Cortical Inclusion Cyst of the Ovary: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 31, 2026

A cortical inclusion cyst is a small, noncancerous (benign) space in the outer part of the ovary. Pathologists use the word cyst for any closed space in a tissue, however small. The cortex is the ovary’s outer layer, where these cysts sit. They form when a small piece of the tissue covering the surface of the ovary becomes trapped just below the surface.

Cortical inclusion cysts are extremely common. Most are only a few millimeters across, and by convention they measure less than 1 cm. They are found in the ovaries of most adult women when the tissue is examined under the microscope, and their number increases with age. Your report may also call them epithelial inclusion cysts, germinal inclusion cysts, or Müllerian inclusion cysts.

A cortical inclusion cyst is not a tumor or cancer. It causes no symptoms, needs no treatment, and requires no follow-up. This article will help you understand what this term means on your pathology report and why it appears there at all.

What causes a cortical inclusion cyst?

Cortical inclusion cysts result from ovulation. Each month, when an egg is released, the ovary’s surface breaks open and then heals over. During healing, a small piece of surface tissue can fold inward and become sealed beneath the surface. Cut off from the outside, it forms a tiny closed space.

This can happen in two ways, and pathologists can sometimes tell them apart. In the first, the trapped tissue comes from the ovary’s own covering. In the second, a small piece of lining from the nearby fallopian tube settles on the open surface of the ovary at ovulation and becomes sealed in. This second type is lined by tube-like cells and is more common in adults.

Because these cysts depend on ovulation, they are not seen before puberty, and they accumulate slowly over the reproductive years. This is a normal consequence of ovaries doing their usual work. It is not a disease, an infection does not cause it, and it is not inherited.

What are the symptoms?

Cortical inclusion cysts cause no symptoms. They are far too small to feel, and in almost all cases too small to see on an ultrasound, CT, or MRI. They do not grow into a mass, do not press on anything, and are never the reason for surgery.

This matters if you had pain, bleeding, or another symptom before your surgery. A cortical inclusion cyst does not explain those symptoms. If your report lists this finding, look for the other diagnoses in the report, and ask your doctor which one accounts for what you were experiencing.

How is the diagnosis made?

A cortical inclusion cyst is only ever identified by a pathologist looking at ovarian tissue under the microscope. You can’t diagnose it on an imaging test, in the operating room, or by examining the specimen with the naked eye. It is always an incidental finding, meaning it is noticed while the tissue is being examined for another reason.

The ovary reaches the laboratory for many reasons: removal of a separate ovarian tumor, a hysterectomy, surgery for endometriosis, treatment of another cancer, or risk-reducing surgery. In every one of those situations, the pathologist examines the whole ovary and describes everything present. Cortical inclusion cysts are among the most commonly described findings.

Pathologists mention them because a complete report describes what they see, not only what is abnormal. Their presence in your report shows thoroughness rather than that something is wrong.

What does a cortical inclusion cyst look like under the microscope?

A cortical inclusion cyst is a small round space in the outer part of the ovary, lined by a single layer of cells. Under the microscope, the pathologist looks for the following features.

A single layer of lining cells — The space is lined by one thin layer of epithelium, the type of tissue that covers surfaces in the body. There is no crowding and no piling up of cells.
Flat or tube-like cells — The lining cells are either flat and inconspicuous, or taller cells with fine hair-like projections called cilia. Cilia are normally found in the lining of the fallopian tube, and their presence here is expected rather than abnormal.
Small size — These cysts are usually a fraction of a millimeter to a few millimeters across, and by definition under 1 cm.
A position in the cortex — They sit in the outer part of the ovary, often close to the surface, and are frequently multiple.
Occasional calcium deposits — Small rounded deposits of calcium, called psammoma bodies, are sometimes present in the tissue nearby. This type of calcification is common and harmless.
No abnormal cells — The lining cells look ordinary. Crowding, complex growth, or abnormal-looking cells would point to a different diagnosis.

What is the difference between a cortical inclusion cyst and a serous cystadenoma?

Size, and nothing else. A cortical inclusion cyst and a serous cystadenoma can be lined by the same kind of cells and look identical under the microscope. Pathologists use a 1 cm cutoff to decide which term applies.

Under 1 cm — Reported as a cortical inclusion cyst. Treated as a normal, incidental finding.
Over 1 cm — Reported as a serous cystadenoma or a serous cystadenofibroma. These are benign tumors, and they are usually large enough to be seen on imaging.

As with the 3 cm cutoff used for follicle cysts, the 1 cm figure is a convention agreed on by pathologists rather than a point at which the biology changes. Both diagnoses are noncancerous.

Are cortical inclusion cysts linked to ovarian cancer?

If you search for this term, you will find research papers asking whether some ovarian tumors begin in cortical inclusion cysts. That research is worth understanding because, on its face, it sounds alarming, but it is not.

Scientists studying where ovarian cancer starts have found that most high-grade serous carcinoma, the most common ovarian cancer, begins in the fallopian tube rather than the ovary. A minority of cases cannot be traced to the tube, and one hypothesis is that those begin in a cortical inclusion cyst lined by tube-like cells. This remains a question under investigation, not a fact.

What this means for you is straightforward. Cortical inclusion cysts are present in most adult ovaries, and ovarian cancer is uncommon. Having them found in your ovary does not raise your risk, and they are not considered a precancerous change. No pathologist grades them, no doctor monitors them, and no treatment exists or is needed. They are a normal feature of an ovary that has been ovulating for years.

What other findings may be described in the report?

A cortical inclusion cyst is rarely the only finding in a report. Your report will also describe the rest of the ovary and any other tissue removed, and one of those other findings is usually the reason for the surgery. Findings commonly listed alongside cortical inclusion cysts include:

Other normal structures — Primordial follicles, cystic follicles, a corpus luteum, or a corpus albicans. All are normal parts of an ovary at different points in the menstrual cycle.
Functional cysts — A follicle cyst or a corpus luteum cyst. Both are noncancerous.
Surface adhesions — Scar tissue on the outside of the ovary, usually from previous surgery, infection, or endometriosis.
A separate tumor — If a tumor was the reason for surgery, it is described separately and in detail. That diagnosis, not the inclusion cysts, guides your care.
The fallopian tube — When the tube is removed with the ovary, it is examined and reported separately.

What happens after this diagnosis?

Nothing needs to happen because of a cortical inclusion cyst. It is a normal finding; it requires no treatment and no follow-up imaging or appointments. Your care after surgery is determined entirely by the other findings in your report.

If cortical inclusion cysts are the only abnormality named in your report, that is a reassuring result. It means the pathologist examined the ovary and found nothing of concern. If other diagnoses are listed, discuss those with your doctor.

Questions to ask your doctor

Was a cortical inclusion cyst the only finding in my ovary?
If not, which finding was the reason for my surgery?
Which finding explains my symptoms?
Does this finding require any treatment or follow-up?
Does having these cysts change my risk of ovarian cancer?
Was a serous cystadenoma or any other ovarian tumor found?
Was the fallopian tube examined, and what did it show?
Was anything found in the other ovary?
Do I need any further imaging or appointments?
What symptoms should prompt me to contact you?