I have one, in my foot.
At least, that's what I think it is based on Yahoo doctor and stuff.
Kinda all red and bloody lookin.

(Backstory: got booted in the shin about two weeks ago. Shin swelled up. Has now gone down but there are bruises and bumps all over it and my ankle's aching now... and just below the ankle is this vast spread of red, just below the skin. Hence me looking it up.)

Um, does anyone know much about such things? Will it just go away or do I need to see someone? It hurts, but not a great deal - I can still walk. Well, hobble, kinda.

Ho hum...