A<unk>  is usually caused by surgery.<unk> s 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<unk> s form. Early or improper removal of sutures can sometimes lead to formation of<unk>  or discharge of serous fluid from operative areas.<unk> s 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<unk>  that the body usually absorbs gradually over time (often taking many days or weeks), but a knot of calcified tissue sometimes remains. Large<unk> s take longer to resolve than small ones, and they are more likely to undergo secondary infection. A<unk>  may persist for several months, or even years as the surrounding tissue hardens.<unk>  is the most common surgical complication after breast surgery. It is due to the presence of rich lymphatic system in the breast, low fibrinogen levels in lymph fluid and potential space creation in the breast after surgery, which contributes to<unk>  formation.<unk>  is more common in older and obese people.
Seroma
Stoma 
Encephalitis
Brain abscess
Meninges
Cerebritis
Hematoma
Meningitis