Corpus Luteum Cyst of the Ovary: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 31, 2026

A corpus luteum cyst is a noncancerous (benign) fluid-filled space in the ovary. It develops from the corpus luteum, a normal structure that forms in the ovary every month after an egg is released. The corpus luteum makes progesterone, the hormone that prepares the lining of the uterus for a possible pregnancy. Its name comes from the Latin for “yellow body” because the cells fill with fat as they make hormones, turning the structure yellow.

When the corpus luteum does not break down on schedule, or when blood or fluid collects inside it, it enlarges into a cyst. Because the cyst arises from the normal working of the ovary, it is called a functional cyst. Corpus luteum cysts are very common in women of reproductive age and are especially often seen in early pregnancy.

A corpus luteum cyst is not a tumor, and it is not cancer. It does not turn into cancer over time. 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 corpus luteum cyst?

Every month, a follicle in the ovary grows and then opens to release an egg. The emptied follicle does not disappear. Its cells change, fill with fat, and reorganize into the corpus luteum, which begins making progesterone. This is a normal part of every menstrual cycle.

What happens next depends on whether a pregnancy occurs. If there is no pregnancy, the corpus luteum shrinks about 10 to 14 days after ovulation and leaves behind a small scar called the corpus albicans. If there is a pregnancy, the corpus luteum keeps working for longer.

A corpus luteum cyst forms when this normal process does not follow its usual course. There are two common reasons. The corpus luteum may fail to shrink at the end of the cycle and instead keep growing and filling with fluid. Or a small blood vessel may bleed into the center of the corpus luteum around the time of ovulation, filling it with blood. A cyst formed this way is called a hemorrhagic corpus luteum cyst.

This is a normal variation in how the ovary works, not a disease.

What are the symptoms?

Many corpus luteum cysts cause no symptoms and are found incidentally on an imaging test. When symptoms occur, they are usually one-sided and related to cyst size or bleeding.

Pelvic pain or pressure — A dull ache low on one side of the abdomen, often in the second half of the menstrual cycle.
A late or irregular period — A corpus luteum cyst can keep producing progesterone, which may delay a period or cause irregular bleeding.
Sudden, sharp pain — The cyst can burst, which is called rupture. This causes sudden one-sided pain and can cause bleeding into the abdomen. Rupture is more likely to cause significant bleeding in people taking blood-thinning medication.
Sudden, severe pain with nausea — A large cyst can cause the ovary to twist on its blood supply, a problem called torsion. This is an emergency and requires prompt surgery.

Sudden severe pelvic pain has several possible causes, some of which need urgent treatment. It should always be assessed promptly rather than waited out.

What does a corpus luteum cyst mean if I am pregnant?

A corpus luteum cyst is a normal finding in early pregnancy. After conception, the corpus luteum does not shrink. It keeps producing progesterone to support the pregnancy until the placenta takes over, which usually happens between 8 and 12 weeks. During that time, it often becomes cystic, and it is commonly seen on the first pregnancy ultrasound.

A corpus luteum cyst does not harm the pregnancy. In almost all cases,s it shrinks on its own during the second trimester and needs no treatment. The corpus luteum is doing useful work early in pregnancy. Surgeons therefore avoid removing it in the first trimester unless there is a clear reason, such as rupture or torsion. If it must be removed very early, your team may give progesterone to replace what the corpus luteum was providing.

A corpus luteum cyst can also form when you are not pregnant. Finding one on an ultrasound or a pathology report says nothing about whether you are pregnant, only that you ovulated during that cycle.

How is the diagnosis made?

Most corpus luteum cysts are identified on an imaging test rather than by a pathologist. On ultrasound, the cyst has a thick, slightly wavy wall with a rim of blood flow around it, and it often contains a lacy pattern from clotted blood inside. This appearance is characteristic enough that radiologists usually recognize it, and the usual next step is a repeat ultrasound several weeks later to confirm that the cyst has gone.

A corpus luteum cyst appears on a pathology report in one of two situations. The first is as an incidental finding, when the ovary was removed for another reason, and the pathologist noticed the cyst while examining the tissue. The second is when the cyst ruptured, caused significant pain, or looked unusual on imaging, and was removed surgically for that reason. Emergency surgery for bleeding into the abdomen is one route by which these cysts reach the laboratory.

When the tissue arrives, the pathologist records the cyst’s size and appearance, then examines the lining under the microscope. Recognizing the luteinized lining cells is what confirms the diagnosis.

What does a corpus luteum cyst look like under the microscope?

