I had one and it went away. I got it, I think, from riding too hard on my handlebars whilst going over bumpy roads. It'd come back periodically but I haven't seen it for a long time. Someone I know referred to it as a "bible bump" because the way to cure 'em in the old days was to smash a bible down on it so it'd burst.

I was concerned when I had it but that was a long time ago. I notice my range of motion in that wrist is slightly less now but that might be because I started favoring it.