by Jason Wasserman MD PhD FRCPC
April 19, 2026
Mature teratoma of the ovary is a noncancerous (benign) ovarian tumor. It is one of the most common ovarian tumors, accounting for about 20% of all ovarian neoplasms, and it can occur at any age, though it is most often diagnosed in women of reproductive age. Mature teratoma is also known as a mature cystic teratoma or a dermoid cyst, though “dermoid cyst” is an older term that is no longer preferred. The word “mature” refers to the fact that the tumor is made up of fully developed, normal-appearing tissue — unlike an immature teratoma, which contains incompletely developed tissue and behaves like a cancer. This article will help you understand the findings in your pathology report — what each term means and why it matters for your care.
What are the symptoms?
Many people with a mature teratoma have no symptoms at all, and the tumor is found by chance during imaging or surgery performed for another reason. When symptoms do occur, they typically relate to the mass’s size and may include abdominal or pelvic pain, a feeling of pressure or fullness in the lower abdomen, or a palpable mass.
A rare but important associated condition is anti-NMDAR encephalitis — an inflammatory condition in which the immune system mistakenly attacks the brain, triggered in some cases by proteins produced by neural tissue inside the teratoma. Symptoms of anti-NMDAR encephalitis can include confusion, memory problems, seizures, unusual movements, or behavioral changes. This condition can be serious, but in most cases it improves or resolves after the teratoma is removed. If you or a family member experienced neurological symptoms before or around the time of diagnosis, let your medical team know.
What causes mature teratoma of the ovary?
The exact cause is not fully known. The most widely accepted explanation is that mature teratomas develop from a single germ cell — a specialized cell in the ovary that normally develops into an egg. Through a process that does not involve fertilization by sperm, this cell begins to divide and gives rise to a wide variety of mature tissues. This is sometimes called the parthenogenetic theory, where “parthenogenetic” refers to development arising from a single unfertilized cell. The genetic material in the tumor comes entirely from the person in whom the tumor develops, and no hereditary gene mutations are known to cause mature teratomas.
About 10% of people develop mature teratomas in both ovaries, either at the same time or at different points in life.
How is the diagnosis made?
The diagnosis is usually made after the tumor is removed at surgery and examined by a pathologist. In many cases, the tumor is first suspected on imaging — an ultrasound, CT scan, or MRI — which may show a mass in the ovary containing fat, calcifications (calcium deposits), or other tissue types. These imaging features are characteristic of mature teratomas and help distinguish them from other ovarian masses before surgery.
When the pathologist examines the removed tumor without a microscope, it typically appears as a cyst (a fluid-filled sac) measuring 5 to 10 cm, though larger tumors are not uncommon. Inside, the cyst may contain thick oily or sebaceous fluid, hair, teeth, cartilage, or bone — reflecting the diverse tissue types the tumor can produce. A solid nodule called the Rokitansky protuberance is often present on the inner wall of the cyst; this firm bump is where the most complex tissue components, including hair and teeth, are commonly found.
Under the microscope, the tumor contains mature tissues derived from the body’s three germ layers — the basic categories of tissue that form during early development. These are the ectoderm (which gives rise to skin, hair follicles, sweat glands, and nervous tissue), the mesoderm (which gives rise to fat, cartilage, bone, and muscle), and the endoderm (which gives rise to the lining of the lungs, intestines, and thyroid gland). Most mature teratomas contain tissues from at least two of these layers, most commonly skin and its appendages alongside fat or other mesenchymal tissue.
One specific subtype worth knowing about is struma ovarii — a mature teratoma in which thyroid tissue is the predominant or sole component. Struma ovarii can occasionally produce thyroid hormones and cause symptoms of hyperthyroidism.
A critical part of the pathologist’s examination is carefully searching the entire specimen for any areas of immature tissue, particularly immature neural (nerve) tissue. Even small foci of immature tissue change the diagnosis from a benign mature teratoma to a malignant immature teratoma, which requires different staging and treatment. This thorough examination is the reason pathology reports for teratomas often describe sampling of multiple tissue blocks from different areas of the tumor.
