Uterus: Definition

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The uterus, also called the womb, is a hollow, muscular organ in the female pelvis. It has an upside-down pear shape. It sits between the urinary bladder in front and the rectum behind. A pregnancy grows inside the uterus. A pathologist examines tissue from the uterus after a biopsy or a hysterectomy, which is surgery to remove it.

This article explains the parts and layers of the uterus, the conditions that can affect it, and what the wording on your report means.

What is the uterus?

The uterus is the organ where a pregnancy develops. A fallopian tube joins it on each side near the top. The lower end, called the cervix, connects it to the vagina. The uterus wall can change size so the organ can expand and contract. The lining also changes through the menstrual cycle.

What are the parts of the uterus?

Doctors divide the uterus into four parts, from top to bottom:

Fundus. This is the rounded top of the uterus. It sits above the point where the fallopian tubes attach.
Body. This is the main part of the uterus. It lies below the fundus.
Isthmus. This is the narrow section between the body and the cervix.
Cervix. This is the lowest part. Its opening connects the uterus to the vagina. See the cervix article.

The fallopian tubes and ovaries sit next to the uterus. See ovaries and fallopian tubes.

What are the layers of the uterine wall?

The uterine wall has three layers. From the inside out, they are:

Endometrium. This is the inner lining. It contains glands, a single layer of surface cells called epithelium, and supporting tissue called stroma. It changes through the menstrual cycle.
Myometrium. This is the thick middle layer. It consists of smooth muscle. It lets the uterus change size and contract.
Perimetrium. This thin layer covers the outside of the uterus. Reports may call it the serosa.

What conditions can affect the uterus?

Many conditions can affect the uterus. Most are not cancer. The uterus and endometrium article lists them in more detail. The main groups are:

Normal changes in the endometrium. The lining looks different at different life stages. Examples include proliferative, secretory, atrophic, and inactive endometrium.
Noncancerous growths. These include leiomyomas (fibroids) and endometrial polyps. In adenomyosis, endometrial tissue grows into the muscle wall.
Inflammation. Chronic endometritis is long-term inflammation of the lining.
Precancerous changes. Atypical endometrial hyperplasia and endometrioid intraepithelial neoplasia are changes in the lining that can lead to cancer.
Uncertain potential. A smooth muscle tumor of uncertain malignant potential is a growth in the muscle wall. Pathologists cannot say for sure how it will behave.
Cancers. The main cancers of the lining are endometrioid, serous, and clear cell carcinoma. Other cancers include carcinosarcoma, leiomyosarcoma, and endometrial stromal sarcoma.
Other conditions. These include endometriosis and products of conception, which are tissue from a pregnancy.

How do pathologists examine the uterus?

The pathologist examines tissue under the microscope. The tissue comes from one of three types of specimens:

Biopsy. A biopsy removes a small sample of the lining.
Curettage. Curettage removes tissue from the lining with a small instrument.
Hysterectomy. This operation removes the whole uterus. The pathologist can then examine all of its layers.

A small sample shows only part of the lining. For this reason, a normal result from a small sample lowers the concern but cannot rule out every condition.

What might my report say about the uterus?

Reports describe each part of the uterus separately. Each laboratory phrases it a little differently:

Endometrium. The report names the lining pattern, such as proliferative, secretory, or atrophic. It also names any polyp, hyperplasia, inflammation, or tumor.
Myometrium. The report describes the muscle wall. It also names any fibroid or adenomyosis.
Serosa. The report describes the outer surface.
Unremarkable. The pathologist saw nothing abnormal in that part.
A tumor. If the pathologist finds a tumor, the report describes which layers it involves.

Questions to ask your doctor

Which part of my uterus did the doctor sample?
What does my report say about the endometrium and the myometrium?
Did the pathologist find any growth or abnormal change?
Is the finding noncancerous, precancerous, or cancer?
Does my report mention hyperplasia or atypia?
Were the cervix, fallopian tubes, and ovaries also examined?
How do the findings explain my symptoms?
Do I need more tests, follow-up, or treatment?