Xarelto Versus no Treatment for the Prevention of Recurrent Thrombosis in Patients With Chronic Portal Vein Thrombosis.

Inclusion Criteria: * adult patients aged 18 to 90 years old * Patients either with : * Portal cavernoma radiologically confirmed, treated or not by anticoagulant * previous history of acute portal thrombosis for more than 6 months confirmed by angio-TDM or angio-MRI, repermeabilized or not * prophylaxis of gastro-intestinal bleeding due to portal hypertension, as recommended for cirrhosis patients. Upper gastro-intestinal endoscopy for less than 12 months * clinical examination * for women of childbearing age, contraception, either mecanichal or intra-uterin device, or oral progestative alone. No oral oestroprogestative contraception is allowed. * written informed consent * covered by a social security scheme or French "CMU" Exclusion Criteria: * At least one High risk factors of thrombosis recurrence after review by the committee composed of an hepatologist and an hematologist specialist of hemostasis * Cirrhosis clinically or histologically confirmed or Budd-Chiari syndrome * Any disease leading to significant coagulopathy and clinically significant bleeding risk (platelets \<50 000, or PT \<30% without VKA, or Factor V \<30% or Fibrinogen \<0,8). * Personal or familial (1rst degree) history of spontanaeous deep vein thrombosis requiring anticoagulant treatment * pregnant or breast-feeding women * History of mesenteric veinous ischemia leading to intestinal resection * patient infected by HIV and treated by anti-protease * Formal indication to anticoagulant treatment for any reason * No possible follow-up * severe renal injury (creatinin clearance \<30 ml/min) * Patients receiving a systemic treatment by azoled antifongic agent (such as ketoconazole, itraconazole, voriconazole or posaconazole), or a protease inhibitor. These are strong CYP3A4 and P-gp inhibitors. * Patients receiving a systemic treatment by rifampicyn or any other strong CYP3A4 inducting/stimulator (phenytoïne, carbamazepine, phenobarbital or millepertuis/Hypericum perforatum) * Hypersensitvity to rivaroxaban or excipients * active bleeding, or any condition at risk for significant major bleeding * Any other concomitant anticoagulant treatment, such as non-fractionnaed heparin, low-molecular weight heparin (enoxaparin, dalteparine, etc…), heparin derivatives (fondaparinux, etc), oral anticoagulant (warfarine, dabigatran etexilate, apixaban, etc) except in case of switch to Xarelto® or, in case of non-fractionnaed heparin administered to maintain central veinous or arterial catheterism permeability * Concomitant treatment by clopidogrel / Plavix® for acute coronary syndrome * hepatic transplantation * Intra-hepatic shunt