Cysts can and do form in the uterus, though they get far less attention than their ovarian counterparts. They can develop in the cervix, within the muscular wall of the uterus, along the endometrial lining, and even from leftover embryological tissue. Most uterine cysts are benign and many produce no symptoms at all, but the range of conditions that create cyst-like spaces in or near the uterus is surprisingly broad, and a few deserve medical attention.
Nabothian Cysts Are the Most Common Type
If your doctor has ever casually mentioned a cyst on your cervix during a routine exam, it was almost certainly a nabothian cyst. These are small, mucus-filled bumps that form on the surface of the cervix when mucus-producing glands get blocked by overlying tissue. They are benign, extremely common in women of reproductive age, and typically produce no symptoms. In most cases they resolve on their own without any treatment.1PubMed Central. A Rare Case of a Complex Nabothian Cyst in the Cervix: A Diagnostic Conundrum
Where nabothian cysts occasionally become noteworthy is when they grow unusually large. In rare cases, an enlarged nabothian cyst can press on surrounding structures and cause symptoms like pelvic pressure or difficulty with urination. These outliers can also create confusion on imaging, since a large complex cyst on the cervix raises questions about whether something more serious is going on. For the vast majority of people, though, nabothian cysts are incidental findings that require nothing more than a note in your chart.
Cystic Adenomyosis and Myometrial Cysts
Adenomyosis is a condition where tissue that normally lines the inside of the uterus grows into the muscular wall. Most people picture it as a diffuse thickening of the uterine wall, but it can also produce fluid-filled cysts within the muscle itself. These myometrial cysts are sometimes called cystic adenomyosis or cystic adenomyomas, and they form when pockets of displaced endometrial tissue become trapped and fill with blood or fluid. Histological examination of these cysts typically shows a multi-walled structure with a flattened lining and identifiable adenomyosis in the cyst wall and surrounding muscle.2Case Reports in Women’s Health. Myometrial cysts: A case series
These cysts tend to cause symptoms similar to adenomyosis itself: painful periods, heavy menstrual bleeding, and chronic pelvic pain. They can also be tricky to diagnose, since on ultrasound they may resemble fibroids, endometriomas, or other masses within the uterine wall. MRI is generally considered more useful than ultrasound for pinning down an adenomyosis diagnosis, with pooled sensitivity around 77% and specificity around 89% across studies.3Fertility and Sterility. Role of transvaginal sonography and magnetic resonance imaging in the diagnosis of uterine adenomyosis
Fibroids That Develop Cystic Changes
Uterine fibroids are solid growths of smooth muscle, not cysts. But fibroids can undergo what is called cystic or hydropic degeneration, and when they do, they start looking a lot like cysts on imaging. This happens when the cells in a growing fibroid outstrip their blood supply, causing portions of the tissue to die and liquefy into fluid-filled spaces.4Journal of Clinical Imaging Science. Magnetic resonance imaging findings of degenerating uterine fibroids: A pictorial review
On an MRI, a degenerating fibroid with cystic areas shows bright spots on certain imaging sequences, which can look confusingly similar to a true cyst or even a malignancy at first glance. The distinction matters because a simple cyst usually needs no treatment, while a degenerating fibroid might still be causing symptoms like pain, pressure, or heavy bleeding. Radiologists look for specific patterns to tell the difference, but occasionally the only way to get a definitive answer is surgical removal and a pathologist’s review.
Cystic Spaces in the Endometrial Lining
Ultrasound sometimes reveals small cyst-like pockets within the endometrium, the inner lining of the uterus. These cystic spaces can be caused by several things, but the most common association is with endometrial polyps, which are overgrowths of the lining that often contain dilated glands filled with fluid. A study from a tertiary center found that the presence of cystic spaces on ultrasound roughly doubled the odds of finding a polyp on biopsy. The same study found that cystic spaces were also associated with higher odds of a type of endometrial hyperplasia, but were actually linked to lower odds of endometrial cancer.5PubMed. Cystic Spaces in the Endometrium on Ultrasound and Correlations With Pathological Diagnosis: A Contemporary Retrospective Cohort Study in a Tertiary Centre
That last finding is reassuring but comes with an important caveat: it does not mean cystic spaces rule out cancer. It means that, statistically, their presence was associated with a lower probability of malignancy in that particular cohort. Your doctor will still consider your age, symptoms, endometrial thickness, and other imaging features before deciding whether biopsy is warranted. The cystic spaces are one piece of a larger puzzle.
