An angiolipoma is a noncancerous tumor that develops in the layer of fat just beneath the skin. It has two parts: mature fat cells that look like normal body fat and many small, thin-walled blood vessels.
Angiolipomas are common and are closely related to ordinary lipomas. What sets them apart for most people is that they are often tender or painful, while a lipoma usually is not. They do not spread to other parts of the body, and removing one is curative.
This article explains how an angiolipoma is diagnosed and what the findings in your pathology report mean.
Angiolipomas usually appear in late adolescence or early adulthood, most often between the late teens and the early thirties. They are more common in men.
Many people develop several angiolipomas, often in the same area, and new ones may appear over a period of years. About 5% of cases run in families, in a pattern where only one copy of an altered gene needs to be passed on.
Angiolipomas develop just beneath the skin. The most common location is the forearm, and they also occur on the upper arm and the trunk. They are rarely found elsewhere, such as inside the mouth or near the spine.
A variant called cellular angiolipoma contains more blood vessels and less fat. It behaves the same way and is also noncancerous.
An angiolipoma usually appears as a small, soft lump beneath the skin, most often less than 2 cm across. Many people have more than one.
Unlike most lipomas, angiolipomas are frequently tender, and pressing on the lump can be uncomfortable. The reason for the pain is not well understood. It does not match the number of blood vessels in the tumor, so a painful angiolipoma is not more worrisome than a painless one.
Several other noncancerous lumps under the skin can also be painful, so tenderness alone does not confirm the diagnosis.
The cause of an angiolipoma is not known, and most occur without any apparent trigger. Injury, diet, and weight do not cause them.
Studies have found genetic changes in the tumor cells themselves. About 80% of angiolipomas carry a change in a gene called PRKD2, and a similar proportion carry a change in PIK3CA. Both genes are involved in blood vessel growth, which may explain the vessel-rich appearance of this tumor.
These changes are found only in the tumor and are not inherited. They are not tested for in routine practice and do not affect treatment.
Because angiolipomas sit just beneath the skin and are usually small, a doctor can often recognize one during a physical examination. Doctors may use imaging such as ultrasound when the lump is unusually deep, large, or painful. The diagnosis is confirmed after the lump is removed and examined by a pathologist.
Under the microscope, an angiolipoma is made of mature fat cells mixed with many small, branching blood vessels. The vessels are most numerous at the edge of the tumor. A thin capsule usually surrounds the whole lump.
Many of the small vessels contain tiny clots made of a protein called fibrin. Your report may describe these as fibrin thrombi, and they are the most useful clue for this diagnosis. The cells lining the vessels look normal, and there are no features of a cancerous tumor.
Extra tests are usually not needed. When the vessels are especially prominent, as in a cellular angiolipoma, a pathologist may use immunohistochemistry to rule out vascular cancers such as angiosarcoma and Kaposi sarcoma. A stain for human herpesvirus 8 is negative in angiolipoma and positive in Kaposi sarcoma.
Angiolipomas are typically small, usually 2 cm or less and rarely larger than 3 cm. Size does not change how this tumor behaves, because an angiolipoma is noncancerous whatever its size. Size is recorded in the report mainly as a description of what was removed.
A margin is the edge of tissue cut by the surgeon. Margins are examined only after the surgeon has removed the whole lump.
A negative margin means no tumor cells were seen at the cut edge, and a positive margin means tumor cells reach it. For an angiolipoma, a positive margin is not a cause for concern in the way it is for cancer. These tumors rarely come back even when a margin is positive, and further surgery is usually not needed unless symptoms continue.
The outlook after angiolipoma removal is excellent. These tumors are noncancerous, do not spread, and do not turn into cancer. Recurrence at the same site is rare.
Many people develop new angiolipomas elsewhere over time. These are new growths rather than a return of the removed tumor, and they do not mean anything was missed.
Treatment depends on whether the lump causes symptoms.
People with many angiolipomas sometimes have several removed over time, usually the ones causing the most discomfort.