Felipedia

Feline lipomas

Lipomas are benign tumors of adipose tissue, perhaps more accurately characterized as hamartomas. They are common in dogs, occasionally identified in cats and horses, and rare in other domestic species. In dogs, they generally occur in older, obese females, most commonly on the trunk and proximal limbs. The breeds most at risk are Doberman Pinschers, Labrador Retrievers, Miniature Schnauzers, and mixed-breed dogs. Older, neutered male, Siamese cats are predisposed, and tumors are most commonly found on the ventral abdomen. Obesity does not appear to be a factor in the development of lipomas in cats. Affected horses are generally <2 yr old. Lipomas typically appear as soft, occasionally pedunculated, discrete nodular masses, and most are freely movable. In dogs and cats, >5% are multiple. In general, these tumors float when placed in formalin. A rare variant of this tumour, diffuse lipomatosis, has been identified in Dachshunds, in which virtually the entire skin is affected, resulting in prominent folds on the neck and truncal skin. Many lipomas merge imperceptibly with the adjacent non-neoplastic adipose tissue, making it difficult to determine when the entire lesion is excised. Lipomas with an abundant connective tissue stroma (fibrolipomas), cartilaginous stroma (chondrolipomas), or a prominent vascular component (angiolipomas) are also recognized. Despite their benign nature, lipomas should not be ignored because they tend to enlarge over time, and their gross presentation may be indistinguishable from that of infiltrative lipomas or liposarcomas (see below). Excision is curative. In dogs, dietary restriction several weeks before surgery may allow for better definition of the surgical margins of the tumour.

Infiltrative lipomas (intra- and intermuscular lipomas) are rare in dogs and even less common in cats and horses. In dogs, they are most common in middle-aged females, usually on the thorax and limbs. The breeds (dogs) most at risk are the same as those for lipomas. These tumors are poorly confined, soft, nodular to diffuse swellings that typically involve the subcutaneous fat and underlying muscle and connective tissue stroma. Infiltrative lipomas, which dissect along fascial planes and between skeletal muscle bundles, are considered sarcomas of intermediate malignancy. They rarely metastasize. Aggressive excision is recommended, and amputation may be necessary.

Liposarcomas are rare neoplasms in all domestic animals. Most are recognized in older male dogs in which they usually develop on the trunk and extremities; Shetland Sheepdogs and Beagles may be predisposed. In cats, feline leukaemia virus infection has been infrequently associated with their development; whether this is a coincidence or such infections play a causative role remains undefined. Liposarcomas are nodular and soft to firm. They may exude a mucinous fluid when sectioned. Many have palpable, partially encapsulated areas, but these zones should not be construed as evidence of a benign tumour. Liposarcomas are malignant neoplasms that have a low metastatic potential but are frequently pseudoencapsulated. Wide excision is recommended. Recurrence is common, so follow-up radiation therapy is indicated in cases with insufficient margins.