Intramuscular Lipoma

What is an intramuscular lipoma?

An intramuscular lipoma is a rare, noncancerous (benign) tumor. It’s made of yellow fatty tissue that forms inside a muscle. Healthcare providers sometimes call this type of soft tissue tumor a deep-seated lipoma because it forms under the fascia. Fascia is a thin sheet of connective tissue that holds muscles in place.

What does “intramuscular lipoma” mean?

You may better understand this condition when you break down the terms:

• Intramuscular refers to the fact that the tumor develops inside a muscle in the musculoskeletal system.
• Lipomas are lumps of fatty tissue (tumors) that form under your skin. They’re the most common type of benign soft tissue tumors. Intramuscular lipomas form deeper inside a muscle, but are still made of fatty tissue. There are also intermuscular lipomas that form between muscles.

How common are intramuscular lipomas?

Intramuscular lipomas are rare, accounting for less than 1% of lipomas. Adults ages 40 to 70 are most likely to develop intramuscular lipomas. But the tumors can affect all ages and genders.

Where do intramuscular lipomas form?

Up to 15% of people have intramuscular lipomas in more than one muscle, but most people have one tumor in one muscle.

Intramuscular lipomas most commonly form deep within muscles in your:

• Arms.
• Chest wall.
• Head or neck.
• Shoulders.
• Thighs.
• Tongue.
• Trunk (pelvic area).

What are the types of intramuscular lipomas?

Certain tumor characteristics determine the type of intramuscular lipoma:

• Infiltrating intramuscular lipomas have muscle fibers growing through them. The tumors may expand into nearby tendons or fascia. Approximately 8 in 10 intramuscular lipomas are the infiltrating type.
• Well-defined (well-circumscribed) intramuscular lipomas have a clear origin within a particular muscle and distinct borders. These tumors don’t have infiltrating muscle fibers.
• Mixed intramuscular lipomas have infiltrating muscle fibers, as well as well-defined borders.

What causes intramuscular lipomas?

Experts aren’t sure why some people develop intramuscular lipomas. Potential causes include:

• Chronic irritation.
• Developmental disorders.
• Endocrine system disorders.
• Genetic disorders (gene mutations).
• Metabolic syndrome.
• Obesity.
• Traumatic accidents or injuries.

What are the symptoms of an intramuscular lipoma?

Intramuscular lipomas are slow-growing tumors. They may be smaller than half an inch (1 centimeter) or as large as 10 inches (25 centimeters). Smaller tumors don’t always cause symptoms. When symptoms occur, you may notice swelling (edema) or a soft lump underneath your skin that moves. The lump may feel firm when you contract your muscles. You may also experience muscle cramps or muscle pain.

Who diagnoses and treats intramuscular lipomas?

A medical doctor called an orthopedist diagnoses and treats conditions that affect the musculoskeletal system.

How is an intramuscular lipoma diagnosed?

Your healthcare provider relies on imaging scans to diagnose soft tissue tumors. You may get one or more of these tests:

• X-ray.
• Ultrasound.
• CT scan.
• MRI.
• Positron emission tomography (PET) scan.

You may also get a needle biopsy to confirm that the tumor isn’t a soft tissue cancer like liposarcoma.

How are intramuscular lipomas treated?

You might not need treatment if the intramuscular lipoma doesn’t cause problems. Your healthcare provider may monitor the tumor for signs of growth or changes.

Your provider may recommend treatment if the tumor causes problems or the biopsy doesn’t clearly determine whether the tumor is benign or cancerous. You may also want treatment if the lump is noticeable, making you self-conscious about your appearance.

Treatment involves surgically removing (excising) the tumor. Infiltrating tumors have a 50% to 80% recurrence rate after surgical removal. Well-defined tumors rarely grow back.

What are the complications of an intramuscular lipoma?

An infiltrating intramuscular lipoma can invade nearby tissues, tendons and muscle. A large tumor may cause a pinched nerve and neuropathy (nerve pain).

Can you prevent an intramuscular lipoma?

Intramuscular lipomas are rare and occur for unknown reasons. There isn’t any way to prevent them.

What is the outlook for someone with an intramuscular lipoma?

Most people with intramuscular lipomas don’t need treatment. If the tumor causes pain or other problems, you can have surgery to remove it.

When should I call the doctor?

Call your healthcare provider if you experience:

• Lump underneath your skin.
• Unexplained muscle pain or cramps.

What should I ask my provider?

You may want to ask your healthcare provider:

• What caused the intramuscular lipoma?
• Do I need treatment?
• Should I look for signs of complications?

Can an intramuscular lipoma become cancerous?

No. There’s no evidence of an intramuscular lipoma ever being anything but benign (not cancerous). A biopsy can help determine whether the tumor is cancerous and confirm a lipoma diagnosis.

A note from Cleveland Clinic

You should contact your healthcare provider anytime you notice changes like a lump or swelling underneath your skin. Often, these lumps are nothing to worry about. Soft tissue tumors like intramuscular lipomas are very rare. And if you have one, it’s reassuring to know that these fatty tumors aren’t cancerous. Most people don’t need treatment. But if the tumor causes pain, cramps or looks unsightly, you can get surgery to remove it.