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Mesenchymal tumor

Species: Dog
Breed: Terrier mix
Age: 5-8 years
Need some input. My dog (she's 6)had developed a small lump/bump on her head above left eyelid. It's about the size of a pea and feels like its in the skin. Took her to vet and they said to just watch it, could be a bug bite. If doesn't get better bring back to have it removed.

A month later, it's still there. Went to a different vet and they did a FNA. Results were inconclusive, but suspicious for mesenchymal tumor. We have surgery scheduled for removal next week.

My concern is that the cells from the FNA were damaged, which lead to this suspicious report.

Could it still be benign? Today Vet mentioned fibrosarcoma or mast cell as possibilities. I'm a mess and just looking for some more information.

The lump:
Does not bother her
No color to lump, it's in skin
No loss of hair at site
Size of a pea
Moveable, inside skin

Do you feel that this FNA cytology report (which I am emailing as I can't attach to this) still can be benign. I have researched cytology reports and my head is spinning.

I've come to the conclusion that it can be anything from a benign fibroma to a malignant fibrosarcoma.

I know I will know for sure after the surgery and the pathology report comes back. Just wondering if there was any additional information, input or guessed that you mAy have
Do you have any further insight?


Online vet, Dr. Marie

Dr. Marie replied:

Thank you for sending me a copy of the cytology report. That really helps:

cytology report

A mesenchymal tumor is one that arises from cells in the connective tissue. There are many different kinds, some of which are quite serious and some of which are completely benign.

The fact that the cytologist is recognizing these cells as mesenchymal means that they're not just normal skin cells. There is definitely some type of growth process there. However, it is often hard on a fine needle aspirate (even if the cells weren't broken) to determine whether this is cancerous or not.

One cancerous possibility is that this could be a fibrosarcoma. Fibrosarcomas are often treatable if they can be completely removed. Given that this is a small lump, there's a great chance that it can be completely removed. As fibrosarcomas grow, they can start to infiltrate into muscle and between muscle layers and get very difficult to remove completely. These are the cases where I worry. But, a pea sized tumor means that even if it is a fibrosarcoma then there is a good chance that it can be cured with surgery.

It could also be something called a fibroma which is a benign lump that will most definitely be cured with surgery.

A mast cell tumor is another type of mesenchymal tumor. Usually though, mast cell tumors are fairly obvious on cytology. The fact that the cytologist didn't suggest a mast cell tumor makes this less likely. But, if it was a mast cell tumor then there are different types. Some are quite benign and others can be quite serious.

There are other types of mesenchymal tumors as well. However, at this point it really is just a guess. The purpose of the fine needle aspirate was to tell us whether surgery was necessary. So, now we now that this is a lump that needs to be removed as opposed to a minor cyst or wart or something like that. Once it is removed your vet will send the lump away and the results from the histopathology will give you more conclusive answers.

I know that waiting is hard. But, the fact that this is still a small lump is a really good sign.

I hope things work out ok.

Dr. Marie.



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Disclaimer: Although Dr. Marie is a qualified veterinarian, the information found on this site is not meant to replace the advice of your own veterinarian. AskAVetQuestion.com and Dr. Marie do not accept any responsibility for any loss, damage, injury, death, or disease which may arise from reliance on information contained on this site. Do not use information found on this site for diagnosing or treating your pet. Anything you read here is for information only.

Customer reply:

thank you Dr. Marie --
The waiting for the surgery and then the pathology will be hard. I did want to ask if trauma could cause the FNA of the lump to contain mesenchymal tissue. As if it were healing -etc. My dog did bump her head on the door running in from outside. We initially thought the bump was from that. I feel like it was a tiny bit bigger (maybe like a marble) when we first noticed it and then a week later when I took her to the Vet, it was the size of a pea.

Could there be any relation to this? We don't even know for sure if the bump/lump is from her banging her head - just trying to look back on the timeline.

Thank you.


Online vet, Dr. Marie

Dr. Marie replied:

It's very unlikely that the bump from the door caused this. We don't really know why these these come up but I can't say I have ever seen one that was caused by a trauma.

Dr. Marie



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Dr. MarieDr. Marie is a veterinarian who practices in a busy animal hospital in Ottawa, Ontario. She created Ask A Vet Question as a resource for good, accurate veterinary advice online. Dr. Marie treats dogs, cats, hamsters, guinea pigs, and rats. She has been a vet since 1999.

Is an online vet visit just as good as a trip to your veterinarian? No! But, many times, asking an online veterinarian a question can help save you money. While Dr. Marie can't officially diagnose your pet or prescribe medications, she can often advise you on whether a vet visit is necessary. You can also ask Dr. Marie for a second opinion on your pet's condition.