Mitotically active leiomyoma of the uterus

by Jason Wasserman MD PhD FRCPC
September 13, 2022


What is a mitotically active leiomyoma of the uterus?

A mitotically active leiomyoma is a non-cancerous tumour that starts in the wall of the uterus. The tumour is made up of specialized smooth muscle cells that are normally found in a part of the uterus called the myometrium. Mitotically active means that dividing tumour cells called mitotic figures were seen within the tumour.

Mitotically active leiomyomas are more common in younger women, pregnant women, and in women previously treated with certain medications such as tamoxifen and progesterone. Despite the increased mitotic activity, these tumours are still non-cancerous.

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What are the symptoms of a mitotically active leiomyoma in the uterus?

Small mitotically active leiomyomas typically do not cause any symptoms. Larger tumours can cause symptoms such as abdominal pain, pressure, and vaginal bleeding.

What is the difference between a mitotically active leiomyoma and a fibroid?

In the uterus, there is no difference between a mitotically active leiomyoma and a fibroid. Both terms are used to describe the same type of non-cancerous tumour.

How is the diagnosis of mitotically active leiomyoma in the uterus made?

Mitotically active leiomyomas are often diagnosed after all or a part of the uterus has been removed and tissue has been examined under the microscope by a pathologist. For many patients, the uterus is removed for other reasons and the leiomyoma is found incidentally.

What does a mitotically active leiomyoma look like under the microscope?

When examined under the microscope, a mitotically active leiomyoma is made up of long thin cells called spindle cells. These cells are often described as growing in fascicles which are long interconnecting chains of cells. Thick-walled blood vessels and open spaces called cysts are commonly seen. The number of mitotic figures (dividing tumour cells) ranges from 2 – 6 mitotic figures per mm2 or 6 – 14 mitotic figures per 10 high-powered fields (HPF).

What does it mean if a mitotically active leiomyoma shows degenerative changes?

Degenerative change is a term pathologists use to describe the breakdown of tissue over time. It is very common to see degenerative changes in a mitotically active leiomyoma, especially larger ones that have been growing for a long time.

What does it mean if a mitotically active leiomyoma shows infarct-like necrosis?

Some mitotically active 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. Infarct-like necrosis is very common in leiomyomas that have been treated with hormone therapy or embolization.

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