This educational poster is divided into two parts, in which we analyzed the common features and the particular characteristics of Budd-Chiari syndrome.

I. Current Imaging Aspects

The imaging appearance of Budd-Chiari syndrome varies based on the disease stage, from acute to chronic.

1. Acute Form (less than a month since disease onset)

In acute BCS, imaging findings correspond to histologic changes of liver congestion and edema [2].

CT Findings:

• Diffuse enlargement with low attenuation due to congestion;
• Peripheral areas show reduced enhancement (due to portal and sinusoidal stasis), while the central parenchyma exhibits greater contrast uptake;
• Thrombotic material may be present within the hepatic veins, indicating vascular obstruction.

MRI Findings:

• Decreased signal on T1-weighted images;
• Heterogeneously increased signal on T2-weighted images, especially in the peripheral region;
• T1 + Gd: The differential increase in contrast between the central and peripheral liver regions results in greater contrast enhancement of the parenchyma adjacent to the inferior vena cava [4, 5].

The enhanced uptake pattern of the central and peripheral liver regions creates a mottled 'nutmeg liver' appearance. Key imaging signs of hepatic venous outflow obstruction include absent or reversed hepatic vein flow, without venous collaterals, features that help differentiate acute from subacute cases. Common associated findings include ascites and congestive splenomegaly, indicating liver dysfunction [1].

Fig 1: An 18-year-old female patient with hereditary thrombophilia and acute Budd-Chiari syndrome. The liver appears inhomogeneous and mottled, demonstrating a 'nutmeg liver' appearance. Thrombi are present in the hepatic veins and inferior vena cava (red arrows). Ascitic fluid is also noted.

Fig 2: A 35-year-old female patient with hereditary thrombophilia and acute Budd-Chiari syndrome, presenting with a 'nutmeg liver' appearance. Thrombosis of the inferior vena cava extending into the right atrium (red arrows) is observed. Ascites is present.

2. Subacute Form (between one and six months since disease onset) 

Imaging Findings: Volume redistribution and collateral vessel formation, these imaging characteristics help differentiate subacute BCS from its acute form [2, 6].

In subacute BCS, intrahepatic and extrahepatic collaterals improve drainage, creating more homogeneous enhancement than in acute BCS. However, persistent congestion and edema indicate ongoing vascular compromise.

Subacute and chronic BCS have overlapping imaging features, but chronic BCS shows less edema, more fibrosis, regenerative nodules, and well-developed collaterals. Clinical history, labs, and imaging follow-up are key for differentiation [4].

Fig 3: A 39-year-old male with chronic myeloproliferative syndrome and subacute Budd-Chiari syndrome. Hepatic congestion with volumetric redistribution of liver lobes. The hepatic veins are thrombosed (red arrows). The liver appears inhomogeneous and mottled, displaying a 'nutmeg liver' appearance, with greater contrast uptake in the central parenchyma. Ascites is present.

Fig 4: A 48-year-old female patient with idiopathic subacute Budd-Chiari syndrome. The liver appears inhomogeneous and mottled, displaying a 'nutmeg liver' appearance. The enhancement pattern becomes more homogeneous on delayed imaging sequences. Thrombosis of the right hepatic vein is observed (red arrows).

3. Chronic Form (more than six months since disease onset)

Imaging Findings: well-developed intrahepatic and subcapsular collaterals, caudate lobe hypertrophy, peripheral atrophy, irregular liver contour, regenerative nodules, and significant liver size reduction. Edema is minimal, with advanced stages showing progressive atrophy due to fibrosis and tissue remodeling.

Chronic BCS shows portal hypertension with portal vein dilation (>13 mm), hepatofugal flow, enlarged mesenteric and splenic veins, paraumbilical vein recanalization, portosystemic collaterals, splenomegaly, and ascites [7].

Chronic BCS may lead to cirrhosis complications like variceal bleeding, hepatic encephalopathy, and hepatocellular carcinoma.

Fig 5: A 42-year-old male patient with idiopathic chronic Budd-Chiari syndrome. The liver appears inhomogeneous and mottled. Hypertrophy of the caudate lobe is present. The left hepatic vein is segmentally patent (red arrow), along with collateral venous outflow pathways (blue arrow). Splenomegaly is observed. Ascitic fluid is present.

Fig 6: A 59-year-old female patient with idiopathic chronic Budd-Chiari syndrome. The liver exhibits a dysmorphic appearance with significant intrahepatic collateral circulation pathways (red arrows). The major hepatic veins are not visible. A tributary vein of the caudate lobe (green arrow) is observed, associated with compensatory hypertrophy of the lobe.

II. Budd-Chiari Syndrome: Particular Imaging Aspects

1. HNF-like regenerative nodules

BCS is characterized by regenerative nodules, typically multiple and variable in size, due to hepatic blood supply imbalance [8]. Insufficient perfusion causes hepatocyte atrophy, while compensatory hyperplasia occurs in areas with preserved arterial inflow. These nodules are primarily supplied by arterial blood, leading to prominent arterial-phase hyperenhancement on imaging [4].

Hepatic regenerative nodules require differentiation from other hypervascular lesions, including hemangiomas, hepatic adenomas, dysplastic nodules, HCC, and metastases. Due to overlapping imaging features, accurate identification is essential to prevent misdiagnosis and mismanagement. Magnetic resonance imaging, particularly the hepatobiliary phase, is critical for diagnosis in BCS, as it highlights similarities with focal nodular hyperplasia (FNH).

Fig 7: A 32-year-old female with chronic myeloproliferative syndrome, chronic Budd-Chiari syndrome, and a transjugular intrahepatic portosystemic shunt (TIPS). Thrombus is present in the hepatic veins and inferior vena cava (red arrows). The liver appears inhomogeneous and mottled, displaying a 'nutmeg liver' appearance. Multiple hypervascular regenerative nodules are noted. Intrahepatic collateral vessels are present (green arrow). Ascitic fluid is observed.

Fig 8: The same patient as in Figure 7. Multiple regenerative nodules appear hyperintense on T1-weighted MR images and are predominantly hypointense relative to the liver on T2-weighted images. The nodules are hypervascular after contrast administration and appear hyperintense in the hepatobiliary phase.

Fig 9: A 52-year-old male with essential thrombocythemia and chronic Budd-Chiari syndrome. Multiple hepatic regenerative nodules exhibiting T1 hyperintensity, T2 isointensity, and arterial-phase hyperenhancement, with a tendency to homogenize in subsequent phases. These nodules appear hyperintense in the hepatobiliary phase.

2. BCS with predominantly lobar involvement of the hepatic parenchyma

The number of hepatic veins that must be occluded to cause clinically significant hemodynamic alterations remains a subject of ongoing debate. A key question is whether the obstruction of a single hepatic vein is sufficient to disrupt hepatic circulation and cause symptomatic disease, or if compensatory mechanisms, such as drainage through the remaining patent hepatic veins, mitigate significant hemodynamic consequences [9].

BCS diagnosis relies on clinical, biological, and imaging findings. Symptoms usually occur when at least two of the three hepatic veins are occluded, leading to severe hepatic congestion and portal hypertension.

Fig 10: A 52-year-old male with multiple myeloma and Budd-Chiari syndrome. 'Nutmeg liver' appearance of the left hepatic lobe following venous thrombosis. The right hepatic vein is visible (red arrow).