Irregularly-Shaped Lump on Cat Belly

[Sai_Rhy]

Hello. My cat has a lump growing on his belly. He had a surgery to remove bladder stones as he had urinary blockage about 2-3 months ago. After surgery, he had like a little dot of flesh sticking out when the incision fully healed after 14 days. The vet said it was nothing to worry about. After some time, the flesh went back inside and only a tiny dot is now left.
However, lumps are now growing around the little dot. It has quite an irregular shape. My cat's behaviour is perfectly normal and he doesn't seem to be bothered by it. Of course, I brought him to the vet 5 days ago, just to be safe. He performed an x-ray on my cat and told me he is having something called fibrose tissue growing under his belly, and suggested to remove it by surgery after 20 days, but that it should be removed earlier if I notice it is growing rapidly.
I am attaching a photo taken today. Please I would like an advice on the matter. Have anyone experienced similar problems with their cats? I have read on several stuffs online already, mentioning problems like abscesses, lipomas, fibrosarcomas, mast-cell tumors, etc. I am really worried for him and I would like to take the right steps to make sure he is okay. Is the surgery necessary or can this lump go away on its own? I am also worried about post-surgery issues and possible recurrences.

Ps: I could not get a clear photo of the lumps as he hates being in this position in general.

 

[di and bob]

These are usually caused by trauma to the skin and underlying tissue, so are not uncommon after surgery. They are usually slow-growing and are not removed surgically until they become bothersome. They do often come back after surgery. If it worries you quite a bit, have it biopsied the next time you are in, and if benign, have it removed when it gets annoying to the cat. It may be so slow-growing it never reaches that stage.

 

[Sai_Rhy]

I see. The vet did tell me that it may be related to a trauma to the skin as you mentioned. But for some reason there are very few articles that I could find online on this particular problem.
Is there anyway to distinguish visually between this kind of trauma (fibrose tissue) and other problems which may cause lumps (such as abscess, lipoma, fibrosarcoma, etc.).
I will bring him to the vet again to do a biopsy just to be sure. Will a fine needle aspiration help to determine the underlying problem?
Thank you very much for your comment. It certainly gave me a better insight on what I should do.

 

[di and bob]

Well, the timing and the location narrows it down. If it were me I would monitor it for a while and see how it does. If it is slow growing and doesn't bother him, you have a while to think of what to do. I definitely rely on what my vet tells me, he's seen a lot. But things can be different too, he told me my very critically sick cat with leukemia only had days to a week left and he's still with me 2 years later, fat and sassy!