Congenital Uterine Cysts in Young Women
Some uterine cysts are present from birth and only become apparent once a girl starts menstruating. The most recently recognized of these is called an accessory cavitated uterine malformation, or ACUM. It is a small extra cavity inside the uterine wall, lined with functioning endometrium but not connected to the main uterine cavity. Because the tissue inside this sealed-off pocket responds to monthly hormonal cycles with nowhere for the blood to go, it typically causes severe period pain starting soon after a girl’s first period.6PubMed Central. Accessory Cavitated Uterine Malformation (ACUM): An Underdiagnosed, Treatable Cause of Dysmenorrhea
A scoping review that pooled over a hundred reported cases found the median age at symptom onset was 17 years. On ultrasound, ACUM typically appears as a single-chambered cyst within the muscle wall, often with a ground-glass appearance suggesting old blood inside. MRI shows similar signs of hemorrhagic content.7PubMed Central. Accessory cavitated uterine malformation (ACUM): A scoping review The condition is considered rare, but researchers suspect it is underdiagnosed because it mimics more common problems like adenomyosis and fibroids. The good news is that surgically removing the accessory cavity is curative, and the rest of the uterus, tubes, and ovaries are typically normal.
ACUM is worth knowing about because teenagers and young women with unexplained, severe cramping that does not respond well to standard treatments sometimes cycle through years of misdiagnosis before someone identifies the accessory cavity on imaging. Awareness among both patients and clinicians can shorten that journey considerably.
Drug-Induced Cystic Changes
Certain medications can cause the uterine lining to develop cystic features. The best-documented example is tamoxifen, a drug widely used in breast cancer treatment. Tamoxifen has a complex relationship with the endometrium: while it blocks estrogen’s effects on breast tissue, it can act as a weak estrogen mimic in the uterus. Over time, this can lead to a condition called endometrial cystic atrophy, sometimes referred to as “tamoxifen mucosa,” where multiple cyst-like spaces lined by thin, atrophic endometrium develop within dense fibrous tissue.8PubMed Central. The effect of tamoxifen on the genital tract
On ultrasound, tamoxifen-related endometrial changes can look alarming because the lining appears thickened and cystic, raising concern about endometrial cancer or hyperplasia. But histologically, the tissue is often atrophic rather than actively growing. That said, tamoxifen does independently raise the risk of endometrial cancer over long-term use, so cystic endometrial changes in someone taking tamoxifen are not automatically benign. They usually prompt further evaluation, often a biopsy, to confirm what is actually going on at the cellular level.
Embryological Remnants Near the Uterus
During fetal development, certain embryological structures form and then regress. Occasionally, remnants of these structures persist and can develop into cysts near or within the cervix. Gartner’s duct cysts, for instance, arise from remnants of the mesonephric (Wolffian) duct and can appear in the vaginal wall or close to the uterine cervix. Small ones are often found incidentally and may be difficult to distinguish from nabothian cysts on ultrasound, particularly when using transabdominal imaging rather than a transvaginal approach.9Journal of Anesthesia & Critical Care: Open Access. A Case of Gartner’s Cyst of the Vagina
Paratubal cysts are another example of remnant-derived cysts that sit near the uterus. They grow from embryological tissue near the fallopian tubes and, while technically not inside the uterus itself, can present with pelvic pain and progressive abdominal swelling when they enlarge.10PubMed Central. Case Report: Successful laparoscopic approach for the management of a voluminous left paratubal cyst: two cases and a literature review These cysts are benign but can mimic ovarian cysts or other uterine masses on imaging, which is why precise imaging and sometimes surgical exploration are needed to sort them out.
How Uterine Cysts Are Found and Diagnosed
Most uterine cysts are discovered during a routine pelvic ultrasound, either a transvaginal scan or a transabdominal one. Transvaginal ultrasound is the workhorse of gynecological imaging: it is inexpensive, widely available, does not involve radiation, and it provides a close-up view of the uterus and surrounding structures. For conditions like ovarian endometriomas, transvaginal ultrasound has a sensitivity above 90%, meaning it catches the vast majority of cases.11PubMed Central. Transvaginal Ultrasound vs. Magnetic Resonance Imaging: What Is the Optimal Imaging Modality for the Diagnosis of Endometriosis?
Where ultrasound sometimes falls short is in characterizing what a cyst actually is. A cyst within the uterine wall could represent cystic adenomyosis, a degenerating fibroid, an accessory cavitated malformation, or something else entirely, and these can look similar on ultrasound. MRI becomes valuable here because it provides better contrast between tissue types. For detecting uterine enlargement and asymmetry, which help distinguish adenomyosis from fibroids, MRI outperforms ultrasound.12Medical Science Monitor. Efficacy of Transvaginal Ultrasound vs Pelvic MRI in Preoperative Diagnosis of Pelvic Endometriosis Your doctor may order an MRI when the ultrasound raises questions that need a more definitive answer before deciding on treatment.
