Skin Lumps and Bumps: some basic definitions

Orange Villa Veterinary

archived newsletter article:

Skin Lumps and Bumps: some basic definitions

Many times a pet is brought in for examination of a new lump or bump. This can be very scary for some pet owners, as they always fear the "Big C"…cancer. Hopefully this article will help you to understand what some of the lumps and bumps are, what tests need to be performed, and what might need to be about them.

Fortunately for our pets, their fur helps to protect them against cellular damage from the sun. For that reason, skin cancer is not as common in pets as it is in sun-worshiping humans. Most lumps and bumps found on our pets are not cancerous. But some are.

First of all, what causes a lump? A lump is caused by an accumulation of something under the skin. This could be water, blood, serum, pus, gland discharge, or cells. If it is cells, it is called a growth. Growths can be benign (not cancerous) or malignant (cancerous).

If you see a lump, the first step is bringing it to the doctor's attention. This is especially urgent if the bump is growing quickly, is painful, bleeding, or your pet is licking at it.

During the examination, we will want to know about the lump:

Has you pet ever had a lumps before? If so, where? Were any removed?
How long has the lump been there?
Has the lump grown in size since you've noticed it? Any change is color or character?
Has your pet noticed the lump? Are they licking at it?
Have there been any bites, injections, or medications in that spot?
Are there other lumps you have noticed?
Is you pet's health otherwise normal? No lethargy, vomiting, diarrhea, weight loss, or restlessness?

Next a complete physical will be performed. Usually the lump will be looked at last. This physical is to check for other underlying diseases as well as to check for more lumps. Lumps can be difficult to find during the exam, especially if your pet has a lot of fur or is uncooperative. Sometimes marking the spots of the lump(s) at home with a non-toxic pen or nail polish is very helpful. The lump itself will be carefully examined and if small, measured as well. Sometimes a picture will be taken for comparison at a later date.

The next step is usually a fine needle aspiration. This entails sticking a very small needle into the lump and pulling out a few cells to look at under the microscope. Sometimes a diagnosis can be immediate. Some lumps we will want to send in the slide for a pathologist to evaluate. A pathologist is a veterinarian who specializes at looking at cells under the microscope. This can take a few days. Some lumps are easy to get a good aspirate to figure out what it is…with other lumps the cells do not fall into the needle easily, making diagnosis more of a challenge.

Once the examination and aspiration are performed, a plan is discussed. For some lumps, your pet will be sent home with instructions to watch the lump very carefully. This means making sure the lump does not enlarge, change colors, or change character (such as hard to soft, soft to hard, flat to round, etc.) If it does any of these things, you must come back right away. Sometimes a re-check by the doctor will be recommended in a few weeks.

For other lumps, removal might be recommended. This could be if we feel the lump is serious, we just can't tell what it is, if your pet's lump is changing at all, your pet is licking at it, or the groomer keeps hitting it. Generally, if the lump is removed, it is sent in for biopsy. A biopsy is a process where the tissue is sent in to the pathologist and cut into tiny sections to look at under the microscope. It is a much more reliable and accurate test than an aspiration. This is because biopsy gives a lot more information, such as architecture and margins. It would be akin to figuring out the style of a room, with biopsy looking at the whole room, and aspiration looking at a few pieces of furniture out on the lawn.

Some types of lumps:

After an aspiration and/or a biopsy, we can usually tell specifically what the lump is being caused by. Here are some definitions you may hear:

Hematoma: This is a collection of blood. Common in the ears, but can occur anywhere. Usually these are from trauma or a blood clotting disorder. These may require surgical treatment depending on severity and location.

Seroma: a collection of fluid under the skin. These are associated with resolving trauma or inflammation such as vaccination. Sometimes require surgical treatment.

Abscess: a collection of pus under the skin. This is usually from trauma such as bite wounds and foreign material under/in the skin. Abscesses and other skin infections can be secondary to severe allergies as well. If an abscess, sometimes the fluid will be submitted for culture. Usually require surgical treatment.

Hives/urticaria: These are from an allergic reaction, especially insects. They come on quite suddenly, usually several bumps that weren't present even an hour before. Generally respond to medication and identification of the cause.

Sebaceous cyst: an accumulation of secretions from a gland in the skin. These are very common. The gland overproduces a substance. Sometimes these cysts can get so big they rupture, causing pain and inflammation. Sometimes they come and go away on their own. If the gland tissue is not removed, they generally come back with time.

Tumors: Tumors occur when certain types of cells keep reproducing more than normal. Benign tumors are not cancerous, Malignant tumors are cancerous and grow out of control. They are quite aggressive and can spread elsewhere in the body (metastasis). Some benign tumors can later become malignant. Also, just because a tumor is benign does not mean it can't cause problems. Some benign tumors can secrete toxic substances or become so large that they interfere with proper movement.

There are a great many types of benign tumors, too many to mention. One of the most common benign tumors is called a lipoma or fatty tumor.

