Mucinous Cystadenoma of the Ovary: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
May 25, 2026

A mucinous cystadenoma is a common, noncancerous (benign) type of ovarian tumor. It is made up of one or more fluid-filled spaces called cysts, lined by cells that produce a thick, gelatinous, mucus-like fluid called mucin. Although a mucinous cystadenoma is not cancer and does not spread to other parts of the body, it can grow very large. In fact, mucinous tumors are among the largest tumors in the body, and for this reason, a mucinous cystadenoma can sometimes cause noticeable symptoms. It is usually found in only one ovary, and it is one of the most common benign tumors of the ovary.

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 mucinous cystadenoma?

The cause of a mucinous cystadenoma is not known. It is not caused by an infection and is not contagious. There are no clearly established lifestyle causes, and in most cases there is no identifiable reason why a particular person develops this type of tumor. Mucinous cystadenomas can occur at any age but are most often found in adult women, including during the reproductive years and around the time of menopause.

What are the symptoms?

Many mucinous cystadenomas cause no symptoms, particularly when they are small, and are discovered during an imaging test or examination performed for another reason. Because these tumors can grow very large, symptoms, when they occur, are usually related to the presence of a large mass and may include:

Abdominal swelling or bloating — An increase in abdominal size or a feeling of fullness or distension. Because mucinous cystadenomas can become very large, this is a common reason for seeking medical attention.
Abdominal or pelvic pain — Discomfort or pain in the lower abdomen or pelvis.
Pressure symptoms — A large cyst can press on nearby organs, sometimes causing changes in urination or bowel habits.

Because these symptoms are common and can have many causes, they are not specific to a mucinous cystadenoma. Any persistent abdominal or pelvic symptom should be evaluated by a doctor.

How is the diagnosis made?

For most women, the diagnosis of a mucinous cystadenoma is made after the tumor is surgically removed and sent to a pathologist for examination under the microscope. Depending on the situation, the fallopian tube on the same side, and sometimes the uterus, may be removed at the same time. Imaging tests such as ultrasound, CT, or MRI may show a cyst in the ovary, but they cannot confirm the diagnosis on their own.

During the operation, the surgeon may request an intraoperative consultation (also called a frozen section). In this situation, the pathologist examines a sample of the tumor while the patient is still in the operating room and provides a preliminary diagnosis within minutes. The result of an intraoperative consultation can change the type of surgery performed. A final diagnosis is made later, once the entire tumor has been examined in detail.

Because mucinous tumors can be very large and can contain different areas with different appearances, the pathologist examines and samples the tumor thoroughly. This careful sampling is important to confirm that the entire tumor is benign and that there are no areas that would change the diagnosis to a mucinous borderline tumor or a mucinous carcinoma.

What does a mucinous cystadenoma look like under the microscope?

Most mucinous cystadenomas look and feel like a balloon filled with fluid. The inside of the tumor may be a single large space or, more often, many smaller spaces, all filled with fluid. Pathologists call these spaces cysts. When the tumor is examined under the microscope, several features are characteristic:

Mucinous lining cells — The inside of the cysts is lined by a single, flat layer of cells that produces mucin, the thick gelatinous fluid that fills the tumor. The cells resemble those that normally line parts of the digestive tract, and may be described as gastrointestinal-type or intestinal-type.
A simple, orderly lining — In a mucinous cystadenoma, the lining cells form a thin, even layer without significant crowding or complex growth. This simple appearance is what separates a benign mucinous cystadenoma from a mucinous borderline tumor.
Adenofibroma pattern — Some tumors have thicker walls or solid areas that contain more supporting tissue and fewer cysts. These may be called a mucinous adenofibroma or mucinous cystadenofibroma. They are still completely benign.

While examining the tumor, the pathologist also looks for two findings that are sometimes seen in small amounts within an otherwise benign mucinous cystadenoma:

Focal atypia — Atypia is a word pathologists use to describe cells that look different from the cells normally found in a location. Most mucinous cystadenomas contain no atypical cells. When small areas of atypical cells are present, the tumor may be described as a mucinous tumor with focal atypia.
Focal epithelial proliferation — Some tumors contain small areas where the lining cells form more complex growths rather than a simple flat layer. When this is limited to small areas, the tumor may be described as a mucinous tumor with focal epithelial proliferation.

When atypia or epithelial proliferation is limited to small focal areas, the tumor is still considered benign. If these areas are more extensive, the diagnosis may instead be a mucinous borderline tumor. This is another reason the pathologist thoroughly samples mucinous tumors.

What happens after this diagnosis?

A mucinous cystadenoma is benign. It is not cancer, and it does not spread to other parts of the body. Once the tumor has been completely removed, it is considered cured.

The discussion between you and your gynecologic team about treatment and follow-up depends on the size of the cyst, whether it is causing symptoms, your age, and your overall situation. Points the team may discuss include:

Surgical removal — Most mucinous cystadenomas are removed surgically, particularly when they are large or causing symptoms. The surgery may involve removing only the cyst, or removing the affected ovary and fallopian tube, depending on the situation.
Complete removal — Because a large mucinous tumor can contain different areas, removing the tumor intact and in full allows the pathologist to confirm that the entire tumor is benign.
The possibility of a new cyst — When only the cyst is removed and the ovary is left in place, a new cyst can occasionally develop later. This is not a return of cancer, because a mucinous cystadenoma is not cancer.
No need for chemotherapy or radiation — Because a mucinous cystadenoma is benign, treatments used for cancer, such as chemotherapy and radiation therapy, are not needed.

Most people who have a mucinous cystadenoma removed need no further treatment. Your doctor will let you know whether any follow-up is recommended based on your individual situation.

Questions to ask your doctor

Was the tumor confined to one ovary, or were both ovaries involved?
Was the entire cyst removed, or was only part of it removed?
Was the diagnosis confirmed as a benign mucinous cystadenoma, with no borderline or cancerous areas?
Were any areas of atypia or epithelial proliferation found?
Do I need any further treatment?
Is there a chance another cyst could develop in the future?
Do I need any follow-up imaging or appointments?
What symptoms should prompt me to contact you?