 Venous thrombosis may also occur in more unusual places : in the veins of the brain , liver ( portal vein thrombosis and hepatic vein thrombosis ) , mesenteric vein , kidney ( renal vein thrombosis ) and the veins of the arms . Whether thrombophilia also increases the risk of arterial thrombosis ( which is the underlying cause of heart attacks and strokes ) is less well established . 