Histologic grade
Mature teratoma of the ovary is not graded. Grading systems used for ovarian carcinomas assess how abnormal the tumor cells look and how aggressively the tumor is likely to behave — information that is only meaningful for malignant tumors. Because a mature teratoma is benign by definition — composed entirely of fully developed, normal-appearing tissues — no such assessment is needed or applicable. If any immature tissue is identified, the diagnosis changes to immature teratoma, which is then graded based on the amount of immature neural tissue present.
Somatic malignant transformation
In rare cases — estimated at less than 2% of mature teratomas — a cancer can develop within the teratoma itself. This is called somatic malignant transformation, meaning that one of the mature tissues inside the teratoma undergoes cancerous change. The most common type is squamous cell carcinoma arising from the skin lining of the cyst, but other types — including adenocarcinoma, thyroid carcinoma, carcinoid tumor, and others — have been reported.
Somatic malignant transformation is more common in older patients (typically over age 45–50) and in larger tumors. When it occurs, the tumor is no longer considered benign, and treatment follows the approach for the specific cancer type identified. If your pathology report mentions any evidence of malignant transformation, your gynecologic oncologist will discuss what this means for your treatment and follow-up.
Gliomatosis peritonei
Gliomatosis peritonei is a rare finding in which small deposits of mature neural (nerve) tissue are found on the peritoneum — the thin lining of the abdominal cavity — in patients with a mature teratoma. Despite the potentially alarming appearance of tumor implants on the peritoneum, gliomatosis peritonei is not the same as cancer spread and does not usually worsen the prognosis. The deposits are made up of mature tissue, not malignant cells, and the vast majority of patients with this finding do well after removal of the primary teratoma. It will be noted in your pathology report if present.
What is the prognosis?
The prognosis for mature teratoma of the ovary is excellent. Complete surgical removal is curative in virtually all cases. Recurrence after complete removal is extremely rare. Even when small foci of unexpected immature tissue or other unusual features are found on thorough examination, outcomes remain very favorable in most cases.
The rare exception is somatic malignant transformation, which carries a prognosis that depends on the type and stage of the cancer that has developed within the teratoma. This is discussed further in the section above on somatic malignant transformation.
What happens after the diagnosis?
For most patients, no further treatment is needed after complete surgical removal of a mature teratoma. The surgical approach depends on the clinical situation: in many cases, particularly in younger patients who wish to preserve fertility, a cystectomy (removal of the cyst while leaving the ovary) is performed. In other situations, removal of the entire ovary (oophorectomy) is done. Your gynecologist will have discussed these options with you before surgery.
Because about 10% of patients develop mature teratomas in both ovaries, the surgeon typically examines the other ovary at the time of surgery. If imaging has not already assessed the other ovary, or if there was any concern at the time of surgery, your doctor may recommend follow-up imaging.
If anti-NMDAR encephalitis was diagnosed or suspected before or around surgery, close follow-up with a neurologist is important. In most cases, neurological symptoms improve significantly or resolve after the tumor is removed, but recovery can take weeks to months and ongoing neurological monitoring may be recommended.
If somatic malignant transformation was identified in the teratoma, referral to a gynecologic oncologist is required for staging and treatment planning.
For patients in whom the diagnosis was made on a cystectomy specimen (where only the cyst was removed), follow-up imaging may be recommended to confirm that any remaining ovarian tissue appears normal and that there is no recurrence over time.
Questions to ask your doctor
- Was the tumor completely removed, and was it a cystectomy (cyst only) or an oophorectomy (entire ovary)?
- Were all areas of the tumor examined, and was any immature tissue found?
- Was any evidence of somatic malignant transformation — cancer developing within the teratoma — identified?
- Was the other ovary examined, and did it appear normal?
- Is follow-up imaging recommended to monitor the remaining ovarian tissue or check for recurrence?
- Was gliomatosis peritonei noted in the report, and what does that mean for my follow-up?
- Were there any neurological symptoms before or around my diagnosis, and should I be evaluated for anti-NMDAR encephalitis?
- What is the risk of developing a teratoma in my other ovary, and should it be monitored?
- Do I need any further treatment, or is surgery alone sufficient?
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