Liver cancer. Coloured computed tomography (CT) scan through the abdomen of a patient with secondary liver cancer (black). The patient also has a portal vein thrombus (blood clot), which is being complicated by the presence of venous gas. People with cancer are prone to developing blood clots (thrombosis). While the thrombus remains in a vein, it restricts oxygen flow to the venous tissue (ischaemia), causing the production of venous gas. The build-up of gas can cause the thombus to become dislodged and be transported ultimately to the lungs (pulmonary embolism), which can prove fatal.