This chapter reviews radiological and pathological images of Budd–Chiari syndrome (BCS), noncirrhotic portal vein thrombosis (PVT), portosinusoidal vascular disease (PSVD), sinusoidal obstruction syndrome (SOS), and peliosis hepatitis. All these diseases have in common an involvement of the hepatic vasculature bed, which consequently causes alterations of the hepatic parenchyma and portal hypertension.

In BCS, severity of liver injury will depend on the extent of involvement of the hepatic veins, the time course over which the obstruction of the hepatic veins develops and the delay in receiving an adequate treatment. Slow development of the obstruction allows the creation of collateral veins, which alleviates sinusoidal congestion as the obstruction progresses. These collaterals are veins that do not follow the normal direction of hepatic vein flow and are easily detected in color doppler ultrasound as illustrated in Figure 60.1. Common radiological features of BCS are shown in Figure 60.2 and include atrophy of segments that are not adequately drained, hypertrophy of the caudate lobe, enlargement of the caudate vein, collateral circulation, ascites, and portal vein thrombosis. As seen in Figure 60.3, hepatic vein venography may show a spider‐web pattern, which is characteristic of this entity. In acute BCS, there is centrilobular and sometimes midlobular sinusoidal congestion, acute hemorrhage, and hepatocyte ischemia or drop‐out. Figure 60.4 demonstrates hemorrhage within the hepatic cords with red blood cells replacing the damaged hepatocytes. In chronic BCS, chronic outflow obstruction may lead to bridging fibrosis between terminal hepatic venules with sparing of the portal tracts and fibrosis that obliterates the terminal hepatic venules, as demonstrated in Figure 60.5.

Noncirrhotic portal vein thrombosis may present as one of two distinct clinical scenarios: acute or chronic PVT. These represent successive stages of the same disease and have similar causes but different clinical presentation and management. Presence of hyperattenuating material in the lumen of the vein, lack of significant portoportal collaterals, and lack of signs of portal hypertension on imaging are characteristic features of acute PVT which can be seen in Figure 60.6. In the chronic phase of PVT, imaging shows the presence of a network of small irregular collateral vessels, the absence of the main portal vein and its main branches and other signs of portal hypertension (Figure 60.7). Portal cholangiopathy refers to compression of the bile ducts by a portal cavernoma. Radiological abnormalities such as stenosis, dilation, angulation or irregularity of the bile ducts are frequent and are displayed in Figure 60.8.

Recently, portal vein recanalization has gained increasing acceptance as a therapeutic option for patients with chronic PVT with severe or refractory complications of portal hypertension given that, as illustrated in Figure 60.9, it may restore the physiological blood flow through the portal vein without the need for placing a transjugular intrahepatic portosystemic shunt (TIPS).

The term PSVD has been recently proposed to describe a broad range of pathological abnormalities that involve the portal venules or sinusoids. These histological entities were previously grouped under the term noncirrhotic portal hypertension. Specific features include obliterative portal venopathy, nodular regenerative hyperplasia, and incomplete septal cirrhosis. Figures 60.10 and 60.11 demonstrate small regenerative nodules, which are composed of cytologically benign hepatocytes. The nodules displace portal structures and are surrounded by areas with atrophic hepatocytes. Nonspecific features of PSVD include sinusoidal dilation, herniation of the portal vessels into the parenchyma, hypervascularized portal tracts, periportal abnormal vessels, and mild perisinusoidal fibrosis, which can be seen in Figure 60.12. When portal hypertension develops in patients with PSVD, imaging may show alterations in the morphology of the liver and signs of portal hypertension, all of which may be indistinguishable from those seen in cirrhosis (Figure 60.13).

Sinusoidal obstruction syndrome (SOS, previously known as hepatic venoocclusive disease) is initiated by damage to liver sinusoidal endothelial cells. Figure 60.14 demonstrates the ultrastructural changes in the sinusoid that occur prior to “clinical” evidence of disease in the experimental model, notably formation of gaps in the sinusoidal endothelial cell barrier that allow penetration of red blood cells through the gaps into the space of Disse. Figure 60.15 demonstrates the ultrastructural features of early SOS in a rat model with denudation of the sinusoidal lining and loss of hepatocyte microvilli during early SOS. The histological features of early SOS shown in Figure 60.16

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