Hibernoma

What is a hibernoma?

A hibernoma is a rare, noncancerous (benign) soft tissue tumor made of brown fat. Most people only have one hibernoma, although it’s possible to have more. These tumors grow slowly and don’t spread to other parts of your body.

What does the term “hibernoma” mean?

You may better understand this condition when you break down what it means:

• “Hiber” refers to the tumor’s brown color. Also called brown adipose tissue, the fatty substance resembles the brown fat that hibernating bears make. It works in a similar way too, warming your body when you’re cold.
• “-oma” is the medical term for a tumor regardless of whether it’s cancerous (malignant).

What is the difference between a hibernoma and lipoma?

A hibernoma and lipoma are both benign soft tissue tumors. These tumors occur for no known reason.

• Lipomas are the most common type of benign soft tissue tumor. These fatty lumps of tissue are white in color.
• Hibernomas are a rare type of benign soft tissue tumor. These fatty lumps of tissue have a brown color.

How common are hibernomas?

Hibernomas are rare, accounting for less than 1% of benign soft tissue tumors. People between 20 and 40 years of age are most likely to develop hibernomas. But children and older people get them too.

Where do hibernomas form?

Hibernomas most commonly appear underneath the skin on your thighs. You may also find this fatty lump of tissue on your:

• Arms.
• Back.
• Chest or breasts.
• Neck.
• Scalp.
• Scrotum (part of the male reproductive system).
• Shoulders.
• Vulva (part of the female reproductive system).

Approximately 1 in 10 hibernomas form within muscles, soft tissues or ligaments in your musculoskeletal system. They may develop in your:

• Larynx (voice box).
• Lungs.
• Pelvis (trunk area).
• Space behind your abdominal cavity (retroperitoneum).

What are the types of hibernomas?

Different cells can form different types of hibernomas. A biopsy of the tumor determines the type. Hibernoma types include:

• Typical lobular hibernoma: Approximately 8 out of 10 hibernomas are this type. These tumors mostly appear on your thighs, trunk or chest. They can also form within muscles.
• Lipoma-like hibernoma: This tumor typically appears on your thighs. It tends to be mostly white in color with brown specks, resembling a lipoma.
• Myxoid hibernoma: This type most commonly forms on the scalp or shoulders of people assigned male at birth.
• Spindle-cell hibernoma: Only about 2% of hibernomas are the spindle-cell type. They tend to form on your scalp or the back of your neck.

What causes hibernomas?

Experts believe that changes within certain chromosomes (gene mutations) cause some people to develop hibernomas. Benign soft tissue tumors are also more common in people who have multiple endocrine neoplasia (MEN) syndromes. These often-inherited conditions cause tumors to form in glands in your endocrine system.

What are the symptoms of a hibernoma?

Hibernomas rarely cause pain. You may notice a lump underneath your skin that feels:

• Movable.
• Round.
• Rubbery or soft.
• Warm.

Who diagnoses and treats hibernomas?

You may receive medical care from an orthopedist. This medical doctor specializes in diagnosing and treating conditions that affect the musculoskeletal system.

How is a hibernoma diagnosed?

Healthcare providers use imaging scans to diagnose soft tissue tumors. You may get one or more of these tests:

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

You may also get a needle biopsy to confirm a hibernoma diagnosis. A biopsy can also help rule out a rare soft tissue cancer like liposarcoma. During the biopsy, your healthcare provider uses a thin needle to take a sample of tissue from the tumor. A lab analyzes the tissue sample for diseased cells.

What do hibernomas look like?

Hibernomas typically measure between 2 inches and 4 inches (5 centimeters to 10 centimeters). Hibernomas that form within the abdominal cavity can grow as large as 8 inches (20 centimeters). The fat color may vary from a light tan to reddish-brown. You won’t be able to see the coloring, but your healthcare provider will see it when they surgically remove the tumor.

How are hibernomas treated?

Depending on the location of the tumor on your body, surgeons from different can remove (excise) hibernomas. Your doctor may recommend surgery even if the tumor isn’t causing symptoms. Surgically removing the tumor is the best way to confirm the hibernoma diagnosis and ensure the tumor isn’t cancerous.

What are the complications of a hibernoma?

In rare instances, a hibernoma can grow too large and invade nearby tissues, nerves and organs. A tumor can press against nerves, leading to neuropathy. Depending on the location of the tumor, this nerve pain may appear as:

• Carpal tunnel syndrome.
• Knee pain.
• Lower back pain or sciatica.
• Thoracic outlet syndrome.

Can you prevent a hibernoma?

Hibernomas are rare. There isn’t any way to prevent the gene change that causes them.

What is the outlook for someone with a hibernoma?

Surgery to remove a hibernoma cures the condition. The tumor is unlikely to come back after surgical treatment.

When should I call the doctor?

Call your healthcare provider if you experience:

• Chronic cough (which may indicate a tumor on or near the lungs).
• Lump underneath your skin.
• Unexplained pain in your back, hands, knees or other parts of your body.

What should I ask my provider?

You may want to ask your healthcare provider:

• What caused the hibernoma?
• What is the best treatment?
• Should I look for signs of complications?

Can a hibernoma become cancerous?

No. It’s rare for a benign soft tissue tumor to become cancerous. There’s no evidence of a hibernoma ever being anything but benign (not cancer). However, it’s not possible to tell the difference between a hibernoma and a soft tissue cancer without a biopsy. For this reason, providers often recommend removing the tumor.

A note from Cleveland Clinic

It can be disconcerting to find an unexpected lump beneath your skin or to hear that you have a tumor. Fortunately, soft tissue tumors like hibernomas are very rare — and they’re not cancerous. Many people are surprised to find out they have one. Your healthcare provider will discuss treatment options with you. Most people get surgery to remove the tumor and confirm that it’s a hibernoma and not a cancerous tumor.