F5 and hyperhomocysteinemia: The other known and reported reasons for such an occurrence are otolaryngological infections leading to Lemierre syndrome, skin and soft tissue infections around the neck, intravenous drug abuse (direct injection into the IJV), recent head/neck surgery, hypercoagulable states such as protein C or S deficiency, factor V Leiden, antithrombin III deficiency, polycythemia, and hyperhomocysteinemia.