Cellular Leiomyoma of the Uterus: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
September 2, 2026

A cellular leiomyoma is a noncancerous (benign) tumor that develops in the muscular wall of the uterus, which is called the myometrium. Leiomyomas are made of smooth muscle cells, the same cells that make up the normal wall of the uterus. In the uterus, leiomyoma and fibroid mean the same thing, so a cellular leiomyoma is a type of fibroid.

cellular leiomyoma uterus

The word “cellular” describes what the pathologist sees. In an ordinary fibroid, the muscle cells are spread apart in abundant collagen. In a cellular leiomyoma, the cells are packed more tightly together, with less collagen between them. That difference in density is the only thing separating the two diagnoses.

A cellular leiomyoma is not cancer, and it does not spread to other parts of the body. Doctors treat it like any other fibroid. This article will help you understand what this diagnosis means on your pathology report, what each term means, and why it matters for your care.

What causes a cellular leiomyoma?

The cause of fibroids is not fully understood. Each one grows from a single smooth muscle cell that begins dividing more than it should, and its growth depends on estrogen and progesterone. That is why fibroids appear during the reproductive years and often shrink after menopause.

Several factors increase the risk of fibroids, including a family history, starting periods at an early age, and excess body weight. Fibroids are more common and tend to appear earlier in Black women than in other groups. Nothing is known to make the cellular type specifically more likely; the increased cell density is a variation in appearance rather than a different disease.

An infection does not cause fibroids, they are not contagious, and nothing you did caused this one.

What are the symptoms?

A cellular leiomyoma causes the same symptoms as any other fibroid, and small ones usually cause none. Many are found by chance when the uterus is examined for another reason. Symptoms depend on the size of the tumor and where it sits in the wall of the uterus.

Heavy or prolonged periods — The most common symptom, particularly when the fibroid bulges into the cavity of the uterus.
Pelvic pressure or fullness — Caused by the bulk of a larger fibroid.
Pelvic or abdominal pain — Sometimes constant, sometimes worse around a period.
Pressure on nearby organs — A large fibroid can press on the bladder or bowel, changing how often you need to urinate or how your bowels work.
Difficulty becoming pregnant — Fibroids that distort the cavity of the uterus can interfere with pregnancy.

How is the diagnosis made?

Fibroids are usually seen first on an ultrasound or MRI, but no imaging test can tell a cellular leiomyoma from any other fibroid. The distinction is made only under the microscope, after the tumor has been removed.

The tissue reaches the laboratory after a myomectomy, in which the fibroid is removed alone, or after a hysterectomy. In many cases, the uterus was removed for another reason, and the fibroid was an incidental finding.

A pathologist then examines the tumor, comparing its cell density with the surrounding muscle wall and assessing how the cells look. When the tumor is densely cellular, pathologists sometimes perform additional stains, as described below.

What does a cellular leiomyoma look like under the microscope?

A cellular leiomyoma is a benign smooth muscle tumor of the uterus in which the cells are packed more tightly together than usual. Under the microscope, the pathologist looks for the following features.

Densely packed spindle cells — The tumor is made of long, thin cells called spindle cells, arranged in interlacing bundles called fascicles. In a cellular leiomyoma, these cells sit closer together than in an ordinary fibroid, and closer together than in the surrounding wall of the uterus.
Less collagen — There is still supporting tissue between the cells, simply less of it than in an ordinary fibroid.
Normal-looking cells — The cells are uniform, without the marked variation in size and shape that pathologists call nuclear atypia.
Few dividing cells — A cell caught in the act of dividing is called a mitotic figure. These are infrequent in a cellular leiomyoma.
Thick-walled blood vessels — A characteristic feature of fibroids, and a useful clue that a densely cellular tumor is a fibroid rather than something else.
Cystic spaces — Open, fluid-filled spaces described as cysts are common, particularly in larger tumors.

A small number of these tumors are described as highly cellular leiomyomas. The cells are packed even more tightly, and the tumor edge may extend irregularly into the surrounding wall. This appearance can resemble another type of tumor, which is why stains are used in these cases.

Immunohistochemistry

Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside cells. Most cellular leiomyomas need no additional testing. Stains are used when the tumor is densely cellular. A densely cellular fibroid can look similar to a tumor arising from the lining tissue of the uterus rather than from muscle. Those tumors are called endometrial stromal tumors, and some of them are cancers, so the distinction matters.

Desmin. Usually positive. Desmin is a structural protein found in muscle cells, so a positive result supports a smooth muscle tumor such as a fibroid.
h-caldesmon. Usually positive. This protein is the most reliable muscle marker here because endometrial stromal tumors are typically negative for it.
CD10. Usually negative or only patchy. CD10 is characteristic of the lining tissue of the uterus. It is not a perfect separator, since some fibroids stain for it as well, which is why it is interpreted alongside the other two.

