Clinical interest of lipomas in dogs
Lipomas in dogs are benign tumours that generally have no bearing on the animal’s health, but they are often a source of alarm for owners.1,2
Introduction
Lipomas are masses of mesenchymal origin formed by adipocytes.1,2 They are one of the most frequently diagnosed benign tumours by primary care vets. A study conducted in Switzerland showed that lipomas are the second-most common skin neoplasm in dogs after mast cell tumours.3 Furthermore, lipomas were the most commonly reported disease in a large scale survey of pedigree dog owners in the United Kingdom.4
It has been suggested that lipomas in dogs may involve a genetic component and that certain breeds, (Weimaraner, Doberman, Pointer, Springer Spaniel, Labrador, Beagle, Miniature Schnauzer and Cocker Spaniel) appear to be more predisposed; while they seem to be less common in other breeds (Yorkshire Terrier, Lhasa Apso, German Shepherd, Shih Tzu, Chihuahua, Cavalier King Charles Spaniel, West Highland White Terrier, Bichon, Jack Russell Terrier, Staffordshire Bull Terrier and Boxer).
Lipomas in dogs tend to become more prevalent with age. Dogs aged 9–12 years are 17 times more likely to develop a lipoma than those under 3.
Sterilised dogs that are obese or overweight are also apparently more predisposed to lipomas. 1
Clinical features of lipoma in dogs
There are three morphological types of lipoma in dogs: regular or “classic”, intermuscular and infiltrative.
On the other hand, variants such as angiolipoma, angiofibrolipoma and fusiform cell lipoma have been described from a histological perspective.5,6
Furthermore, lipomas must be differentiated from liposarcomas (rare malignant neoplasms originating from lipoblasts and lipocytes), based on their morphology, tomographic findings and histological characteristics.
As many as 98% of “classic” lipomas are located in the subcutaneous tissue,7 and rarely produce clinical signs.5 However, lipomas can be found in virtually any location. In fact, cases of lipomas in dogs have been described in the thoracic, abdominal, spinal, vulvar, vaginal, intrapericardial, intracardiac, pulmonary and bone cavities.5 They usually cause symptoms in these cases, mainly due to their compressive effect at local level, tissue constriction or compromised function of the affected organ.5
- Intermuscular lipomas are a variant of subcutaneous lipomas and are located between the muscle bellies. The most frequent location of this type of lipoma in dogs is the hindlimb, between the semimembranosus and semitendinosus muscles, but they can also appear in the axillary region. From a clinical point of view, they can usually be observed as firm, slow-growing masses.5
- Infiltrative lipomas are rare. These tumours are formed by well-differentiated adipocytes with no signs of anaplasia and look similar to “classic” lipomas in cytology and small biopsy specimens. In fact, they are considered benign tumours and do not metastasise. However, they are locally infiltrative and invade adjacent tissues. They can affect muscle, fascia, nerves, myocardium, joint capsules or even bone, depending on their location.5
Diagnosis
- Most lipomas in dogs are initially diagnosed based on the results of fine needle aspiration cytology.2,5
- They usually appear on an ultrasound as oval, well-defined, encapsulated, striated masses.8 To plan the correct treatment for a suspected infiltrative lipoma, it is important to define the size of the tumour and differentiate it from a conventional lipoma. Computed tomography is advisable for this purpose. However, differentiation is not always easy.5,9
Treatment
- “Classic” lipomas that course without any clinical signs do not require treatment, and their growth simply needs to be monitored.
- Surgical treatment is recommended for symptomatic masses or which interfere with the normal function of an organ, and this is usually curative in most cases, although local recurrences have been reported.2,5
- Other therapeutic options for these tumours include liposuction and intralesional injection of triamcinolone acetonide 40 mg/mL (0.5–1 mL, depending on tumour size).10,11
- Surgery is recommended for intermuscular lipomas, with the placement of drainage to prevent the formation of seromas. The postoperative prognosis is generally excellent.5
- Finally, aggressive surgical treatment is recommended for infiltrative lipomas, possibly with amputation of the limb depending on tumour location. Both partial and complete remission have been reported with radiation therapy.5
Conclusions
Worried owners often bring their dogs to the veterinary clinic because they have noticed a “lump under the skin” when playing. In many cases, these masses are lipomas and are not very serious. However, we should never ignore the importance of making the most accurate diagnosis possible. In most cases, the cytological study of samples obtained by fine needle aspiration can be used to confirm the presence of a lipoma or another process requiring other measures.
