Lump under left rib cage (Possible tumor or just stomach?)

[IsaBun03]

Hello, new member here (although I have used the forum for research before)
My rabbit Tanya, around 4 years old, has a quite large (perhaps a golf ball) sized, hard lump on the left side of her body, right underneath her rib cage. I noticed it at least 4 months ago, and it seems to get softer and harder at times, but it stays mostly the same size.
I feed her a bit of greens (almost) every morning (lettuce, dandelion, spinach, kale, collard, mustard, occaisionally fruits), along with around 2 tablespoons of oxbow pellets and always orchard grass hay. She eats normally, drinks a loooot (she loves pedialyte, also).

I had assumed that the lump was her stomach, but the constant hardness makes me think otherwise.
Context: Just around 30 minutes ago, I checked her stomach and it felt much much bigger, so I gave her 5mL of baby gas drops and massaged her stomach, and now it seems back to normal. This morning and last night, I did give her some chunks of papaya, as well as blackberries. Not sure if that is the cause of this, though. I am concerned it could be a Thymoma or some kind of tumor.

Please, thoughts?

 

[JBun]

You wouldn't feel a thymoma. It would be further up in the chest near the heart. And your rabbit would likely be showing other signs of having a thymoma (labored breathing, unusual fatigue, weight loss, protruding third eyelids, consistently trying to keep the head elevated even when resting, sebaceous adenitis, etc)

The stomach is under the left side of the ribs, and full of food and fluids you might be able to feel it. I only noticed feeling it when I had a rabbit with bloat, and it felt like a hard inflated ballon, but it is possible to feel it when it's not bloat but very full of food and fluids, though shouldn't be very distended and the rabbit shouldn't be acting unusual or sick. If your rabbit just ate and drank a bunch when you feel it, but is still acting normal, it's not something I see as abnormal or would worry about.

But if the lump does seem abnormal, gets bigger, your rabbit is showing signs of bloat/gas or feeling unwell, and/or you have any concerns that your rabbit is unwell or there's a problem, then it's best to contact a knowledgeable rabbit vet right away, to have your bun checked out. Particularly in a case of true bloat, which is an immediate emergency.

https://wabbitwiki.com/wiki/Veterinary_emergencies
https://wabbitwiki.com/wiki/Choosing_a_rabbit_veterinarian
https://rabbit.org/veterinarians/
If you notice your bun feeling unwell after eating certain foods, I'd recommend not feeding those foods anymore. Also, limit high carb/sugary foods. And always introduce new foods into the diet, one at a time in a small amount, and only increase gradually over several days if there are no signs of digestive upset.

https://rabbitsindoors.weebly.com/feeding.html
Medirabbit: feeding rabbits