Leiomyoma of the uterus

by Jason Wasserman MD PhD FRCPC
June 7, 2022

About this article: This article was created by doctors to help you read and understand your pathology report for leiomyoma of the uterus. If you have any questions about this article or your pathology report, please contact us.

What is a leiomyoma of the uterus?

A leiomyoma is a non-cancerous tumour that starts in the wall of the uterus. The tumour is made out of a specialized type of tissue called smooth muscle. Leiomyomas are very common tumours and they usually occur in women between 20 and 50 years old. Leiomyomas can start anywhere in the myometrium. Those that grow near the serosa are called subserosal. Those that grow near the endometrium are called submucosal. Another name for leiomyoma is a fibroid.

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What are the symptoms of a leiomyoma in the uterus?

These tumours can bulge into the inner cavity of the uterus where they can cause bleeding or even interfere with pregnancy. Although they are benign, leiomyomas can grow to be very large which can cause pain and pressure on surrounding organs such as the bladder.

How is the diagnosis of leiomyoma in the uterus made?

Leiomyomas are often diagnosed after the uterus has been removed, often for other conditions such as cancer of the cervix, endometrium, or ovaries. In this situation, if a leiomyoma is identified in the uterus, the report will simply include leiomyoma in the diagnosis section without providing additional information about the leiomyoma.

If the uterus is removed for the purpose of removing a leiomyoma (or multiple leiomyomas), the diagnosis may include additional information although the amount and type of information provided vary between pathologists and hospitals.

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Tumour infarct or degeneration

Some leiomyomas grow so large that blood cannot get to all of the cells in the tumour. The cells that do not receive blood undergo a type of cell death called necrosis and the area of the tumour that dies is described as an infarct. Infarcts are very common in leiomyomas that have been treated with hormone therapy or embolization.

In other cases, the cells do not die but the tumour shows signs of ageing that pathologists describe as degeneration. Some reports may use words like hydropic or hyaline to describe the degenerative changes seen in the tumour. Both infarcts and degeneration are common in leiomyomas and are not associated with a worse prognosis.

Mitotic activity

Cells divide in order to create new cells. This process is called mitosis and a cell that is dividing is called a mitotic figure. Dividing cells are seen in some leiomyomas and if present, the number of mitotic figures may be included in your report.


The tumour cells in a leiomyoma usually look very similar to normal smooth muscle cells. However, when examined under the microscope, some tumour cells may look different. Atypical tumour cells are larger and darker than normal muscle cells. Atypical cells are often seen in very large leiomyomas. Although they look abnormal, atypical tumour cells are not cancer cells and are not associated with a worse prognosis.

Cellular leiomyomas

A cellular leiomyoma is a tumour that has more cells than the average leiomyoma. Despite the increased number of cells, the tumour is still non-cancerous.

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