What is the definition of a hematoma?

A hematoma is specifically defined as a localized collection of blood outside of blood vessels, usually due to the rupture of blood vessels. This condition typically occurs as a result of trauma or injury, leading to blood pooling in the surrounding tissues. The appearance of a hematoma can manifest as a bruise, where the trapped blood leads to discoloration of the skin, often transitioning through various colors as the body reabsorbs the blood.

The other options, while related to fluid accumulation or swelling, do not accurately represent the characteristics of a hematoma. For instance, a fluid collection in tissues can refer to conditions like edema or seromas, which involve the accumulation of clear fluid rather than blood. Swelling due to infection typically involves inflammation and possibly pus formation, signifying an immune response. Lastly, a fluid-filled cyst refers to a sac that contains liquid or semisolid material, which is entirely different in nature from a hematoma. Thus, the definition that best encapsulates the nature of a hematoma is that it is a bruise with blood trapped under the skin.