**2. Portal vein thrombosis**

The haemostasis disruption may lead to macro-vascular thromboses involving the complex circulation around the liver, i.e. the portal venous system (PVS) that includes the intra-hepatic portal vein branches, the splenic and superior mesenteric veins. Portal vein thrombosis (PVT) commonly occurs in patients with hepatic cirrhosis and/or carcinoma, while splenic vein thrombosis may also be found as an extension of a PVT or develop as a complication of splenectomy [4, 5]. PVT may also develop in the absence of primary liver disease [6] and has recently been described in patients with COVID-19 [7, 8] and in patients suffering vaccine-induced immune thrombocytopenic thrombosis (VITT) following COVID-19 vaccination [9].

In patients with cirrhosis the frequency of PVT increases with disease severity [10] from about 3%–25% [11]. In post-splenectomy patients with cirrhosis the frequency may reach 36% in the absence of anticoagulation and rates as high as 70%–5% have been found in the presence of malignancy (hepatoma, lymphomas, solid tumours, myeloproliferative neoplasms). Although at first PVT may be almost symptomless and many spontaneously disappear, persistence and recurrence result in significant or complete obstruction of one or more vessels of the PVS and portal hypertension with increasing morbidity. Formation of collateral circulations and varices are prone to rupture with often major blood loss. PVT can present either acutely with abdominal pain, diarrhoea and ileus—occasionally as an acute abdomen or chronically often with signs of portal hypertension.

Persistent/recurrent PVS thrombosis (PVST) may eventually be fatal, hence there is frequently a need for effective antithrombotic management. Especially if acute non-occlusive PVST or a thrombotic risk factor is present, e.g. sepsis, cancer, antiphospholipid antibody or an acquired or hereditary thrombotic risk (factor V Leiden, prothrombin mutation G20210A, protein C and/or S deficiency, etc.) then anticoagulation should be considered [12, 13]. The aims of anticoagulation are thrombus recanalisation, reduction of portal hypertension to lower the bleeding risk and prevention of PVST recurrence. The use of anticoagulants has been reviewed and several meta-analyses of the results are available [5, 14]. Despite the heterogeneity of the included studies, there appears to be a growing consensus that use of anticoagulants for the treatment of PVT increases the rate of recanalisation compared with non-anticoagulated patients, but there is too little evidence concerning their benefit to risk balance with emphasis on bleeding complications.
