Histiocytoma: Rio's Mysterious Bump

by  Krista Magnifico, DVM

Rio is a Belgian Shepherd. He may look rather ominous, but he is rather small and lithe under his long luxurious coat and serious face. His ears stand straight up and did so at a very early age, (for the German Shepherds this can be a long and somewhat frustrating task that keeps us guessing as to when and if they really will ever stay up?).

Rio was adopted as an early Christmas present to his parents from each other. 

He arrived off the plane as a tiny bundle of ebony fur complete with Santa hat. He, like every puppy that enters a home after the departure of a pet who has passed away from old age and disease, seemed like (and was) a bolt and jolt of lightning. Their previous decade of caring for a well-trained, sedate, courteous adult dog became a life that quickly required baby proofing the home, the trials and tribulations of housebreaking (always made significantly more difficult when attempted in the middle of a record awful winter), the in home gymnastics and calisthenics when it’s too cold and snowy outside to burn off steam, and teething. For a retired couple I answer a lot of questions, but most of them include a few affirmations that “yes, this is normal puppy behavior.” Followed quickly by the sworn testimony of the pleadings that their last dog was “never this wild,, high strung,,, hard to train,, crazy,, loud,, mouthy,, bite-y,, playful,, hungry,, etc. etc..

Rio was always a very smart, rambunctious, and happy puppy. 

He was housebroken in a few weeks and continues to grow exactly on schedule with an excellent daily regimen of excellent diet, exercise plan, and good puppy manners training. I saw him exactly on schedule for every needed check-up, vaccination, and miscellaneous puppy question.

But at his 3 month old puppy exam his parents mentioned to me that they were concerned about a bump on his nose. 

January 22, 2014

Understanding bumps and being able to categorize them by sight takes years. You see, “lumps and bumps” can come from too many things that can resemble each other, and come from various etiologies. Some are benign cosmetic bumps, and some are potentially life threatening tumors that need to be addressed quickly. So when it comes to trying to figure out which is which is where your vet is an invaluable resource.

Lesson Learned: Pay attention to bumps, lumps, and skin abnormalities immediately by asking your vet about them! Also, follow their recommendations for diagnosing and treating them. If they feel a biopsy, aspiration, or medical treatment plan is indicated I encourage you to listen, AND, follow up with all recommended re-checks.

Of course, Rio's parents were worried about the following:
  1. Was it a dangerous bump? (We use the word lesion).
  2. Could it be treated so it would go away soon? (It is after all ugly).
  3. Was there something we could put on it to keep it from bleeding, or rupturing, or getting infected?
  4. What caused it?
  5. Will he get more?

I did not believe that it was a dangerous bump because
  1. He is soo young
  2. It came up so quickly
  3. It wasn’t bothering him at all
  4. I thought I knew what it was

Treatment relies on diagnosis in many cases. 

It is far safer, and more effective to treat a lesion IF we know what it is. And, his is on his nose, and anything that you put there will be immediately licked off, so I would have to give him a medication that is effective AND safe to ingest. (Boy does that limit your options!)

A bump or lesion will rupture and bleed when it gets too big for the overlying skin to keep closed.

The only way to avoid this is to have it removed or treat it so that it shrinks before this happens. Infection occurs with an open draining wound, OR a mass that is beneath the skin. We don’t commonly see infection with masses that are from the skin.

What caused it can be explained when the lesion is diagnosed.

All of this leads me to giving you some hints about what I suspected Rio’s bump was.

Rio’s clues were;
  1. Age on onset, 3 months.
  2. Character of lesion; spontaneous eruption and regression.
  3. Size and shape, small round, raised, erythematous (red) singular.
  4. Non-painful.
  5. Area of body affected.

January 28, 2014

I explained to Rio’s parents that like every diagnosis in medicine the only definitive way to correctly diagnose a lump or bump was to remove (or take a sample) of tissue and examine it at the microscopic level.

Without doing this we were making a presumptive diagnosis. 

Sometimes we skip this step based on cost to run the confirmatory pathology tests, time constraints of patient health (say for example a bleeding intra-abdominal mass that needs to be removed immediately so the patient doesn’t bleed to death while we wait for a pathology report), a response to treatment that indicates a diagnosis, or even a good educated guess on your veterinarians part.

But definitive diagnosis should always be made by a biopsy, guessing, whether well-educated or not, is still guessing. 

Rio’s lesion was about a quarter of an inch, or about a half of a centimeter, and right beside his nose. This left either removing it with surgery, or trying to get an impression smear with a glass slide. Now Rio is a bouncy boy who prefers to be lunging at your face to kiss you then be expected to hold still. He is also about three months old. We decided to take my presumptive guess as a diagnosis and IF the lesion worsened or grew we would remove it for biopsy at the time of his neuter, which we could do early if needed.

