The term splanchnic vein thrombosis encompasses Budd-Chiari syndrome (BCS), extrahepatic portal vein obstruction (EHPVO), and mesenteric vein thrombosis.
Risk factors can be local or systemic. A local precipitating factor is rare in BCS, while it is common in patients with portal vein thrombosis. Chronic myeloproliferative neoplasms (MPN) are the leading systemic cause of splanchnic vein thrombosis, and are diagnosed in half BCS patients and one-third of EHPVO patients; the molecular marker JAK2 V617F is detectable in a large majority of patients with overt MPN and up to 40% of patients without overt MPN. Inherited thrombophilia is present in at least one-third of patients, and the factor V Leiden or the prothrombin G20210A mutations are the most common mutations found in BCS or EHPVO patients, respectively. Multiple factors are present in approximately one-third of patients with BCS and two- thirds of patients with portal vein thrombosis.
In a few patient series from the Southern Mediterranean area the high prevalence of MPN and thrombophilia as underlying cause of BCS is confirmed, although the data should be considered preliminary. Peculiar risk factors present in the area are Behcet’s disease and hydatidosis; moreover, the presence of membraneous webs, typically found in Asian patients, can be found in a significant portion of cases.