What causes fluids to build up in sites that have had surgery such as lumpectomy?

Natural course: When the body is injured or operated on with surgery, fluid is sent to the area as part of the healing process. In the breast, this is called a seroma. The seroma fills the lumpectomy space. These days we close the space down to decrease the rate of seroma formation. A drain can be placed at the time of surgery to keep the fluid from building up or the fluid can be drained with a needle.