Hematoma. A collection of blood outside a blood vessel caused by a leak or injury.
Hematomas may occur after surgery or an injury and may feel like a lump.
Like a bruise, a hematoma is a mark on your skin because blood is trapped under the surface. A hematoma usually refers to the mark created when blood builds up in a surgical wound where tissue has been removed. Hematomas can be caused by breast cancer surgery: lymph node removal