Abscess without open wound?

Hello vets, My 2 year old bloodhound Opey developed a large bump on his back Friday before last after about 30 minutes of playing outside. It didn’t feel soft or liquid filled, was just pretty hard. It’s not painful to him at all. Initially that Friday afternoon we gave him some Benadryl because we thought it could be a bee sting, but the Benadryl didn’t help at all. Since that Friday, the bump has gone down a bit in size but not gone away. We were able to get him into the vet yesterday where they did an FNA (fine needle aspiration) and they said it looks like it’s an abscess and it is filled with nutrophils. We paid to have the fluid they pulled off the lump (or abscess, I guess) sent out to be cultured to figure out what antibiotics would be needed and what this is, but I’m just confused and so is the vet. How did he develop an abscess without there being a wound there? They said it could be an infected bee sting or bug bite, but what they saw wasn’t the typical bacteria for that. They also didn’t feel it necessary to lance it because they were able to pull off almost all the fluid that was on it, but also because it had been going down in size and is not very big at all. Also, for background, July 1st he developed pneumonia so he just completed 2 20-day courses of antibiotics on July 21st (the lump appeared on the 23rd). They made this seem pretty nonchalant and like he just would need to finish these antibiotics, but then as we were leaving they said hopefully results show nothing really bad. What does that mean? Would could this be? I’m so worried about my boy!

Hello!  One thing that I, as a vet have learned from answering questions on this site, is how easily a passing comment like 'Hopefully it won't be anything bad,' possibly meant to reassure, can concern an owner.  You are not alone in this and it shows the importance of two-way communication between a client and vet.  Does your vet know how worried you are?

I don't know your vet and haven't seen your work-up so am not necessarily in a position to interpret their comment correctly, but I would take the comment to mean 'I don't think it's too bad but can't guarantee it at this stage.'   Good questions to increase your understanding may include:  Why do you think a healthy 2 year old dog got pneumonia in this case?  How common is this?  How would we know if it was something more complicated?   Etc.

Questions like this help to increase your understanding of the situation and will hopefully help to alleviate some of the confusion that you are feeling. Regarding your original question, it is not uncommon, for example, to find an abscess caused by a tiny foreign body eg an insect sting without a foreign body entry point.  Eg a splinter or thorn entering the skin, taking bacteria with them.  The immune system then wages war on the foreign body / bacteria but it might take a while for an abscess to form, by which time the entry point (which can be tiny and covered in hair) may no longer be visible.  Furthermore, miniature foreign bodies can migrate in the tissues, so the abscess can end up being miles away from the place it entered the skin.  It is not the only possibility and certainly not unusual for the initiating cause never to be found.

It sounds as though you have a thorough vet who has taken the trouble to check the kind of cell present in an abscess and send samples to the lab to check that they are using the correct antibiotics.  I can't tell you that there's nothing to worry about because I don't know enough about the case, but it is generally encouraging when a vet admits to being puzzled and looks for more information;  we don't always know the answers, but our training helps us to know what to do to find out.  Are you due for a recheck soon?  It may help to write down any questions you have, so that you know they will be covered in the consultation.