About 4 years ago my horse came in from T/O with a large hard lump on his nasal bone. There was no trauma associated with it (loss of hair, scratch etc) and he didnt react to applied pressure or poking and prodding. I called the vet because it was on his nose and it was large so I was concerned about breathing.

After X-rays and input from New Bolton all parties agreed it was a bone bruise. When I asked if it would go away, they couldn’t give me a solid answer. Well, 4 months later it had disappeared.

Now, one seems to occur about once a year. Never in the same place, always the same symptoms (although, they have never been as large as the first initial one) and they always disappear. Obviously, the bigger they are the longer they take but they always go away.
Im not worried about it more curious as to what is it? Causes?
I will be the first to admit that he can be reckless with his head and seems to not be aware that there is a large object attached up there, but I would think if it was caused by that there would be some sort of visual area or impact, even missing a couple hairs or something. But there is never anything...
Any Ideas?