Lipomas are composed of fat cells. They are soft and lie underneath the skin. They can be any size and anywhere on the body, but most common on the belly and chest. They are very common in older dogs and quite rare in cats. Small lipomas are generally watched if they are just under the skin. If they enlarge at all, removal is recommended. Lipomas, although benign, can get enormous. They can get so big they start to interfere with normal body function, such as walking. Lipomas, if they develop under the muscle are called infiltrative lipomas. Due to the involvement of the muscle they can be very painful. They need to be removed right away. Lipomas are generally diagnosed by needle aspirate. In very rare cases a malignant form, called a liposarcoma can be present. These require surgery to remove. If a lipoma is growing quickly-it needs to be removed and biopsied right away.

There are a great many malignant tumors as well. The following is a list of some of those tumors:

Mast Cell Tumor: A tumor comprised of a type of immune cell called a Mast Cell. These tumors can be quite dangerous for a few reasons. Some can metastasize (spread) elsewhere in the body (in the skin or an internal organ). All can be very aggressive locally and the actual tumor is much larger than the lump you can see and feel. These tumors also produce chemicals, such as histamine which can cause severe itching, allergic reaction, even vomiting and stomach/intestinal ulcers. The can mimic lipomas but are usually very easy to identify on aspiration. If a mast cell tumor is found, immediate surgery and biopsy is advised. The biopsy will help determine whether more surgery or medications will be needed.

Squamous Cell Carcinoma: These occur commonly on areas of light skin/little fur such as the stomach of boxers and Dalmatians, and the ear tips and noses of white outdoor cats. It is thought they occur secondary to sun damage. They generally do not metastasize from these locations but can be very aggressive locally. In the mouth, these tumors are much more aggressive and can metastasize. The earlier surgery is performed, the less disfigurement from removal occurs. Sometimes laser surgery or radiation is recommended.

Melanomas: These tumors are much less common in pets than people. These come from cells which produce the pigment (color) to the skin. The tumors are generally (but not always) dark in color and common on darker skinned animals. The can be benign or malignant. Aspiration can commonly identify a melanoma but not benign vs. malignant. Biopsy is always advised. If these tumors are on the feet or mouth, they are much more aggressive.

Mammary gland tumor: While not technically a skin tumor, these tumors can be felt on the abdominal skin. Much more common in dogs than cats, and much, much more common in females than males, these tumors arrive from the mammary tissue (breast). Dogs have 10 nipples typically, and therefore can have multiple tumors. These tumors are about 50/50 benign and malignant, and with time benign tumors can transform into malignant ones. They generally feel like pellets or peas under the skin next to the nipples. These tumors can be locally aggressive and highly metastatic-to local lymph nodes or the lungs. Generally chest X-Rays are always performed before surgery. Sometimes medication is recommended after removal if spread is suspected. This is one of the few preventable tumors. Spaying your dog before she goes into heat is almost 100% effective in preventing these tumors. Spaying after the 1st and before the 2nd can also be helpful (about 70%). After that, there is little statistical difference between intact and spayed dogs.

Lymphoma: This is a disease of a type of white blood cell called a lymphocyte. It can occur anywhere in the body. Usually, it is in a form called multicentric, and it causes very hard swellings of the lymph nodes, which are under the skin. This form of lymphoma is diagnosed with aspiration. There is also a skin form. This form of lymphoma is called "the great mimicker" because it can look like many other forms of skin disease, such as a simple skin infection. Diagnosis is generally skin biopsy because the area did not respond to conventional medications. Frequently, pets with lymphoma are also quite ill, which is different from other causes of lumps. Lymphoma is one of the few tumors that respond very well to medications. Generally, the more medications that are used for lymphoma, the greater the survival time. Unfortunately, surgery is rarely a treatment option for these pets. Just because your pet has lymphoma and is feeling fine is no reason not to treat. In fact, pets that are not sick from their lymphoma do much better and lead longer, healthier, happier lives than those that are sick on diagnosis.

Fibrosarcomas: These tumors arise from connective tissue. They can be very aggressive locally but tend not to metastasize. One cause of fibrosarcomas is secondary to a responsive from inflammation of any type, such as healing from an injury, chronic infection, or an injection-reaction (more common in cats than dogs.) There is a subset of fibrosarcomas in cats called vaccine-induced sarcomas, which is thought to be secondary to vaccination from Rabies or Feline Leukemia. Luckily, these tumors are rare (less than 1:4000 cats vaccinated). Prompt attention is needed, because if these tumors get too big, removal is very difficult. For this reason, the leukemia vaccine is given at the left ankle (back leg) and the rabies in the right. If you feel a lump in this area, bring your cat in immediately. Fibrosarcomas in dogs and cats do not aspirate well, as the cells don't fall into the needle as well. Usually they are quite firm and under the skin. Biopsy is usually required for diagnosis.

Hopefully this article helped you to understand some of the lumps and bumps your pets can have. It was not intended to scare you, but rather to let you know the importance of regularly checking your pet for lumps and bringing them to our attention. Remember that proper vigilance and quick response can save your pet, even from some really nasty cancers.

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