Medically reviewed by: Kinga Wojtczak, Doctor of Veterinary Medicine, specialist in canine and feline diseases
How does a lipoma in a dog form? Is it dangerous? Do the tumors have to be removed? In this article, we will take a close look at lipomas in dogs.
Asked what the lesion on the side of their dog's body is, owners very often tell me "it's just a lipoma." But is every lipoma really "just a lipoma"? No lesion should be ignored, even if it seems benign and is not getting bigger.
Lipomas in dogs are most often found in the subcutaneous tissue (the layer under the skin), on these parts of the pet's body:
- on the sides of the chest,
- in the groin,
- near the limbs.
Lipomas in dogs are tumors classified as benign, with a low potential to metastasize (spread). Sometimes, however, the size and location of a lipoma in the subcutaneous tissue significantly interfere with the dog's functioning. Very often, though not always, a lipoma is associated with:
- increased body weight,
- thyroid problems (most often hypothyroidism in dogs),
- Cushing's disease
- the dog being middle-aged or a senior.
Table of contents:
What is a lipoma in dogs?
As I mentioned above, the term "lipoma" describes benign tumors.
Predisposition to lipomas
Middle-aged and older animals struggling with obesity are particularly predisposed to this type of tumor.
Dog breeds in which lipomas are seen particularly often are:
- Labradors, Golden Retrievers,
- German Shepherds,
- Shetland Sheepdogs,
- Dachshunds,
- Cocker Spaniels,
- Weimaraners,
- Schnauzers,
- Beagles.
Symptoms of lipoma in dogs
A lipoma in a dog does not metastasize to distant solid (parenchymal) organs. These tumors are usually well formed and compact; the masses sit in a connective tissue capsule that is well demarcated from the surrounding tissues. Lipomas are generally slightly firmer than the subcutaneous tissue and clearly demarcated from it. They are not very firmly attached to the underlying tissue, and very often the tumors move easily under the skin, to which they may be attached.
However, some tumors infiltrate the surrounding tissues, and their capsule is not well formed. The tumor then tends to grow in strands into the surrounding muscles. Such forms are much harder to remove surgically, and you need to be aware that the surgery carries a high risk of failure. In rare cases, the tumor develops into a malignant form called liposarcoma. At that point the lesion is a malignant tumor that may metastasize to distant tissues of the body. It also requires urgent surgical intervention and adjuvant therapy.
Unfortunately, as with most tumors, the causes of lipomas are not fully understood. It is believed that a combination of environmental conditions and genetic predisposition influences whether the lesion develops. Another theory holds that this tumor forms as the body's defense against some irritating stimulus that persists for a long time, for example a poorly fitted harness or an uncomfortable mattress to lie on.
Diagnosing lipomas
Diagnosis of a suspicious lesion is based primarily on a fine-needle aspiration (FNA). This method is safe, causes little pain and gives a quick answer about the nature of the lump. The vet punctures the tumor with a thin needle, and the material collected this way is examined under a microscope.
In lipomas, the sample has low cellularity: mainly fat cells are seen, full of fat, and they may also be slightly deformed. If the result is not entirely conclusive, if the sample contains other cells, or if the person evaluating it is not sure of the diagnosis, an excisional biopsy should be performed. For these tumors, it involves removing the entire tumor with a small margin and sending the material obtained for histopathology. Further management (re-excision with wider margins or adjuvant therapy) depends on the histopathology result.
When should a lipoma be removed, and when should you wait?
Surgery should be performed by a vet without delay when growing tumors make it difficult for the animal to move. Lumps on the limbs, where the joints bend, or right by the neck should definitely be removed. A large tumor, or one located in the abdominal cavity, is also an indication for surgery: when the tumor presses on the internal organs, it may impair their function.
It is a good idea to opt for surgical treatment if the skin over the tumor is tight and stretched, or if bleeding or inflammation appears in that area because of the pressure of the mass on the skin. However, if the tumor is small and not growing, and of course if the diagnosis has been confirmed by a biopsy result, the surgery is not urgent.
Treatment of lipoma in dogs
The treatment of choice in dogs is surgical removal of the tumors and the abnormal tissue. As with any planned procedure, the patient should be carefully prepared. A blood test is absolutely essential. Lipomas usually affect older animals, so you should consult a cardiologist before the planned surgery. An echocardiogram (heart ultrasound) makes it possible to assess the patient's condition and choose the right anesthesia.
The lumps are surgically removed together with the capsule surrounding them. The surgeon often performs reconstructive surgery of the skin and subcutaneous tissue in the affected area: stretched, poorly elastic tissues can create a risk of what are known as "dead spaces," i.e., sites particularly prone to collecting fluid (exudate) or developing swelling after surgery. After properly performed surgery, when the entire tumor capsule has been removed, the risk of the mass coming back is rather low.
