Cat ear problem.

Question
My cat has had ear mites, but were treated. now he has them again, but this time his right ear has enlarged to the point were you can't see into his ear at all. i was wondering if you could tell what could have caused his ear to swell up.

Answer

aural hematoma   Your cat probably has a aural hematoma in his ear. What happens is that when their ears itch bad enough they will scratch them really hard and thus rupture a blood vessel right under the surface of the skin. When that happens, the blood has no where to go from the broken vein so it fills up the ear under the skin, pushing the skin out until it balloons up. Basically it's like a giant blood blister between the layers of skin and cartilage.  

Since the ear canal is rather small it fills it up with the tissue, effectively blocking your view into the ear.

This is a condition that needs to be treated by the vet. The vet will give the cat a sedative then drain the blood from the ear, suture the skin back down with some sort of padding and then send the cat home for a week or so. Then you will bring him back to have the sutures removed. At that time the vet will assess the ear flap and hopefully it will have sealed itself back up.

So call your vet Monday morning and take him in to get this taken care of.

Here is an image of a cat's ear with a aural hematoma.
http://www.askavetquestion.com/earhematoma.php

and an article on how they are treated:

http://www.petplace.com/article-printer-friendly.aspx?id=404