Ovarian Fibroma: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 29, 2026

An ovarian fibroma is a noncancerous (benign) tumor of the ovary. It grows from fibroblasts, the cells that make the firm supporting tissue found inside the ovary. Because it is made almost entirely of this supporting tissue, an ovarian fibroma is solid and firm rather than fluid-filled. It belongs to a family of tumors called sex cord-stromal tumors, and it is the most common benign tumor in that group.

Ovarian fibromas account for roughly 4 percent of all ovarian tumors. They most often occur in middle age and around the time of menopause, and they are uncommon before age 30. Size varies widely, from under 1 cm to more than 20 cm. Almost all involve one ovary only.

An ovarian fibroma is not cancer, and it does not spread to other parts of the body. 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 an ovarian fibroma?

The cause of an ovarian fibroma is not known. It is not caused by an infection, it is not contagious, and no lifestyle factor has been shown to cause it. In most cases, there is no identifiable reason why one person develops this tumor.

A small number of ovarian fibromas occur as part of an inherited condition called nevoid basal cell carcinoma syndrome, also known as Gorlin syndrome. This syndrome is caused by a change in a gene called PTCH1, which normally helps limit how much cells grow. When that brake is lost, tumors can form in several organs, including the skin, the jaw, and the ovaries.

Fibromas linked to this syndrome look different from ordinary ones. They tend to occur in younger patients, involve both ovaries, form multiple separate nodules, and contain calcium deposits. When a pathologist sees that combination, the report may suggest considering testing for the syndrome. Most ovarian fibromas are not related to Gorlin syndrome, and a single fibroma in one ovary in an adult is not a reason to suspect it.

What are the symptoms?

Most ovarian fibromas cause no symptoms. Small tumors are usually found by chance, either during an imaging test performed for another reason or when an ovary is removed for another reason. When symptoms do occur, they usually come from the size of the tumor.

Abdominal or pelvic pain — Discomfort or pressure low in the abdomen or pelvis.
Abdominal swelling — A large tumor can make the abdomen feel full or look enlarged.
Sudden, severe pain — A large ovarian tumor can twist on its blood supply, a problem called torsion. This causes sudden severe pain and needs urgent medical attention.
Fluid in the abdomen — Some ovarian fibromas, particularly large ones, cause fluid to collect in the abdomen. This is called ascites.

A small number of people with an ovarian fibroma develop fluid in both the abdomen and the chest. The combination of an ovarian fibroma, ascites, and fluid around the lung is called Meigs syndrome. It occurs in roughly 1 percent of ovarian fibromas. Meigs syndrome closely resembles advanced ovarian cancer, and the blood test CA-125 can be raised as well. Many people in this situation are investigated for cancer before the diagnosis is known. The fluid clears on its own once the tumor is removed.

How is the diagnosis made?

An ovarian fibroma is diagnosed after the tumor is removed surgically and examined under the microscope by a pathologist. The surgery usually removes the whole ovary, sometimes along with the fallopian tube on the same side. In many cases, the fibroma was not the reason for the operation and is found unexpectedly.

Imaging tests such as ultrasound, CT, or MRI show a firm, solid mass in the ovary. Because the tumor is made of dense fibrous tissue, it has a characteristic appearance on MRI. Even so, imaging cannot reliably separate an ovarian fibroma from other solid ovarian tumors, including cancers. A solid ovarian mass on a scan is usually reported as needing surgery to establish the diagnosis. This is why many people are told a tumor is suspicious before the benign diagnosis is confirmed.

During the operation, the surgeon may request an intraoperative consultation, also called a frozen section. The pathologist examines a piece of the tumor while the patient is still in the operating room and gives a preliminary diagnosis within minutes. That result can change how much tissue the surgeon removes. The pathologist makes the final diagnosis later, once the whole tumor has been examined in detail.

The pathologist samples the tumor in several places, paying attention to any area that looks different from the rest. This matters because the features that separate an ordinary fibroma from its more cellular relatives may be present in only part of the tumor. The same is true of the features that separate it from a rare cancer called fibrosarcoma. When the microscopic appearance fits more than one diagnosis, additional stains may be performed, as described below.

What does an ovarian fibroma look like under the microscope?

An ovarian fibroma is a benign ovarian tumor made of fibroblasts and the collagen they produce. To the naked eye, it is usually a firm, solid, white or pale tumor with a whorled cut surface. Under the microscope, the pathologist looks for the following features.

Spindle cells — The tumor is made of long, thin cells called spindle cells, named for their tapered shape. They are usually arranged in bundles, called fascicles, that cross one another.
Dense collagen — The cells sit in thick supporting tissue that the report may describe as hyalinized or fibrotic. Both words mean the tissue is firm and rich in collagen.
Bland nuclei — The cells look uniform. Marked variation in the size and shape of the nuclei, which pathologists call nuclear atypia, is not seen in an ordinary fibroma.
Few dividing cells — A cell caught in the act of dividing is called a mitotic figure. The pathologist counts these because the number helps separate a fibroma from its more cellular relatives.
Degenerative changes — Large or long-standing tumors may show bleeding into the tumor, and areas of tissue death called infarct-type necrosis. This happens when the tumor outgrows its blood supply. This type of necrosis is expected in a large fibroma and is not a sign of cancer.
Calcium deposits — Small amounts of calcium may be present. Extensive calcification, especially in a young patient with tumors in both ovaries, raises the possibility of Gorlin syndrome.

