I agree with the hematoma diagnosis. Usually they are caused by excessive shaking of the head. You should check the ear for mites or a foreign body causing irritation.
As for the hematoma itself, you should lance the ear and then express as much blood as possible. Swab the ear well with rubbing alcohol first so it is relatively sterile. Put cotton balls into the ear canal so blood does not drain into it. It would actually be best to lance the "fur side" of the ear so you can lance it at the bottom of the "blister" nearest the base of the ear and not have to worry about blood draining into the ear canal, but if the tissue is not distended as it is on the inner surface, this might be more painful.
Prior to doing this, look at the other ear so you can see where the main veins run so you can hopefully avoid cutting into them.
I would then irrigate the wound with either a weak Betadine and water solution (it should look like tea), or hydrogen peroxide in order to rinse as much coagulated blood out as possible. Betadine is the veterinary version of povidine iodine, which you may have in your own first aid kit.
If the ear is not sutured, it may crumple and shrivel which will disfigure the ear but will not cause any health issues. When this happens, it is commonly called a "cauliflower ear".
DitchDoc":10azeof6 said:
Your bunny probably won't appreciate it but if you can get your hands on some viscous or topical lidocaine, it would help with the pain if you choose that route.
I once lanced a dog's ear for a friend of mine, since taking the dog to the vet was not an option. He didn't seem to even feel it when I sliced into the ear.
I also know someone that marks their bucks by cutting the top inch or so off of the ear. I know it sounds awful, but they are cattle ranchers and in addition to branding their cows they also slice the ears in a specific way as part of their "brand", so it made perfect sense to them to do the same with their rabbits. I have seen them do it, and the rabbits don't react. :shock:
However, if you are worried about the pain, and can't get any lidocaine, you could apply oral antiseptic gel (Orajel) which contains Benzocaine, an anesthetic in the same family. Icing the ear prior to making your incision will also help.
Good luck! :clover: