Hi again,
You have described to me a 9 yr old indoor cat with a pea sized lump on her tail. there are a number of different things that I would be considering if she were on her way in to see me.
I would wonder if this lump were:
1. An abscess - this type of infection is usually caused by a puncture wound such as from a bite from another cat. This seems unlikely in your cat's case.
2. A benign growth - cats do get sebaceous cysts which are harmless, as well as lipomas and other benign tumours of the skin.
3. A malignant growth - cats do also get melanomas and other malignant growths which can show up as bumps on the skin.
When I am presented with a cat with a bump, I do a very careful full physical exam to see if there are any other abnormalities like other bumps or enlarged lymph nodes.
Then, I examine the bump closely.
The first thing that I want to mention is that I tend to be quicker to move to more aggressive measures in a mature cat that is indoors, as infection (abscess) is less likely.
Generally, if any cat comes in to see me and has a lump, and it does not seem to be an abscess (pus inside it), I would recommend testing it to see if it is malignant or benign. There are 3 ways to do this, and they all have their pros and cons. Let me explain:
Fine needle aspirate (FNA) – this is easily done by inserting a small needle into the lump and aspirating (sucking out) some cells to be examined on a slide. This slide may be examined in-hospital by the vet, or sent out to a pathologist (a specialist in this area). The advantages of a FNA are that it is fast, minimally invasive, easy and the least expensive option . The disadvantage is that it is the least effective at making a diagnosis. The reason for this is that lumps are not necessarily homogenous (the same throughout). Imagine, if you will, that I have made an apple pie. I cover it with a tea towel and give you a straw. I ask you to figure out what it under the tea towel. You insert the straw and suck up a sample which you put on a plate to examine. If you got crust, apples and sauce, you will probably correctly diagnose apple pie. If, however, you got crust and sauce, but did not happen to hit any apple, you might think it was a peach pie! The same applies to lumps – there can be different areas within them, and it is random luck whether you will hit a diagnostic area.
2. Biopsy – with this method of testing the lump, a wedge or piece of the mass is taken. The lump is sent to a pathologist who makes multiple slides to look at under a microscope. The advantage of this is that it can generally be done under local anesthetic, and is much more likely to get a diagnosis (now I have let you have a slice of the pie). The disadvantage is that if the mass is malignant, you still have to go back again to remove it. It is also more expensive than a FNA.
Now, given those 3 options of diagnosing a lump, every case is different and I would not recommend the same thing for every cat. It really does depend on what the lump looks like AND the rest of the physical exam findings. I would suggest a check up for your cat to have this examined in the next couple of weeks, or sooner if she has any other symptoms of illness (lethargy, loss of appetite, discharge from the bump).
If this has been helpful, please accept my answer and leave feedback. I will still be here to provide more information if you need it!
The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.
Fiona
Cat Veterinarian
Small animal medicine and surgery - 15 years experience in BC, California and Ontario