Phlebothrombosis occurs when a blood clot ( thrombosis ) in a vein ( phlebo ) forms independently from the presence of inflammation of the vein ( phlebitis ). Thrombophlebitis is phlebitis (vein inflammation) related to a thrombus (blood clot). These conditions are usually of the superficial veins and are generally mild and uncomplicated as opposed to deep vein thromboses, which can be life-threatening. [1] [ better source needed ]