Blood Blister in my cat's ear?

[Dante_Sonata]

My cat, Smokey, has what looks like a large bubble filled with blood on the inside of his ear flap. He's had it for quite some time -- over a year -- and when I initially noticed it, it was rather small, and there were two. I showed it to the vet at that time, and I believe he said it was just a blood blister; he drained it, and said not to worry about it. I called him back later, when the larger of the two reappeared, and he told me that I could sterilize a safety pin and drain it myself if I felt comfortable doing so, or else I could just leave it be.
Today, I was petting him and took a look at his ears. The main blister, or whatever it is, was back, and about the size of my pinkie nail. I drained it again, like the vet showed me, but now I'm curious.
Has anyone ever had an issue like this? Know of a good way to get them to go away for good? It's just the one blister that keeps reappearing -- the smaller ones that the vet drained initially haven't returned. I've gone extended periods without draining it, just to see if maybe it will go away on it's own, and all it does it get bigger. It never seems to really hurt or bother him, I can poke and prod at it with my finger and he just sits there. The drainage is sort of a mixture of old blood and pus, and it doesn't bleed fresh blood once I've gotten all of the pus squeezed out of it.  

[Cowgirl-with-heart]

its probably a hematoma,and he keeps breaking it open,it doesnt make sense that a blood blister would continually re-appear,unless if he has a weak vessel in his ear