Immunohistochemistry

Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside cells. For an ovarian fibroma, these stains confirm that the spindle cells come from the supporting tissue of the ovary. They also separate this tumor from other spindle cell tumors that can look similar. If the tests were performed, your report lists the results as protein names with positive or negative beside each one.

Inhibin and calretinin. Often positive, but usually only in scattered areas. These proteins are made by the ovary’s hormone-producing and supporting cells. Patchy staining supports an ovarian fibroma. Strong staining throughout the tumor points instead toward a thecoma, a related tumor.
WT1. Usually positive. WT1 is commonly present in tumors that arise from ovarian supporting tissue.
Estrogen receptor and progesterone receptor. Often positive. The estrogen receptor and progesterone receptor are proteins that respond to female hormones. A positive result is expected and does not mean the tumor is hormone-driven or that hormone treatment is needed.
Other markers. Stains such as desmin, S100, and cytokeratin are usually negative. Negative results help rule out a muscle tumor, a nerve sheath tumor, or a tumor that spread from elsewhere.

Two further tests are sometimes used when the tumor is densely cellular. A reticulin stain outlines the fibers around individual cells, which follows a different pattern in a fibroma than in an adult granulosa cell tumor. Testing for a change in a gene called FOXL2 can also help, because that change is found in most adult granulosa cell tumors and is absent in fibromas. Not every case requires any of these tests.

What do cellular fibroma and mitotically active cellular fibroma mean?

Ovarian fibromas sit at one end of a group of related tumors that differ in how tightly packed the cells are and how often they divide. Your report may use one of the following terms. All three are noncancerous.

Fibroma — The usual form. The cells are spread out in abundant collagen, and dividing cells are rare.
Cellular fibroma — The cells are more tightly packed than usual, with less collagen between them. Dividing cells remain infrequent, at fewer than 4 per 10 high power fields, the standard microscope area pathologists use for counting. A cellular fibroma is still benign.
Mitotically active cellular fibroma — The cells are tightly packed and dividing more often, at 4 or more per 10 high power fields, but they do not look markedly abnormal. A mitotically active cellular fibroma behaves benignly in almost all cases. Because a small number have come back locally, doctors often recommend a period of follow-up.

These distinctions matter because a rare cancer called ovarian fibrosarcoma is made of similar spindle cells. Under the current World Health Organization criteria, a diagnosis of fibrosarcoma requires both frequent cell division and cells that look clearly abnormal throughout the tumor. A high number of dividing cells on its own is not enough. If your report says fibroma, cellular fibroma, or mitotically active cellular fibroma, the pathologist has looked for those features and concluded the tumor is not a cancer.

What other findings may be described in the report?

Along with the diagnosis of ovarian fibroma, your pathology report may describe other features of the tumor and the surrounding tissue.

Tumor size — The report gives the greatest dimension in centimeters. Size does not change the fact that the tumor is benign, but it does influence the type of surgery performed and how likely symptoms are.
One or both ovaries — About 90 percent of ovarian fibromas involve one ovary only. Involvement of both ovaries is uncommon and prompts a pathologist to consider Gorlin syndrome, particularly in a younger patient.
Tumor surface and adhesions — The report may note whether the surface was smooth or whether the tumor was stuck to nearby tissue. Adhesions usually result from previous inflammation or surgery.
Rupture — The report may state whether the tumor was intact or had ruptured. Rupture does not carry the significance it would for a cancer, because a benign tumor does not spread.
Other findings in the ovary — The report describes the rest of the ovary and any other tissue removed, including the fallopian tube and, when removed, the uterus.

What happens after this diagnosis?

An ovarian fibroma is a benign ovarian tumor. It does not spread to other parts of the body, and it is considered cured once it has been completely removed. Because it is not cancer, it is not given a grade, and it is not assigned a stage. Grading and staging describe how a cancer is behaving and how far it has spread, and neither applies here.

What you and your gynecologic team discuss next depends on the type of fibroma, your age, and your overall situation. Points the team may raise include:

No further cancer treatment — Chemotherapy and radiation therapy are not used for this tumor, because it is benign.
Recurrence — An ordinary ovarian fibroma does not come back once removed. For a cellular or mitotically active cellular fibroma, your team may suggest a follow-up period, since a small number of these have recurred in the same area.
Symptoms settling — If the tumor caused ascites or fluid around the lung, that fluid clears after the tumor is removed and does not require separate treatment.
Fertility — Removing one ovary does not usually prevent future pregnancy, since the other ovary continues to work. Your team can explain what your surgery means for you.
Testing for Gorlin syndrome — If the fibromas involved both ovaries, formed multiple nodules, or occurred at a young age, your doctor may discuss referral for genetic assessment. This matters for blood relatives as well as for you.

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

Questions to ask your doctor

Was the diagnosis an ordinary fibroma, a cellular fibroma, or a mitotically active cellular fibroma?
Was there any concern that the tumor could be a fibrosarcoma?
How large was the tumor?
Was the tumor in one ovary only, or were both ovaries involved?
Were multiple separate tumors found?
Should I be assessed for Gorlin syndrome, and does this affect my family?
Was the ovary removed, or only the tumor?
Was the fallopian tube removed as well?
My report mentions necrosis. Does that mean anything worrying?
Were special stains performed, and what did they show?
If I had fluid in my abdomen or chest, will it come back?
Do I need any follow-up imaging or appointments?
What symptoms should prompt me to contact you?