A lipoma is a very common benign mass made up exclusively of fat cells. While the vast majority of lipomas are located just under the skin anywhere in the body, these lumpy masses may also develop in the abdomen and chest.
About 16% of dogs are affected Middle-aged to geriatric dogs are most predisposed. Among these, obese adult female dogs are particularly at risk. Cats, on the other hand, are unlikely lipoma patients. Lipomas are considered rare among felines.
As benign masses, lipomas are not considered cancerous. As such, they do not metastasize (spread) to other tissues. They can, however, prove problematic in other ways, as when they grow large enough to interfere with normal movement or when these space-occupying masses arise in inconvenient anatomical locations.
As with so many other masses -- cancerous or otherwise -- the exact cause of lipomas is unknown. Because some breeds of dogs are overrepresented, some genetic influence can be assumed.
Symptoms and Identification
A lipoma will typically present initially as a small, hemispherical lump under a dog's skin. It will usually appear haired, relatively soft and somewhat mobile, though variations in texture (firmer masses that are more firmly adhered to the underlying tissues) are not uncommon.
Many dogs will present with multiple lipomas on their body at once.
While most lipomas are diagnosed via a fine-needle aspirate, it's important for owners to understand that a fine-needle aspirate is not always 100% accurate given that it only retrieves a small number of cells that may not be representative of the mass as a whole.
For that reason, dog owners are asked to monitor the mass for rapid growth or any changes in appearance or texture. Annual re-aspiration of these masses is typically indicated.
Since lipomas are rare in cats, the presence of any lump may represent a more sinister type of growth. Which is why some veterinarians believe the presence of any mass under the skin requires a biopsy, not just a fine-needle aspirate.
Since the vast majority of canine lipomas are harmless, surgical removal is only necessary if they are large enough to cause discomfort, hinder normal movement, or interfere with body functions. Nonetheless, biopsy (to retrieve a substantial sample of tissue) with or without surgical removal is strongly recommended for cats with fatty skin lumps.
If owners elect surgery for cosmetic reasons, they should understand that these masses can prove problematic post-operatively in that a higher risk of post-surgical complications (at the site of surgery) has been reported for these masses. For this reason, some veterinarians are now pioneering the use of liposuction to extract fatty tissue from within these masses. Unfortunately, re-growth rates following surgery or liposuction are high.
In addition to surgery and liposuction, steroid injections and laser therapy (among other alternative therapies for pets) have also been studied but no conclusive approach to handling all lipomas has been adopted by the wider veterinary community.
Rarely, a dog's lipoma will become locally invasive. In these cases, removal may be indicated and radiation therapy may be helpful in limiting its re-growth.
As benign masses most veterinarians elect not to routinely remove, lipomas are considered relatively inexpensive compared to other lumps. Their cost is typically confined to the price of the annual fine-needle aspirate, which usually costs anywhere from $20 to $100.
Surgical removal, however, can prove pricey -- especially given that these tumors have a high degree of post-op complications. Owners should expect to pay anywhere from $200 to $500 per mass. Should the mass be extremely large, reside in a hard-to-reach spot, or should it be highly invasive, surgical expenses may creep toward $1,000 -- more, should a board-certified surgeon be enlisted to remove a mass deemed especially difficult.
There is no known mode of prevention for lipomas. However, since they occur more frequently in overweight dogs, healthy weight maintenance should be of some benefit in limiting the size and/or number of lipomas.
Bergman PJ, Withrow SJ, Straw RC, Powers BE (1994) Infiltrative lipoma in dogs: 16 cases (1981-1992). J Am Vet Med Assoc 205: 322-4.
Bottcher P, Kluter S, Krastel D, Grevel V (2007) Liposuction-removal of giant lipomas for weight loss in a dog with severe hip osteoarthritis. JSAP 48: 46-48.
Case JB, MacPhail CM, Withrow SJ (2012) Anatomic distribution and clinical findings of intermuscular lipomas in 17 dogs (2005-2010). J Am Anim Hosp Assoc 48 ((4)) 245-9.
Goldman A, Wollina U (2009) Lipoma treatment with a subdermal Nd:YAG laser technique. Int J Dermatol 48: 1228-1232.
Goldsmith MH, Hendrick MJ (2003) Tumors of the skin and soft tissues. In: Meuten DJ editor: Tumors in domestic animals, Lowa State Press: Blackwell. pp. 45-117.
Hunt GB, Wong J, Kuan S (2011) Liposuction for removal of lipomas in 20 dogs. J Small Anim Practice 52: 419-425.
Mayhew PD, Brockman DJ (2002) Body cavity lipoma in six dogs. J Small Anim Pract 43: 177-181.
McChesney AE, Stephens LC, Lebel J, Snyder S, Ferguson HR (1980) Infiltrative lipoma in dogs. Vet Pathol 17: 316-322.
McEntee MC, Page RL, Mauldin GN, Thrall DE (2000) Results of irradiation of infiltrative lipoma in 13 dogs. Vet Radiol Ultrasound 41: 554-556.
McLaughlin R, Kuzma AB (1991) Intestinal strangulation caused by intra-abdominal lipoma in a dog. J Am Vet Med Assoc 199: 1610-1.
Miles J, Clarke D (2001) Intrathoracic lipoma in a Labrador retriever. J Small Anim Pract 42: 26-28.
Morini M, Bettini G, Diana A, Spadai A, Casadio Tozzi A, et al. (2009) Thymofibrolipoma in two dogs. J Comp Pathos 141 ((1)) 74-7.
Ramirez GA, Spattini G, Altimira J, Garcia B, Vilafranca M (2008) Clinical and histopathological features of a thymolipoma in a dog. J Vet Diagn Invest 20 ((3)) 360-4.
Randall C, Fox T, Fox LE (1998) Tumors of the skin and subcutis. In: Wallace B M editor. Cancer in Dogs and Cats, medical and surgical management. Philadelphia: Lippincott Williams and Wilkins. pp. 489-510.
Szabo D, Ryan T, Scott HW (2011) Carpal canal lipoma causing lameness in a dog. Vet Comp Orthop Traumatol 4: 299-302.
Thomson MJ, Withrow SJ, Dernell WS, Powers BE (1999) Intermuscular lipomas of the thigh region in dogs: 11 cases. J Am Anim Hosp Assoc 35 ((2)) 165-7.
Volta A, Bonazzi M, Gnudi G, Gazzola M, Bertoni G (2006) Ultrasonographic features of canine lipoma. Veterinary Radiology and Ultrasound 47 ((6)) 589-591.