Myelolipoma

by Jason Wasserman MD PhD FRCPC
March 2, 2022


What is a myelolipoma?

Myelolipoma is a non-cancerous tumour that is typically found in the adrenal gland. Although non-cancerous, the tumour can grow to be very large which can cause symptoms associated with compression of nearby organs. Myelolipoma is the second most common type of adrenal gland tumour. There is no known cause for most patients who develop a myelolipoma.

How do pathologists make this diagnosis?

The diagnosis of myelolipoma can be made after a small sample of tissue is removed in a procedure called a biopsy or after the entire tumour is removed. The tissue is then sent to a pathologist for examination.

What does a myelolipoma look like under the microscope?

When examined under the microscope, myelolipoma is made up of two types of cells: adipocytes (fat cells) and cells normally found in the bone marrow. The relative proportion of these two types of cells varies between tumours.  Pathologists use the term mature adipocytes to describe the normal-appearing fat cells typically found throughout the tumour. The bone marrow cells normally found in a myelolipoma include megakaryocytes and immature white blood cells. Pathologists use the term trilineage hematopoiesis to describe this combination of normal bone marrow elements. A rim of the normal adrenal gland may be seen surrounding or adjacent to the tumour.

Because large tumours may bleed, your pathology report may describe the presence of hemorrhage, red blood cells, or hemosiderin within the tumour. Large open spaces called cysts may also be seen, especially in large tumours.

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