LIPOMAS

BACKGROUND

Lipomas are benign deposits of fatty tissue. These are very common in dogs and, in one study, accounted for 35% of all tumors diagnosed in Golden Retrievers. There are three different presentations of lipomas: regular, intermuscular, and infiltrative. Regular lipomas are most commonly diagnosed in subcutaneous tissues, but intra-abdominal, intra-thoracic, pericardial, and spinal lipomas are other reported sites. Intermuscular lipomas typically occur in the caudal thigh between the semitendinosus and semimembranosus muscles, but they have also been reported in the thoracic limb (particularly the axilla). Surgical extirpation of regular and intermuscular lipomas is usually curative. Finally, infiltrative lipomas, while benign,are locally aggressive with infiltration of normal muscle and fibrous tissue (such as fascia, nerves, myocardium, joint capsule, and bone). Common locations for infiltrative lipomas include the mandible and thoracic and abdominal walls. 

DIAGNOSIS

Fine-needle aspirate cytology is sufficient for the diagnosis of a lipoma, but there are no cellular characteristics which allow differentiation of regular, intermuscular, and infiltrative lipomas. An incisional biopsy may be indicated if there is a high index of suspicion for an infiltrative lipoma. A recent study (2016) also showed that regular lipomas, infiltrative lipomas, and malignant liposarcomas have specific CT characteristics and CT may also be recommended if the clinical presentation is not consistent with a regular or infiltrative lipoma.

TREATMENT

The majority of regular lipomas do not require treatment. The principal indication for surgery is large lipomas interfering with function and/or locomotion. Surgical extirpation is recommended for intermuscular lipomas. Liposuction and intralesional triamcinolone injections have also been described with variable success rates. 

Infiltrative lipomas have a more aggressive local behaviour and require more aggressive surgical approaches to minimize the risk of local tumor recurrence. The surgical approach depends on the location of the infiltrative lipoma, but can include mandibulectomy, chest wall resection, abdominal wall resection, or limb amputation. The combination of a less aggressive surgery and radiation therapy has also been reported.

PROGNOSIS

Regular and Intermuscular Lipomas

The prognosis is excellent for dogs with regular and intermuscular lipomas is excellent. Seromas are common following removal of intermuscular lipomas and hence a drain is recommended postoperatively in most cases. However, local recurrence is very rare for both regular and intermuscular lipomas following surgical excision.

Liposuction was successful in removing 96% of 76 lipomas. The success rate was higher for simple, encapsulated lipomas < 15cm. However, complications such as bruising, hematoma formation, and seroma formation were common, and local recurrence was reported in 28% of lipomas.

A single, ultrasound-guided intralesional injection of triamcinolone resulted in complete regression of 60% of 15 lipomas and partial regression in the remaining 40% of lipomas. However, this treatment was reserved for small lipomas < 3cm in diameter and followup was limited to only 6 months post-injection.

Infiltrative Lipomas

The prognosis is guarded for dogs with infiltrative lipomas, especially if not treated aggressively. In one old paper, local tumor recurrence was reported in 36% of dogs with 67% of dogs being disease-free at 1 year after surgery. 

Last updated on 6th March 2017