Your pathology report for angiolipoma

by Bibianna Purgina, MD FRCPC
December 10, 2025

An angiolipoma is a benign (noncancerous) soft tissue tumour that develops in the subcutis, the layer of fat just beneath the skin. It is composed of two main components: mature fat cells, which resemble normal body fat, and small, thin-walled blood vessels, some of which contain tiny clots called fibrin thrombi. These features help pathologists distinguish angiolipoma from other types of fatty tumours.

Most angiolipomas are small and occur as multiple tender nodules, although some people develop only a single tumour. Because angiolipomas are benign, they do not spread to other parts of the body, and surgical removal is typically curative.

Where in the body do angiolipomas occur?

Angiolipomas most commonly occur on the arms, especially the forearms, but they can also appear on the trunk, including the chest or abdomen. They are found just beneath the skin and are not the same as haemangiomas or angiolipoma-like tumours found in deeper tissues or organs, which contain larger blood vessels and behave differently.

A variant called cellular angiolipoma contains a higher proportion of blood vessels yet remains benign.

What are the symptoms of angiolipoma?

Angiolipomas usually present as small, soft nodules beneath the skin. Unlike ordinary lipomas, which are generally painless, angiolipomas are often tender or painful, especially when touched or pressed. The reason for the pain is not fully understood, and there is no clear relationship between the number of blood vessels in the tumour and how painful it is.

Because angiolipomas are usually small and superficial, many patients notice multiple nodules in the same region.

Who gets angiolipomas?

Angiolipomas are relatively common. They usually appear in late adolescence or early adulthood, often between the late teens and early 30s. They are more common in men.

About 5% of cases occur in families, suggesting a genetic component. When inherited, angiolipomas follow an autosomal dominant pattern, meaning a person only needs to inherit one altered copy of the gene to be affected.

What causes angiolipoma?

The exact cause is unknown. In most cases, angiolipomas arise sporadically without an apparent trigger. Most tumours have a normal chromosomal pattern, although rare examples show rearrangements involving chromosome 13. Up to 80% have been reported to harbor PRKD2 mutations, although the significance of this mutation remains under study. These findings do not affect treatment and are not used in routine diagnosis.

How is this diagnosis made?

Clinical examination and imaging

Because angiolipomas occur just beneath the skin and are usually small, doctors can often diagnose them based on the physical examination alone. Imaging, such as ultrasound, may be used when the tumour is unusually deep, painful, or atypical in appearance.

Biopsy or surgical removal

The diagnosis is confirmed after a biopsy or complete removal of the tumour. A pathologist examines the tissue under the microscope to identify the characteristic features of angiolipoma.

Microscopic features

Under the microscope, angiolipomas consist of mature adipocytes, which resemble normal fat cells, mixed with numerous small, branching blood vessels. Some of these vessels contain fibrin thrombi, tiny protein clots that are a hallmark feature of this tumour. The amount of vascular tissue varies from case to case. In a cellular angiolipoma, the vascular component is more prominent, and in rare cases, the tumour may be almost entirely vascular. These features help distinguish angiolipoma from tumours that may look similar but are malignant, such as angiosarcoma or Kaposi sarcoma.

Immunohistochemistry and molecular testing

Additional laboratory testing, such as immunohistochemistry or molecular studies, is not usually necessary to diagnose angiolipoma because the microscopic features are typically clear. When performed, the results are used only to rule out other, more aggressive tumours.

Tumour size

Angiolipomas are typically small, measuring 2–3 centimetres. Size does not influence behaviour because these tumours are benign.

Margins

A margin is the edge of tissue removed during surgery. Margins are examined only when the tumour is completely excised. A negative margin means no tumour cells were found at the edge of the tissue, while a positive margin means tumour cells extend to the cut edge.

Even when margins are positive, angiolipomas very rarely recur, and additional treatment is usually not required unless symptoms persist.

What happens after the diagnosis?

Angiolipomas are always benign and, once removed, rarely recur. Because many patients have multiple tumours, new angiolipomas may develop over time, but these represent new growths rather than recurrences of old tumours. Follow-up is usually minimal unless symptoms return or new nodules develop.

If the tumour was painful, most patients experience immediate relief after removal.

Questions to ask your doctor

• Was the tumour completely removed?

• Is this a typical angiolipoma or a cellular angiolipoma?

• Do I need follow-up after surgery?

• Could I develop more angiolipomas in the future?

• Is genetic testing recommended for my family or me?