Raised area on axolotl's head-Injury? Illness? Ideas welcome!

Hello newt and salamander community!

I am writing in hopes that some of you may be able to provide some guidance on my axolotl's condition. My axolotl, Merlin, developed a raised area/bump on his head over the course of a few days. I have been really concerned about this, and I took him to two vets already to get it checked out, but neither vet could come to a formal diagnosis without extensive and very expensive tests (>$600!!!). One vet suggested that it was due to a physical injury which I mentioned to her. Merlin rammed his head into the food dispenser with which I use to feed him. It's basically a turkey baster that I use to feed Merlin pellets which he doesn't catch initially.

During the first few days when I noticed the raised area on his head, he also wasn't eating (which is very odd for him), and he became sluggish, but it was really hot where I live, and I think the sluggishness was due to heat stress more than anything. I put Merlin through "cold therapy," whereby I kept him in ice water for five days. I cleaned the water out daily. I eventually moved him into his 20 gallon tank and he is back to normal. He's eating normally again and swimming around looking healthy as ever...except, he still has that bump on his head! Have any of you seen this before on your axolotls? Do you think it's due to physical injury, and if so, how can I treat this? Does anyone think this could be due to illness instead (I initially thought he was sick because of the lack of enthusiasm to eat and the sluggishness, but those symptoms are gone now)? I took some pictures and included them here.

To provide some history, below is a quick description of Merlin's current living conditions:
He is kept in a filtered, 20 gallon tank, which I only fill halfway with water. It includes a gentle, waterfall rock formation, which has a built-in filter. He has no tankmates at all. The only plant in the tank is an artificial, silk plant, which he really loves and spends time near. The plant was a recent addition, and I will be adding more to make his tank more home-y. The water is kept at a solid 69-70 degrees F. I use the Tetra water dechlorinator to condition the water. The vets tested the water for nitrates, pH, etc. and they saw no cause for concern. I clean the entire tank (the rock formation, the walls of the tank, every inch of it, and do a full water change) every 7 days. I'm a germa-phobe so I try to keep Merlin under the best and cleanest conditions possible. I only feed Merlin sinking pellets (~45% protein, 10% fat max). I decided this diet would be best so that he doesn't get exposed to foods with high levels of fat or foods that could potentially carry parasites. He's never eaten any other type of food, but loves his pellets, so it doesn't seem to bother him!

Merlin is about 2 years old. I've had him for about a year and 10 months. He's never had any problems in the past and looks healthy in general. He is a wild-type axolotl.

I apologize for the long message; I just want to make sure you are all aware of the details so that we can resolve this issue as soon as possible! Thank you in advance! Merlin and I greatly appreciate it.

It looks very much like an abcess - he needs to see a vet to have it drained and given a course of antibiotics.

Hi auntiejude,

Thanks for your reply and your thoughts. That's actually what I was thinking; it looks a lot like a fluid build-up of some sort, possibly a response to the physical injury. I'm calling the vet I took him to tomorrow to discuss bringing him in for draining. I hope this works out! Thanks again for your input.

P.S. Your little axolotl is adorable