One thing that occasionally creates confusion on imaging is a uterine arteriovenous malformation, which is a tangle of abnormal blood vessels in the uterine wall. On a standard gray-scale ultrasound, these can appear as tubular spaces or inhomogeneous areas within the muscle that might be mistaken for cysts. Doppler imaging, which detects blood flow, helps distinguish vascular anomalies from true fluid-filled cysts because the “spaces” in an arteriovenous malformation are actually channels of flowing blood.13PubMed. Uterine arteriovenous malformations: gray-scale and Doppler US features with MR imaging correlation
When a Uterine Cyst Might Be Something More Serious
The overwhelming majority of cystic findings in the uterus are benign. But in rare cases, a cystic-appearing mass can represent a malignancy. Endometrial stromal sarcoma, an uncommon uterine cancer, typically presents as a solid mass but can occasionally develop cystic features, including a multilocular cystic appearance that might be mistaken for a benign cyst on imaging.14PubMed. Cystic variant of endometrial stromal sarcoma: report of two cases This is genuinely rare, but it is the reason clinicians take a careful approach to cystic masses that have unusual features, like solid components mixed with cystic areas, irregular borders, or rapid growth.
There is no single imaging feature that definitively separates benign from malignant cystic lesions in the uterus. Instead, doctors weigh multiple factors: your age, symptoms, how the mass looks on ultrasound and MRI, whether it has changed over time, and your personal risk profile. A simple, thin-walled, fluid-filled cyst with no solid components and no abnormal blood flow is almost always benign. A complex, thick-walled, rapidly growing mass with mixed solid and cystic features warrants tissue sampling.
Effects on Fertility and Pregnancy
Whether a uterine cyst affects your ability to get pregnant depends entirely on what kind of cyst it is and where it sits. Nabothian cysts on the cervix have no meaningful impact on fertility. A small myometrial cyst from cystic adenomyosis might not affect conception at all if it is not distorting the uterine cavity, while more extensive adenomyosis can impair implantation and increase miscarriage risk.
For women with adenomyosis who are trying to conceive, a review of surgical approaches found that conservative surgery to remove affected tissue appears to improve fertility outcomes, whether or not it is combined with medical therapy. However, operating on the uterine wall carries its own risks, including a meaningful risk of uterine rupture during a future pregnancy, and the best surgical technique to minimize that risk has not been established.15PubMed Central. The Impact of Conservative Surgical Treatment of Adenomyosis on Fertility and Perinatal Outcomes The decision to operate before attempting pregnancy is highly individual and depends on the severity of symptoms, the extent of disease, and how long someone has been trying to conceive.
Congenital cystic conditions like ACUM are a separate consideration. Because the abnormal cavity is walled off from the rest of the uterus, it does not typically interfere with implantation in the normal uterine cavity. The review of reported ACUM cases noted that some affected women had already given birth, suggesting the condition does not preclude pregnancy.7PubMed Central. Accessory cavitated uterine malformation (ACUM): A scoping review Removal of the accessory cavity resolves pain and does not compromise the normal uterine structure.
Fluid Collections That Mimic Cysts
Sometimes what appears to be a uterine cyst is actually a collection of fluid inside the uterine cavity itself. Hematometra, for instance, is the accumulation of blood in the uterus, usually because something is blocking the outflow through the cervix. This can result from congenital abnormalities, scarring from previous surgery, or cervical stenosis. On imaging, a distended, fluid-filled uterus can superficially resemble a large cyst.16PubMed Central. A Rare Case of Recurrent Hematometra of Unknown Etiology The treatment is addressing the obstruction rather than the fluid itself, since the blood is a symptom of the blockage, not a standalone problem.
Postmenopausal women sometimes have small amounts of fluid in the uterine cavity detected on ultrasound. In most cases this is a benign finding related to cervical narrowing that slows the drainage of normal secretions. It does not typically represent a cyst, though it can prompt further evaluation to rule out endometrial pathology, particularly if the endometrial lining is also thickened.
Why “Uterine Cyst” Rarely Means What People Fear
When most people hear “cyst,” the mental image is something that needs to come out. The reality with uterine cysts is that the majority fall into the “leave it alone” category. Nabothian cysts are ignored unless they are enormous. Small myometrial cysts from adenomyosis are managed based on symptoms, not the cyst’s mere existence. Cystic spaces in the endometrium are evaluated in context and often turn out to be polyps, which are benign growths easily removed during a minor office procedure. Even the rarer conditions like ACUM are treatable with surgery that preserves the rest of the uterus.
The main challenge with uterine cysts is not danger but diagnostic clarity. Because so many different conditions can produce cyst-like findings in or near the uterus, getting to the right diagnosis sometimes requires more than one imaging study, and occasionally a biopsy or surgical exploration. If you have been told you have a cyst in your uterus, the most useful question to ask your doctor is not “is it dangerous” but “what kind of cyst is it,” since that determines everything from whether you need follow-up imaging to whether treatment makes sense.