For large tumors, where the tissue loss is significant, a pressure bandage can help prevent inflammatory swelling in the surrounding tissues. The recovery period after surgery is usually no more than 14 days.
Infiltrative lipoma
The situation is completely different with infiltrative lipomas, which invade the surrounding tissues. In these cases, fragments of the connective tissue capsule penetrate between the fibers of the muscles under the tumor. Sometimes the muscle fasciae, tendons, blood vessels, nerves and joint capsules are also infiltrated by tumor cells. Among the dog breeds particularly predisposed to this form of lipoma are Labradors, especially middle-aged or older spayed females.
Unlike ordinary lipomas, dangerous infiltrative lipomas can be firmly attached to the underlying and surrounding tissues. They may cause the animal discomfort, itchy skin, lameness if they occur near the limbs, or paralysis of a nerve close to where they are located. Their size also varies: they may be small lesions, or they may grow large.
Removing such tissue completely is very difficult and requires careful surgical planning, and because the tumor infiltrates structures vital to the body, it is sometimes outright impossible. It is important to try to remove the tumor completely, because only that approach guarantees full success of the surgery. Otherwise, if not all of the tumor cells have been removed, the infiltrative lipoma may grow back.
Additional imaging can help in planning the treatment and the surgery: in complicated cases, an ultrasound of the affected area or a computed tomography (CT) scan of the animal's body is helpful. Imaging will help determine how the tumor's strands actually run, how deep and how far they reach, and how extensive the surgery should be.
Even then, knowing precisely where the affected tissue runs, it is not always possible to remove all of the affected areas completely. If part of the infiltrative lipoma is suspected to have been left behind, it is a good idea to use additional therapy.
Radiation therapy
The literature reports success with radiation therapy in dogs after incomplete resection of an infiltrative lipoma: in patients that received radiation therapy, no signs of recurrence had been observed after 40 months. Without adjuvant therapy, the recurrence rate is high. It is estimated that in as many as 60% of animals, the cancer recurs within 16 months of surgery.
Prognosis
With complete resection, when the whole tumor mass is removed together with its capsule, the prognosis is good. These tumors rarely grow back on the skin in the same places, but they may appear in other parts of the animal's body. The situation is different with incomplete resection, when some of the cells are left behind. In such cases, the risk that the lipoma will come back is very high. As I mentioned, it is then a good idea to use additional therapy to slow the growth of the tumor cells.
If the owner decides against surgical treatment, the lesions should be closely monitored. In the initial period, as soon as the lesion is noticed, it is a good idea to measure it regularly (for example, once a week), always in the same plane. If the lesion is seen to grow, it is a good idea to opt for surgical removal.
Can lipomas in dogs be prevented?
Unfortunately, there is no method that guarantees that your dog will never develop lipomas. Weight control seems to be the most sensible way to prevent them. A small amount of body fat and not letting the dog become obese will make it much less likely to develop these tumors. A well-balanced dog food that is low in simple carbohydrates, besides its general benefits for your pet's health, may also help inhibit the development of these tumors.
Above all, however, you must not ignore any lesion or tumor that suddenly appears on your pet's body. Every lump, thickening or bald patch the owner notices should be thoroughly diagnosed. A seemingly insignificant lesion may turn out to be a life-threatening tumor. That is why the word "lipoma" must not be overused when the diagnosis has not been definitively confirmed.
FAQ
What does a lipoma look like?
Tumors can appear gradually or suddenly, and there may be one tumor or several at the same time. The growth rate varies: they may stay the same size and volume for years, but the diameter of the tumors can also double or triple very quickly. Their size varies too, reaching up to a dozen or more centimeters in diameter. Lipomas in dogs most often appear in places where fat tissue is abundant, so we expect to find them under the skin, on a leg, and less often on the belly or in the abdominal cavity.
Are lipomas painful?
Lipomas in dogs are generally not painful, nor do they tend to rupture or ulcerate. However, this depends on where the tumors are located. As I mentioned, lipomas can reach impressive sizes, so when they are located near the limbs or joints, they can make it difficult for the dog to walk and keep its balance. Sometimes constant irritation of the skin, or of the skin bulging over the tumor beneath it, may cause signs such as local inflammation and discomfort for your pet.
Where do lipomas most often appear in dogs?
Lipomas in dogs most often appear in places where fat tissue is abundant.
Which dogs are predisposed to these tumors?
Dog breeds in which lipomas are seen particularly often are: Labradors, Golden Retrievers, German Shepherds, Shetland Sheepdogs, Dachshunds, Cocker Spaniels, Weimaraners, Schnauzers, Beagles.
