Intramuscular myxoma

by Jason Wasserman MD PhD FRCPC
March 30, 2023

What is an intramuscular myxoma?

An intramuscular myxoma is a non-cancerous tumour made up of spindle cells surrounded by myxoid tissue and located within a muscle.

Is an intramuscular myxoma benign or malignant?

An intramuscular myxoma is a benign (non-cancerous) type of tumour.

Can an intramuscular myxoma turn into cancer over time?

No. Intramuscular myxoma will not turn into cancer over time.

Where are intramuscular myxomas commonly found in the body?

The most common locations for an intramuscular myxoma are the large muscles of the thigh, shoulder, buttock, and upper arm.

What causes an intramuscular myxoma?

For most people who develop an intramuscular myxoma, the cause is unknown. However, these tumours are more common in people with Mazabraud syndrome, a genetic condition that also leads to bone abnormalities called fibrous dysplasia.

What are the symptoms of an intramuscular myxoma?

Most intramuscular myxomas present as a painless, slow-growing mass.

At what age do most intramuscular myxomas occur?

Most intramuscular myxomas occur in people between the age of 40 and 70 years old and women are three times more likely to develop this tumour compared to men.

How is an intramuscular myxoma diagnosed?

The diagnosis is usually made through a combination of medical imaging (CT scan or MRI) and examination of tissue under the microscope by a pathologist.

What does an intramuscular myxoma look like under the microscope?

When examined under the microscope, an intramuscular myxoma is made up of long thin spindle cells surrounded by myxoid tissue which appears light blue when stained with hematoxylin and eosin (H&E). Tumours with very few cells are called hypocellular while those with lots of cells are called cellular or hypercellular. A type of tissue breakdown described as degenerative change is often also seen. The areas of degenerative change may include hemorrhage (blood), fibrosis (scarring), and cysts (small holes in the tissue). Clumps of calcium called calcifications may also be seen.

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