No single stain settles this question, and pathologists use the three together with the appearance of the tumor. If your report lists these stains, they were performed to confirm that the tumor came from muscle.

What do degenerative changes and infarct-like necrosis mean?

As fibroids grow and age, parts of the tumor may begin to break down. Pathologists call this degenerative change. It is very common in cellular leiomyomas, especially in larger tumors that have been present for a long time, and it does not mean the tumor is cancerous.

Some fibroids grow so large that blood cannot reach the entire tumor. Cells that lose their blood supply die, a process called necrosis. When the pattern of cell death resembles an infarct, meaning an area of tissue killed by loss of blood supply, it is called infarct-like necrosis. This is also common after treatment with hormone medication or after uterine artery embolization, a procedure that deliberately blocks blood flow to shrink a fibroid.

The word necrosis also appears in the criteria used to diagnose cancer, so seeing it in a benign report is understandably confusing. The two are not the same. Infarct-like necrosis follows loss of blood supply and shows a zone of healing tissue between the dead and living areas. Tumor cell necrosis, the kind that counts toward a diagnosis of cancer, has an abrupt border with no healing zone. Distinguishing between them is a routine part of the pathologist’s assessment.

How is this different from a leiomyosarcoma?

A uterine leiomyosarcoma is a cancer made of the same kind of smooth muscle cells. Pathologists separate it from a benign fibroid using three features together.

Cell division — How many tumor cells are dividing.
Nuclear atypia — Whether the cells look abnormal.
Tumor cell necrosis — Whether tumor cells are dying in the pattern seen in cancer.

Cell density is not one of them. A cellular leiomyoma has more cells than usual and none of these three features, which is why it is benign. If your report says cellular leiomyoma, the pathologist assessed all three and did not find them.

How does this differ from other types of leiomyoma?

Fibroids come in several forms that differ in appearance under the microscope. Your report may use any of the following terms, and the first four are all benign.

Leiomyoma — The usual form. Spindle cells in bundles, spread apart in collagen.
Cellular leiomyoma — The cells are packed more tightly together.
Mitotically active leiomyoma — An increased number of dividing cells, with normal-looking cells and no tumor cell necrosis. A mitotically active leiomyoma is benign.
Leiomyoma with bizarre nuclei — Also called atypical or symplastic leiomyoma. The cells look strikingly abnormal, but dividing cells are few, and there is no tumor cell necrosis. These behave benignly in almost all cases.
Smooth muscle tumor of uncertain malignant potential — A tumor with a combination of features fitting neither a benign fibroid nor a leiomyosarcoma. A STUMP is not cancer, but its behavior is less predictable, and it is followed more closely.

What other findings may be described in the report?

Your report will describe the tumor and the rest of the uterus. Findings commonly listed include:

Tumor size and number — Fibroids are often multiple, and each is measured. Size does not change the fact that the tumor is benign.
Location in the wall — Whether the fibroid sits within the wall, bulges into the cavity, or projects from the outer surface. This is what best explains the symptoms.
The lining of the uterus — If a hysterectomy was performed, the endometrium is examined and reported separately. The report may also note an endometrial polyp or endometrial hyperplasia alongside the fibroid.
Adenomyosis — Endometrial-type tissue within the muscular wall, a common accompanying finding that causes similar symptoms.
Margins — If only the fibroid were removed, the report may note whether it appeared completely excised.

What happens after this diagnosis?

A cellular leiomyoma is a benign fibroid and is managed like any other fibroid. It is not given a grade,e and it is not assigned a stage, because grading and staging describe cancers. Points your doctor may raise include:

No cancer treatment — Chemotherapy and radiation are not used for this tumor.
No special follow-up — The increased cell density does not call for extra monitoring. Follow-up is the same as for an ordinary fibroid.
If the fibroid alone was removed — New fibroids can develop in the remaining uterus over time, and existing ones can grow. This is not a recurrence of anything worrying.
If the whole uterus was removed — Fibroids cannot come back.
Fertility — Removing a fibroid that was distorting the cavity of the uterus can improve the chance of pregnancy. Your surgeon can explain what your operation means for future pregnancies.
After menopause — Fibroids usually shrink once hormone levels fall. A fibroid that grows after menopause should be assessed.

Most people need no further treatment. Your doctor will tell you whether any follow-up is recommended in your situation.

Questions to ask your doctor

Was this tumor confirmed as benign?
Was the fibroid completely removed?
Did you consider a leiomyosarcoma or another tumor, and what ruled it out?
Were any special stains performed, and what did they show?
My report mentions necrosis. Is that the benign kind?
Did the tumor cells show any abnormal features under the microscope?
How large was the fibroid, and was there more than one?
Where in the wall of the uterus was it?
Could this explain the bleeding or pressure I was having?
Could new fibroids develop, and would I need surgery again?
Does this affect my fertility or a future pregnancy?
What treatment options exist if I develop new symptoms?
Do I need any follow-up imaging or appointments?