Discovering an unexpected lump beneath your beloved pet's skin can be quite unsettling, prompting a prompt visit to the veterinarian for a thorough evaluation. Fortunately, more often than not, the diagnosis is reassuringly simple: "just a lipoma" or colloquially, a "fatty tumor." But what exactly is a lipoma, and why should pet owners be familiar with it?
Meet the Lipocyte (Also Known as the Adipocyte)
Fat is a valuable resource in our bodies. It serves various functions, from providing energy during steady activity to insulation against the cold. Our bodies are remarkably efficient at storing fat, a characteristic that has unfortunately contributed to the ongoing battle against obesity. Fat is stored within cells known as lipocytes, commonly referred to as fat cells. These cells consist of a thin outer membrane and a nucleus surrounding a spacious fat storage area known as a vacuole. A normal fat cell can expand significantly as it accumulates fat.
The Mystery of the Lipoma
Tumors can develop in any type of tissue, including fat tissue. It's not uncommon for benign tumors called lipomas to form within fat cells. These tumorous fat cells grow at a different rate than the surrounding fat tissue, resulting in the formation of a lump. Depending on the amount of fat a lipoma stores, it can grow quite large. If a cat is already overweight, lipomas become even more noticeable and larger. As overweight cats shed those extra pounds, their lipomas may shrink, although complete disappearance is unlikely. The good news is that lipomas are benign, meaning they don't invade other tissues or spread destructively. While lipomas are primarily seen in dogs, especially older overweight dogs, cats can occasionally develop them as well.
How Do We Identify a Lipoma?
Lipomas typically have a distinctive texture—they feel rubbery and relatively soft. However, diagnosing a lump based solely on how it feels may not be entirely accurate. A simple and common procedure to confirm a lipoma is a needle aspirate, where a small sample of cells is withdrawn from the mass using a syringe and examined for the presence of fat droplets on a microscope slide. This procedure often yields reliable results. Of course, in cases where there's any doubt, a tissue biopsy can provide a definitive diagnosis.
To Remove or Not to Remove the Lipoma?
In most cases, the presence of a lipoma is primarily a cosmetic concern. If the lump is unsightly or in an uncomfortable or mobility-impairing location, it can usually be safely removed, provided the patient is in good health for anesthesia. Sometimes, lipomas are left alone if they don't seem to bother the cat. Surgical removal is usually straightforward, as most lipomas can be gently peeled away from their location.
The Elusive Malignant Lipoma
There's a less common and more troublesome version of the lipoma that infiltrates nearby tissues and is challenging to remove. This type of lipoma lacks a distinct capsule and clear boundaries. It has a 36% recurrence rate, whereas typical lipomas usually don't grow back.
Though rare, there exists a malignant form of the lipoma called a liposarcoma. This tumor is also invasive but typically doesn't spread aggressively throughout the body like traditional malignancies. To control this type of fat tumor, extensive surgical excision is necessary.
Surprisingly, all three types of lipomas (the regular, the infiltrative, and the malignant) appear identical when aspirated for fat cells during an office examination.
Lookalikes and Their Deceptions
There are a couple of malignant tumors that can mimic the rubbery texture of a lipoma. For example, the mast cell tumor is a highly inflammatory and potentially very malignant growth of the skin and subcutaneous tissue. The appearance of cells from a mast cell tumor differs from that of a lipoma, allowing for distinction during the initial office evaluation. Another imitator is the hemangiopericytoma, which also feels rubbery like a lipoma and contains enough fat to complicate aspiration examination. In fact, some soft tissue sarcomas may be challenging to distinguish from a lipoma, but they generally feel more deeply rooted and firm. Biopsy may be required to obtain a conclusive diagnosis when a rubbery mass doesn't fit the typical lipoma profile.
If you notice a lump or growth on your cat, it's advisable to consult your veterinarian. Most lumps require some form of tissue sampling for diagnosis, although there are a few that can be identified through visual inspection by your veterinarian. Since any lump has the potential to be a significant growth, it's crucial to take lumps and growths seriously and have your cat thoroughly examined by a qualified veterinarian. Your furry friend's well-being is always worth the extra attention!
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