Vascular liver diseases (VLDs) – summarised in Table 11.1 – are a heterogeneous group of diseases affecting one or more of the liver vessels, either at micro‐ or macroscopic level. Many of them are rare or very rare and it is important to note that several VLDs occur in association with, or because of systemic diseases. The latter should therefore be carefully excluded with a VLD diagnosis. The approach and management vary largely according to the type of VLD (see below), ranging from anticoagulation for thrombotic disorders, to interventional radiology techniques (e.g. for large arteriovenous fistulae) and to liver transplantation in selected cases.

Among clinically relevant VLDs, thrombotic diseases of the portal vein and of the hepatic veins constitute the largest proportion. In all patients presenting with signs of portal hypertension, thrombotic diseases should be ruled out since they are the second commonest cause of this syndrome after cirrhosis.

Ultrasound techniques are very useful in identifying and characterising many VLDs and their associations. Ultrasound is the first modality of choice when there is a clinical suspicion of VLD.

This chapter aims to summarise the evidence supporting the use of ultrasound and elastography techniques for the main VLDs.

Portal Vein Thrombosis and Extrahepatic Portal Vein Obstruction

Thrombosis of the portal venous system, or portal vein thrombosis (PVT), is defined by the presence of a clot in the lumen of the vessel at any level (extrahepatic trunk, intrahepatic branches, splenic vein, mesenteric veins), or by the substitution of the vessel with porto‐portal collaterals (cavernous transformation) [1]. Cirrhosis and prothrombotic diseases (either congenital or acquired) are risk factors for the onset of PVT. In cirrhosis, cross‐sectional studies showed prevalences of up to 20% with an incidence of 5–7% per year, while in the general population the risk of PVT is deemed to be <1% in a lifetime [2]. PVT occurring in subjects without cirrhosis is more correctly termed extrahepatic portal vein obstruction (EHPVO) and should prompt a complete work‐up of thrombophilia, including ruling out myeloproliferative neoplasms (JAK2, calreticulin, MPL gene mutations and bone marrow biopsy in selected cases); paroxysmal nocturnal haemoglobinuria (flow cytometry for CD55 and CD59), Behcet’s disease; antiphospholipid syndrome; mutations of Factor II, Factor V, ATIII, Protein C and Protein S, human immunodeficiency virus (HIV) infection, coeliac disease autoimmune and inflammatory systemic diseases [2].

Presentation varies from totally asymptomatic cases identified on imaging done for other causes to abdominal pain, to complications of portal hypertension or intestinal ischaemia. These depend on the severity of occlusion, site of occlusion, duration, extension, and comorbidities. These factors are taken into account in a recent anatomical‐functional classification [3].

On suspicion of PVT, ultrasound should be used as a first‐line technique, since its sensitivity and specificity for thrombosis exceeds 90% [4]. An endoluminal clot or absence of flow or cavernous transformation of at least one of the vessels of the portal system defines PVT. The clot can have an echogenic or hypoechogenic component, and can completely or partially (Figure 11.1) occupy the lumen. The clot is better visualised on greyscale ultrasound but colour and spectral Doppler can help characterise the degree of occlusion (complete/partial with residual flow) [4]. By using the latter techniques, attention should be paid to using the lowest possible scale to avoid false positives owing to slow flow (e.g. in decompensated cirrhosis or in patients on non‐selective beta‐blockers). The cavernous transformation of the portal vein is identified by porto‐portal tortuous collateral vessel substituting (surrounding or within) the thrombosed vessel (Figure 11.2). It can occur at any level of the portal venous system (intra‐ or extrahepatic).

In addition, ultrasound not only detects the presence of PVT, but also provides information on factors that may predict its recanalisation with anticoagulation therapy, as well as clinical outcomes [4]. These can be summarised as follows:

• Absence/presence of cirrhosis: cirrhosis represents per se a risk factor for PVT. An active search for signs of cirrhosis (e.g. nodular liver surface; heterogeneous parenchyma; caudate and left lobe hypertrophy, splenomegaly, and recanalised paraumbilical vein) should be performed [5]. Since long‐lasting thrombosis can alter the liver shape, mimicking cirrhosis, the use of elastography can be very helpful in diagnosing cirrhosis in this setting, since liver stiffness is markedly increased only in patients with cirrhosis and not in patients with EHPVO [6]. Spleen stiffness is elevated in both conditions, and is not helpful in the differential diagnosis.
  
