Dear Patient, Welcome, and thanks for sharing your concern I went through your query, and I feel, since it is of recent onset, it could not be a tumor growth, with history of injury, this could well be either blood, or it could be pus following the infection in collected blood, note if you have fever or there is raised temperature at the swelling, if so than the chances of its being infective will be more, also see your doctor and ask him to aspirate it and see the content, weather it is blood or pus. I hope my advice would have been useful, in decision making regarding your treatment, still if you have any clarifications or doubts feel free to contact back. Thanks