January 30, 2014
My presumptive diagnosis was that Rio had a histiocytoma. 

“A histiocytoma is a common but benign tumor affecting the skin. Their cause is unknown but believed to be a consequence of proliferative or reactive hyperplastic Langerhans cells (these type of cells overpopulate without known cause) but are not truly considered neoplastic (cancerous).

They are most commonly seen in young dogs under age 2. They are usually solitary and found on the head, ears, and limbs. They are usually less than 3 cm in diameter, firm, dome, or button shaped, well circumscribed, dermal in location, and frequently ulcerated. They are fast growing but benign. Diagnosis is based on cytological examination.” (Edited from Muller & Kirk's Small Animal Dermatology, 6th edition).

Our plan was to monitor the lesion closely and come in for weekly re-checks.

It has been a little over 8 weeks and the bump is gone. 

A small hairless area remains but I expect this to fill in normally over the next few weeks. I also expect that there will never be even the tiniest hint that the bump was ever there at all by then.

February 18, 2014
If you have any lump, bump, or any thing in between,pet question, you can find me and a whole bunch of other helpful people at Pawbly.com. We are the best place to share information, exchange pet photos, meet people with similar pet interests, and join the pet social network to help pets around the world!

Or you can find me on Twitter @FreePetAdvice, or at the veterinary clinic, Jarrettsville Vet, in Jarrettsville Maryland.


Krista Magnifico, DVM owns a small animal hospital in northern Maryland, where she practices everyday. She wants to make quality veterinary care available to everyone, everywhere at any time; trying to save the world 1 wet nose @ a time.  Her blog is a diary of he day-to-day life & the animals and people she meets. 

Dr. Krista is also the founder of pawbly.com, free pet advice and assistance.

To contact her, you may leave a comment on her blog, email her or catch her on Twitter or Facebook.

Articles by Dr. Magnifico:
Don't Make This Mistake: Ruby's Death To Heat Stroke 
Parvo: Cora's Story 
Jake's Laryngeal Paralysis
The Tip Of The Iceberg: The Unexpected Dental Dilemma
The Ear Ache That Wasn't Going Away: Tottsie's Story
Cody's Eyelid Tumor
Ruger's Mysterious Illness
The Day The Heart Stood Still: Timber's Story 
Different Definition Of Comfort Food: Levi's Story 
Savannah's Pancreatitis 


  1. That's great, I believe my pup was diagnosed with this. The vet gave me two options: cut it out or use a steroid cream. He suggested I rub the cream in well so that when my pup licks it then he will still have gotten some medication. My concern is that he keeps bumping it and it bleeds often.

    1. If it's causing trouble, it might be best to remove it.

  2. The writes IS a vet. However, you could talk to your vet about OTC alternatives or script to your pharmacy.

  3. My puppy has a histiocystoma on his back and he is a black lab hound mix, he has had it for about a month and it keeps bleeding and getting bigger. We went to the vet about a week ago and the tests confirmed it is a histiocystoma but it doesn't seem to be getting any better. How long should we wait to see if we should remove it?

    1. Well, while I always lead toward non-invasive solutions, this does sound like something I would want to take care of surgically. It's active, it's ulcerating, bleeding ... I'd go back to the vet, repeat the aspirate and get it out.

  4. My dog just got something like this on her foot, totally out of nowhere, just saw her licking it. She is 6, do they happen in middle age dogs?

    1. It is more likely in younger dogs. Here is the thing - it could be histiocytoma, it could be an interdigital cyst or it could be a mast cell tumor. Please have it checked and aspirated.

  5. Went to the vet she just looked at it (no aspiration) and said she thought it was cyst that was infected.

    1. Interdigital cyst is certainly a possibility. What did she recommend to treat? Epsom salt soaks might help but there could be a foreign body in there somewhere.

  6. It isn't quite in between the toes it is more on the upper part of the paw. She recommended aloe vera gel and neosporine and cover with a sock. And check back if it doesn't get smaller.

  7. A red bump popped up on my dogs ear out of nowhere it seems. I called his vet and tried to discribe it and they said I could bring him in or try putting neosporin on it and watching it. Being it wasn't bothering him we went with the latter. It's been a month. I've kept it clean and kept ointment on it and the entire time I've been researching. From pictures and descriptions online it's a Histiocytoma. The problem is he finally either scratched it or it ruptured on it's own. Looks gross but he still isn't bothered at all. Is it safe to just continue cleaning it and applying neosporin until it's gone? It's kind of just open and crusty right now.

    1. Well, they can ulcerate and get infected. Have it checked and aspirated.


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