Help Find What's Wrong With Rengar

Hello!

My name is Forrest, and this is my buddy, Rengar. 
Rengar is an adopted cat my girlfriend and I picked up about 2 months ago. He's a year old, and he's quite the special case. He's polydactly, so he has an extra toe on each of his front paws. Unfortunately, that's not all that's special about him. Recently, he's taken ill. We have spent over $800 on vet bills so far, and the best answer we've gotten is "I don't know". We had Xrays done, and they've caused more questions than answers.

As you can see in the circled spots, there are some abnormalities that have left us, and the vets we've visited quite stumped. We're not sure what they are, and our only options going forward is an ultra sound. We have 2 other cats, both rescues as well, and are no strangers to expensive vet bills, but Rengar's are adding up quick. We are turning to compassionate people for help, we simply cannot do this on our own right now, and we want nothing less than a perfect life for our little buddy.
Rengar is quite the fierce hunter, much to Banin's enjoyment, and we want to keep him that way. Please, if you can, any donation, or even passing this along, will help. 

Let's figure out what's wrong with Rengar, and let's get it fixed. Thank you.