I am sorry to hear you are worried about your cat.
My name is***** am a veterinarian, and will do my best to help.
Something similar happened to my own dog years ago: Had an FHO for a fracture, and about 5 years later the area got swollen, warm, painful.
I was sure it was an infection; something smoldering from the old surgery ( which did get infected post op). I got a sample for a culture, and just to be complete, sent it out for histopathology as well.
So, I would get not just a needle biopsy, but a piece of this for both culture and histopath. You need to find out what it is as soon as possible, and then you will know the best way to treat it. I hope for your cat that is it an infection, and a culture can tell you the best antibiotic or therapy, but from your description, and my own experience, you need to be sure it is not a neoplasm.
I am not seeing responses from you. Sometimes there are problems with live chat, and we don't see what the other is writing.
Sorry - replying soon - just thinking!
Take your time!
I am just glad to see you are seeing what I write.
I guess chances of an accurate diagnosis DURING an amputation op (i.e. Visual appearance) are not very good...
If this were my own cat, I would sedate him, put in some local anesthetic, and get a surgical biopsy.
I would not do amputation before getting a diagnosis. If it is in the pelvis, it won't be removed with amputation.
I would get a diagnosis first, if it were my own cat.
Would any other imaging be useful do you think - u/sound, CT - or biopsy / culture best way to go?
Ultrasound and CT and MRI would all be interesting, but the only way to get a diagnosis would be to get some tissue.
OK, thanks. And not just an aspirate, but actual tissue / bone?
Imaging would help if amputation is considered, so you know how far to go. Taking part of the pelvis, however, could be a very invasive surgery.
Yes, I would get a solid chunk of this mass. It would not have to be a huge piece.
OK, thanks. I think out vets are thinking it must be 'degenerative' given prev surgery, but it looks way beyond that now.
Was the blood that was aspirated sent for culture or cytology? Was it just peripheral blood?
It does not sound like degenerative disease to me. It is sadly reminiscent of my dear "Pudgy".
So I hope my experience is not what is going on with your cat.
Was blood out of the actual swelling, but none sent for any kind of lab work.
Thanks for the advice - I think we'll ask for culture and histopath as you suggest, then take it form there.
You are welcome.
I would be interested to hear what you learn.
I will be following up to see how he is dong and what you find out.
Is there anything else I can answer now?
No, that's great, thanks.
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I'll click the smiley face and sign off now.
We had our cat put to sleep yesterday I am more than happy to let your expert know about this, but I'm not paying for the privilege. Any suggestions?