Skin Masses

ask a vet, ask a vet a question, dog health issues, dog skin massSkin lumps and masses are one of the most common problems we see as veterinarians.  There are many different types of skin masses, some benign and many malignant.  Below is an example question from a pet owner who found a lump on her dog late and night after her veterinarian was closed.

Question by Carol B on 2011-03-09 11:36pm

Dear Vet Live, I am a business associate of Dr. Jed and Dr. Laci. We have met at a BlogPaws event and we work together on social media things. I now have a question about my dog and want to utilize this service, as I just discovered a “lump” on my dog’s paw.
Having had a dog with mast cell tumor stage II in the past, I am a diligent dog mom and want all lumps I find on my dog examined. I just discovered this “lump” while scratching/rubbing him tonight. It is about the size of a pea, appears under the skin and nothing protruding through to the surface. It is located on the upper part of his back rear paw, not near the toes, but on the anterior side about half way up. No redness, discharge and no discomfort to my dog on touching it. It is very moveable. It actually feels like a small moveable pea under his skin.
Of course, I am very concerned with any lump. Our vet is 2-1/2 hours away, and I thought to use your service first. I do realize any lump should be examined and looked at, possibly aspirated by the vet. If there is anything you can do to ease my mind tonight, that’d be most appreciated.
What could this be in a dog of his breed/age, etc? I checked his lymph nodes best as a lay person like myself can and feel no swelling to my touch. He eats, drinks, is active, has great bowel movement, is spunky and showing no other signs of problems. He last saw the vet for a checkup in December of 2010 and all was well.

response by Dr. Jed Schaible on 2011-03-09 11:42pm

Hi Carol,  I have some info for you in regards to Dexter’s Lump:

Dexter, like every dog and breed of dog should be considered as a potential risk for mast cell tumors (MCT). I have pretty much diagnosed MCTs in practically all breeds.

A pea-sized nodule under the skin could be many things. You are right in saying that it DEFINITELY should be checked out. Get the sample taken at your vet and get it sent to a lab rather than done in-house. In the case of MCTs, I wouldn’t be as concerned with them missing the diagnosis of a MCT (because they are pretty distinctive), but rather missing some other potentially bad diagnosis.

Given that Dexter is not a Boston, English Bulldog, Dachshund, pug, etc. (see attached handout), I would hope that it is likely not a MCT. But, lets not get ahead of ourselves:

My list of deferential would be the following (in no particular order):

Histeocytoma: benign tumors that are most common in young dogs and appear as round, reddish-pink, lack-of-hair nodules. Treatment is not usually needed because these lesions commonly spontaneously regress in 1-2 months.
Keratoacanthomas – also benign tumors of young dogs
Melinomas- less likely
Papillomas – In puppies these lesions are caused by a virus, but the cause in older dogs is unknown
Sebacous gland adenomas and adenocarcinomas – they develop from the epithelium of sebaceous glands. This is more common in older dogs.
Tissue reaction/allergy/foreign body : he could have a splinter or something that got walled off
Insect bite that caused a granuloma
Lipoma: if it is movable and small and soft (but not necessarily 100%) it could be a fatty benign tumor
Other neoplasia (I could go on and on but Dexter younger, so it is less likely)
Etc. ect… the tests need to be done to determine the cause

I know you are worried about MCTs. Mast cell tumors are the most common type of skin tumor in dogs. They can cause systemic signs because they can release heparin histamine, and other types of body chemicals that can cause problems. The good news is that approximately half of canine mast cell tumors are benign. If it is a MCT, those that are located in the genital area/ butt area/ penile area, or on the end of the limbs are more likely to spread to other tissues.

I wouldn’t start to freak out. Given that Dexter is younger and you are a vigilant parent, I would think that you would find his lump way before there would be lymph node involvement. If it is a MCT, the earlier and smaller it is detected, the better chance for cure. I have cured more MCTs than I have not (by a huge margin). So, stop worrying (probably not possible) and realize that you need to follow this plan:

Make an appointment for your vet to do a fine needle aspirate. Try to get an appointment ASAP. Tell them the situation and that you want a mass evaluated so and they may recommend a drop off or an appointment followed by a dropoff. I would prefer the later so you can talk to the doctor. I would also want to know that the cytology would be sent out to a diagnostic lab. I always made two sets of slides and did in house cytology on my own and had back up with a pathology lab. Cytology is dependent on the ability of the person who is looking under the microscope to make a diagnosis. Do not accept “lets keep an eye on it” ever. Get the test done and get them to send it out. There are so many things that can happen with the sample if it is read in-house by a vet that doesn’t do that too often. It is okay to ask them to have a board certified pathologist to read the sample too. It takes a few days so you can also ask for both. If it is a lipoma, you will get an answer really quickly (depending on their protocol for reporting results to pet owners). It won’t be much more money for a pathologist and that is what I would do.

One more thing. With skin lumps that could potentially be a MCT, you want to be sure that the vet pre-medicates with Benadryl (diphenhydramine) to prevent the procedure from causing a reaction from histamine release (histamine can be released from MCTs if they are messed with). Potentially your vet might look at it and feel it and say it is not necessary because they have ruled out the probability of MCT, but if MCT is on the list of diagnostic differentials, that should be done 10-20 minutes before the aspiration procedure (before the needle goes in). It is really safe, so I do it in all cases of aspiration where MCT might be be on the list- even remotely. MCT aspiration without premedication can cause anaphylactic shock in the most extreme cases.

There is no need to freak out. I attached a handout on MCTs but only so you can get more info. I don’t want to keep you waiting so I will send this over now. I am sorry for the delay- these are written from scratch and since you are a writer, you know… Let me know if you have more questions

My best,
Dr. Jed

File Uploaded: click here to view.

response by Carol B on 2011-03-10 12:14:22
Thanks for everything. We’ve known our vet 15 years and travel as far as we do to see him, and I am going to mention everything you said. Dexter’s lump is located right by his ankle bone; in fact, I almost thought it was his ankle bone. It is very moveable. I am calling tomorrow to get an appointment. TY for everything. This is a wonderful service, and I am glad I got to know you two.

response by Dr. Jed Schaible on 2011-03-09 12:15:36
Right back at you. I am happy to have helped you. You sound like one of the best pet owners out there. You can send me an update and questions about the lump via email. Give Dexter a hug for me. You have a great night!
Dr. Jed