Angiomyolipoma (AML)

by Jason Wasserman MD PhD FRCPC
July 22, 2024


Background:

Angiomyolipoma (AML) is a benign (non-cancerous) tumour made up of a combination of adipose tissue (fat), smooth muscle, and blood vessels. This type of tumour is most commonly found in the kidney, although it can also be found in the liver and pancreas.

What causes angiomyolipoma?

Most angiomyolipomas contain a genetic alteration that renders the gene TSC2 (or less commonly TSC1) inactive. Both TSC2 and TSC1 are tumour suppressor genes which means they prevent cells from growing and dividing uncontrollably. For most people who develop an angiolipoma, the condition is sporadic, which means the loss of TSC2 or TSC1 is not associated with any pre-existing genetic condition. What causes the loss of TSC2 or TSC1 in these people is still unknown. Angiomyolipomas, however, are much more common in people with tuberous sclerosis, a genetic syndrome caused by the loss of TSC2 or TSC1.

What are the symptoms of angiomyolipoma?

Most angiomyolipomas do not cause any symptoms, and the tumour is discovered incidentally (by accident) when imaging of the abdomen or pelvis is performed for another reason.

What is the difference between a PEComa and an angiomyolipoma?

PEComa is a type of tumour made up of specialized perivascular epithelioid cells that make proteins normally found in melanocytes (HMB45, melan-A, and MITF) and smooth muscle cells (SMA and calponin). Because angiomyolipoma is believed to start from perivascular cells and because it typically produces these proteins, it is considered a type of PEComa.

How is this diagnosis made?

The diagnosis can be made after part or all of the tumours are removed, and the tissue is sent to a pathologist for examination under the microscope.

Microscopic features of this tumour

When examined under the microscope, angiomyolipoma comprises a combination of mature adipocytes (fat cells), variably sized blood vessels, and smooth muscle cells. Pathologists often perform a test called immunohistochemistry to confirm the diagnosis. When this test is performed the tumour cells are typically positive for the melanocytic markers HMB45, melan-A, and MITF and the smooth muscle markers SMA and calponin. The tumour cells are typically negative for epithelial cell markers such as pan-cytokeratin.

This pictures shows an angiomyolipoma examined under the microscope.
This picture shows an angiomyolipoma examined under the microscope.

About this article

Doctors wrote this article to help you read and understand your pathology report. If you have additional questions, contact us.

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