the superior mesenteric artery can be used to outline the superior mesenteric and portal veins. For splenic and/or portal vein delineation, splenic artery catheterization is chosen. Injection of the left gastric artery consistently demonstrates esophageal varices. For details about splenoportography, see Portal Hypertension. Another technique for opacifying the portal system is wedged hepatic venous injections of carbon dioxide. The low viscosity of the gas allows it to readily float across the hepatic sinusoids, successfully opacifying the portal vein in most cases. See Carbon Dioxide Angiography for details and images. Degree of ConfidenceDiagnostic modalities such as ultrasonography, CT, and MRI have reduced the diagnostic importance of arteriography in the diagnosis of liver tumors. The role of liver angiography seems to be limited to the occasional mapping the vascular anatomy prior to surgery (now largely performed with MRA or CTA) and the transcatheter treatment of liver tumors. Venous-phase imaging in the celiac axis and superior angiography provides sufficient detail to make direct portography unnecessary in most cases. INTERVENTIONSection 9 of 11
The development of PVT can precipitate the need for emergency endoscopy for sclerotherapy of varices, TIPS creation, surgical portocaval shunt creation, transjugular or transhepatic portomesenteric thrombolysis and thrombectomy, or even resection of ischemic bowel or liver transplantation. However, PVT may complicate sclerotherapy. Fine-needle aspiration biopsy of PVT can be performed with color Doppler sonographic guidance to assess therapeutic effectiveness. Early complications of TIPS creation that are detectable with ultrasonography include the following: intraperitoneal hemorrhage, shunt thrombosis, neck hematoma, compromise of hepatic blood supply, PVT, hepatic artery occlusion, hepatic infarction, failed stent deployment, inadequate stent expansion, stent retraction, stent fracture, andbiliary obstruction. Delayed complications of TIPS creation that are detectable with ultrasonography include the following: shunt stenosis due to pseudointimal hyperplasia and hepatic vein stenosis. Medical/Legal Pitfalls
MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Portal Vein Thrombosis excerpt Article Last Updated: Mar 22, 2007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
