A seroma is a pocket of clear serous fluid (filtered blood plasma). They may sometimes develop in the body after surgery, particularly after breast surgery, abdominal surgery, and reconstructive surgery. They can be diagnosed by physical signs, and with a CT scan. Seromas can be difficult to manage. Serous fluid may leak out naturally, and a persistent leak can cause problems. Fluid can be drained, including by inserting a drain surgically. Seromas can be prevented through careful surgery, and drains can be inserted before they form. Patient posturing and position can reduce risk, as well as breast binding after breast surgery. Etymology Around 16th century CE, the word originated from , meaning "watery" later the meaning changed to "of, secreting, or containing serum". It is directly derived from , meaning "watery fluid, whey". It was joined with a word-forming element from , with -o-, lengthened stem vowel + -ma suffix, especially taken in medical use as "tumor" or "morbid growth". Classification A seroma contains serous fluid. This is composed of blood plasma that has seeped out of ruptured small blood vessels and the inflammatory fluid produced by injured and dying cells. Seromas are different from hematomas, which contain red blood cells, and abscesses, which contain pus and result from an infection. Serous fluid is also different from lymph. Signs and symptoms A seroma can usually be felt as a hard mass under the skin. This may cause erythema (skin redness). They can also cause significant pain. Cause A seroma is usually caused by surgery. Seromas are particularly common after breast surgery (e.g., mastectomy), abdominal surgery, and reconstructive surgery. It can also be seen after neck surgery, thyroid and parathyroid surgery, and hernia repair. The larger the surgical intervention, the more likely that seromas form. Early or improper removal of sutures can sometimes lead to formation of seroma or discharge of serous fluid from operative areas. Seromas can also sometimes be caused by injury, such as when the initial swelling from a blow or fall does not fully subside. The remaining serous fluid causes a seroma that the body usually absorbs gradually over time (often taking many days or weeks), but a knot of calcified tissue sometimes remains. Large seromas take longer to resolve than small ones, and they are more likely to undergo secondary infection. A seroma may persist for several months, or even years as the surrounding tissue hardens.