What is the definition of a cyst in dermatology?

In dermatology, a cyst is defined as a closed sac-like structure that can be filled with fluid, semi-solid material, or a gas. The correct answer describes a deep infection that forms due to a significant accumulation of white blood cells, which is often a response to inflammation or infection within the tissue. This can occur when the body is trying to isolate pathogens or debris, leading to the formation of a cyst.

Cysts can develop due to various factors, including infections, blocked sebaceous glands, or other engorgements of tissue, which may result in solid or liquid content. The appearance of white blood cells in a cyst indicates that the body is attempting to fight off an underlying infection.

In contrast, the other choices reflect different dermatological conditions. For instance, a superficial infection caused by bacteria describes an active infection on the skin surface rather than encapsulated fluid. A raised bump filled with sebum and bacteria would refer more specifically to conditions like acne, where the follicle is involved but does not encompass the notion of a cyst. An inflamed area on the surface of the skin could relate to various inflammatory skin conditions, such as dermatitis, not specifically identifying the encapsulated nature of a cyst.