Figure 1-2: Post-contrast image shows heterogeneous enhancement of the liver with caudate lobe hypertrophy. The slit-like IVC is compressed by the liver parenchyma but is patent. Hepatic veins are not identified and are likely thrombosed.

Figure 3: Post-contrast image demonstrates thrombosis of the portal vein (dark band on image).

Figure 4: Post-contrast image demonstrates a patent SMA. The SMV is thrombosed and enlarged. The splenic vein is also thrombosed.

Budd-Chiari syndrome.

Budd Chiari syndrome (BCS) is occlusion of the hepatic veins secondary to an obstruction of the IVC by a membrane or thrombus, or occlusion of the major hepatic venous branches usually by thrombus. Etiologies include:

• Idiopathic
• Congenital: webs, diaphragm, or interruption of the IVC
• Venous thrombosis secondary to hypercoagulabe states: SLE, pregnancy, oral contraceptives, sickle cell disease, paroxysmal nocturnal hemoglobinuria, antiphospholipid syndrome
• Injury or inflammation: phlebitis, autoimmune disease (Behçet disease), trauma, radiation injury, immunosuppressive drugs
• Liver pathology: fibrosis, hemorrhage, congestion
• Tumor: hepatocellular carcinoma (most common), renal cell carcinoma, adrenal carcinoma, metastasis, and leiomyosarcoma of the IVC

Obstruction of the venous outflow from the liver results in portal hypertension, ascites, and progressive hepatic failure. BCS often results in atrophy of the peripheral liver, secondary to severe venous obstruction and hypertrophy of the caudate lobe and central liver, which are relatively spared. The relative preservation or hypertrophy of the caudate lobe is due to the separate veins that drain directly from the caudate into the IVC. Pathologically, acute changes after hepatic vein thrombosis show dilatation of veins and congestion of sinusoids. With progression of disease, the hepatocytes become atrophic with resulting loss of hepatic parenchyma. Two other entities that have similar clinical characteristics are severe right-sided heart failure and veno-occlusive disease of the liver. Hepatic veno-occlusive disease is characterized by inflammation of the post-sinusoidal venules, which results in fibrosis and venous occlusion.

MRI findings in BCS can demonstrate regional differences in signal intensity because of varying perfusion, atrophy, hypertrophy, necrosis, and differences in the amount of intracellular fat or iron. The pre- and post-contrast MRI images of liver can differ for acute and chronic forms of BCS. In acute BCS, the peripheral liver will often show high signal intensity on T2-weighted images and low signal intensity on T1-weighted images, whereas the caudate and central liver will demonstrate normal signal intensity. This is presumably because of the acute increased tissue pressure and edema, with resultant diminished blood supply from both hepatic arterial and portal venous systems. On the post-contrast images, a congested peripheral liver will demonstrate decreased or heterogeneous enhancement in contrast to the increased enhancement of the caudate lobe and central liver. This variable and heterogeneous appearance of the peripheral liver following contrast enhancement can be mistaken for extensive tumor involvement.

In chronic cases of BCS, where parenchymal fibrosis and not edema is the prominent feature, pre-contrast images demonstrate decreased signal of the peripheral liver on both T1- and T2-weighted sequences. The post-contrast enhancement differences between the peripheral and central liver become more subtle in this chronic stage. In patients with long-standing disease, hepatic venous obstruction produces hepatic ischemia which may result in the development of nodular regenerative hyperplasia. Nodules are usually round and of variable size and have increased signal intensity on T1-weighted images and low to intermediate signal intensity on T2-weighted images. These nodules enhance intensely on immediate post-gadolinium images.

Other standard MRI findings include hepatic vein thrombosis, hepatic venous occlusion and narrowing, hepatomegaly, atrophy of the right lobe of the liver, and enlargement of the caudate lobe. IVC abnormalities include diffuse narrowing or focal thrombosis. Venous collaterals, ascites, and thickening of the gallbladder wall and signs of portal hypertension may also be present. MRA techniques are helpful in assessing vascular patency and may be used to identify the direction of flow in the hepatic vessels.

References:

1. Grainger R.G., Allison D., Adam A., Dixon AK (eds). Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging, 4th Ed. London: Churchill Livingstone Inc., c2001. pp. 1266-1267.
2. Semelka RC. Abdominal-Pelvic MRI. New York: Wiley-Liss Inc, c2002. pp. 264-266.
3. Khan AN, Chandramohan M, and MacDonald S. Budd-Chiari Syndrome. (2003). eMedicine.