• Duration of thrombosis: a well‐recognisable vessel with hypoechoic material in the lumen can suggest recent thrombosis in patients who have developed symptoms. On the other hand, the presence of calcifications in the thrombus or in the walls of the involved vessels is considered a sign of long‐lasting thrombosis. Other signs, such as large splenomegaly or degree of porto‐systemic and porto‐portal collateralisation, cannot be considered specific of long‐lasting thrombosis owing to the many confounders that can be encountered in patients with PVT (e.g. myeloproliferative diseases leading per se to splenomegaly; cirrhosis leading to porto‐systemic collaterals previous to PVT, etc.), and due to the fact that cavernous transformation has a very early onset (within days/weeks from the acute thrombotic episode) (Figure 11.3).
  
• Presence of vessels that can allow interventions: the presence and size of a remnant portal vein, and/or the dominant vessel within the cavernoma, and the patency of the splenic vein and superior mesenteric vein are key pieces of information to select patients in whom a transjugular intrahepatic porto‐systemic shunt (TIPS) or recanalisation procedures can be attempted. For a detailed mapping of the extension of the thrombosis and of the anatomy of the existing collaterals, cross‐sectional contrast‐enhanced imaging methods (contrast‐enhanced computed tomography, CECT, or contrast‐enhanced magnetic resonance, CEMR) should be preferred. These methods can also provide information on the presence of extrahepatic malignancies or inflammatory foci.
  
• Nature of thrombosis (benign; neoplastic vascular invasion): PVT in patients with hepatocellular carcinoma or cholangiocellular carcinoma and patients in whom both a liver tumour and PVT are detected simultaneously represents a diagnostic challenge, since both bland thrombosis and neoplastic vascular invasion should be considered, and macroscopic vascular invasion in patients with hepatocellular carcinoma (HCC) identifies an advanced stage of the disease, currently not suitable for curative treatment options [7]. On ultrasound, the following signs suggest neoplastic vascular invasion: expansive aspect (>2 cm) of the vessel, interruption of the walls, and presence of signs of arterial perfusion in the thrombus. The latter can sometimes be identified by colour Doppler and pulsed Doppler (arterial flow with high resistance index). The use of contrast‐enhanced ultrasound (CEUS) improved the accuracy of ultrasound to diagnose neoplastic invasion of the portal vein, demonstrating wash‐in in the arterial phase and wash‐out in the late phase (usually quicker than the primary tumour) (Figure 11.4) [8].
  
• Presence of portal biliopathy: this is characterised by gallbladder and biliary duct abnormalities, leading to cholestasis due to the cavernous transformation [9]. While magnetic resonance cholangiopancreatography (MRCP) is the reference standard method to diagnose and stage this complication, the dilatation of biliary ducts can often be seen on ultrasound and should be reported.

Intrahepatic Non‐cirrhotic Portal Hypertension

Porto‐sinusoidal Vascular Disorder/Idiopathic Portal Hypertension

The term ‘porto‐sinusoidal vascular disorder’ (PSVD) has been proposed recently [10] to designate a group of conditions that present histological alterations that involve the portal venules and/or sinusoids without the presence of cirrhosis. It may or may not be associated with portal hypertension. This term groups entities such as idiopathic portal hypertension, idiopathic portal fibrosis, obliterative portal venopathy, hepatoportal sclerosis, incomplete septal cirrhosis, and nodular regenerative hyperplasia (NRH). Specific causes of VLDs are not included in the term.

The pathogenesis of PSVD is unknown, but in around 50% of patients it is associated with haematological diseases, immunological disorders, drug exposure, abdominal infections, or congenital defects.

Doppler ultrasound is the first step in the imaging evaluation of PSVD, although there are no specific sonographic features that allow the diagnosis to be established. The most frequent findings are those secondary to portal hypertension: dilated spleno‐portal axis, splenomegaly, and porto‐systemic collaterals. Although the morphology of the liver can be normal, it is frequent to find architectural changes corresponding to a hypertrophy of the caudate lobe and segment IV, with atrophy of the right lobe. In advanced stages, the liver surface could become irregular and it can be indistinguishable from liver cirrhosis (Figure 11.5

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