I had my gall bladder removed 2wks ago. I had a lot of swelling on the left side of my abdomen. I went in yesterday & they did a CT scan w/ contrast. They said I had a seroma.It is common after surgeries. It is actually serum from blood cells that were cut. It pools & causes some pain. They took a needle & aspirated it & took 150 ml from me–over a cup. The rest will eventually be absorbed. If too much is there it can cause a hardening.