A corpus luteum cyst is a fluid-filled or blood-filled space lined by the hormone-producing cells of the corpus luteum. To the naked eye, the wall is often bright yellow or yellow-orange, and the cavity commonly contains blood or a blood clot. Under the microscope, the pathologist looks for the following features.

Luteinized granulosa cells — The inner lining is made of large cells with abundant pink, slightly bubbly cytoplasm. The word luteinized describes cells that have filled with fat to make hormones.
An outer layer of luteinized theca cells — Smaller cells sit just outside the granulosa cell layer. Both layers come from the follicle that released the egg.
A wavy, scalloped border — The lining folds in and out rather than forming a smooth circle. This convoluted outline is one of the most useful clues that the cyst is a corpus luteum cyst.
A thin fibrous inner layer — A layer of scar-like tissue often lines the innermost surface, reflecting healing after ovulation.
Blood and pigment — Red blood cells, blood clot, and brown pigment left behind by older bleeding are all common. These findings are expected and not a sign of cancer.
Bland nuclei — The lining cells can look enlarged or irregular in places as they age and break down. These changes are degenerative rather than a sign of a tumor.

What other findings may be described in the report?

Along with a corpus luteum cyst, your pathology report may describe several other features of the ovary and the tissue around it.

Cyst size — The report gives the greatest dimension in centimeters. Pathologists generally use the term corpus luteum cyst for a corpus luteum larger than 3 cm, so size is what decides whether the word cyst is used at all.
Intact or ruptured — The report may note whether the cyst was whole when removed or had already burst. Rupture of a functional cyst carries none of the significance it would for a tumor.
Hemorrhage — The report may describe blood inside the cyst or in the surrounding tissue. This is common and expected.
Other normal structures — The report may mention cystic follicles, a corpus albicans, or primordial follicles. All are normal parts of an ovary at different points in the cycle.
Other findings in the same ovary — Anything else present, such as endometriosis or a separate tumor, is reported separately.

How is this different from other ovarian cysts?

The ovary can produce several kinds of cysts, and the pathologist tells them apart by what lines the inside. Your report may mention one of the following.

Follicle cyst — Forms because an egg was not released, rather than after one was. A follicle cyst is also a functional cyst and also noncancerous. Its lining cells are usually not luteinized, and its wall is smooth rather than scalloped.
Endometriotic cyst — Lined by tissue like that of the lining of the uterus and filled with old blood. This is a feature of endometriosis and is managed differently. Because both can be full of blood, imaging can sometimes confuse the two.
Serous cystadenoma — A benign tumor rather than a functional cyst, lined by cells resembling those of the fallopian tube. A serous cystadenoma does not resolve on its own.
Cystic granulosa cell tumor — A low-grade cancer that can form a cyst. It is usually much larger, and the lining cells are disorganized and grow into the wall. Telling this apart from a functional cyst is one reason the pathologist examines the lining carefully.

What happens after this diagnosis?

A corpus luteum cyst is a normal, noncancerous finding in the ovary. It does not require treatment in its own right, and it does not turn into cancer. If the cyst was found incidentally in tissue removed for another reason, your care will be guided by that other diagnosis rather than by the cyst. Points your doctor may raise include:

No follow-up for the cyst itself — Once a cyst has been removed and confirmed as a functional cyst, no further monitoring is needed for it.
New cysts can form — A new corpus luteum forms after every ovulation. If you still have ovaries and are still ovulating, you may develop additional functional cysts. This is normal and is not a recurrence.
Hormonal contraception — Birth control that prevents ovulation reduces how often new functional cysts form, because no corpus luteum is created in a cycle without ovulation.
Fertility — Functional cysts do not damage fertility. If one ovary was removed, the other usually continues to work normally.
Recovery after bleeding — If the cyst ruptured and caused bleeding into the abdomen, your recovery is guided by that event rather than by the cyst itself.

Sudden severe pelvic pain, especially with nausea, vomiting, dizziness, or fainting, should be assessed urgently, since rupture with bleeding and torsion both need prompt treatment.

Questions to ask your doctor

Was the cyst found by chance, or was it the reason for my surgery?
How large was the cyst?
Was the cyst intact, or had it ruptured?
Was there bleeding into my abdomen, and how was it managed?
Was any part of the ovary removed, or only the cyst?
Was there any concern that this could be a tumor rather than a functional cyst?
If I am pregnant, does this cyst affect my pregnancy?
If the corpus luteum was removed early in pregnancy, do I need progesterone support?
Were any other findings described in the ovary or fallopian tube?
Am I likely to develop cysts like this again?
Could this affect my periods or my fertility?
Do I need any follow-up imaging or appointments?
What symptoms should prompt me to contact you?