A multiloculated ovarian cyst is a fluid-filled growth on or within the ovary that contains internal walls, called septa, dividing it into multiple compartments or “locules.” The finding shows up frequently on pelvic ultrasounds and, by itself, does not mean cancer. Most multiloculated cysts turn out to be benign, but their internal complexity is exactly what prompts doctors to look more closely than they would at a plain, single-chambered cyst. The difference between a reassuring outcome and a concerning one often comes down to a handful of specific imaging features and how the cyst behaves over time.
What “Multiloculated” Actually Means on an Imaging Report
A simple ovarian cyst is a single fluid-filled sac with thin, smooth walls. When a cyst is described as multiloculated (sometimes written “multilocular”), it has thin or thick internal dividers that create separate pockets of fluid. Think of it like a grapefruit rather than a balloon: cut it open and you see sections. The number and thickness of those internal walls matter because they influence how likely the cyst is to be something that needs treatment versus something that will resolve on its own.
Imaging reports typically classify ovarian masses into five broad categories: unilocular cyst, unilocular solid cyst, multilocular cyst, multilocular solid cyst, and solid tumor. A multilocular cyst without any solid areas sits in the middle of that spectrum. When solid components are present alongside the multiple compartments, the mass gets bumped into the “multilocular solid” category, which raises the level of concern.
Common Causes, from Harmless to Worrisome
The list of things that can produce a multiloculated appearance on ultrasound is surprisingly long. Most of them are benign.
- Mucinous cystadenoma: A benign tumor filled with thick, gel-like fluid. These tend to grow large, sometimes dramatically so, and their multiloculated structure is one of their hallmarks. Symptoms are often vague: bloating, mild abdominal pain, nausea, or fatigue that can easily be mistaken for other conditions.1PubMed Central. Mucinous Cystadenoma of Ovary with Vague Symptoms: A Case Report
- Serous cystadenofibroma: A benign growth that can appear as a multilocular cyst in roughly one in five cases. These often show little to no blood flow on Doppler imaging and may cast an acoustic shadow on ultrasound, both of which help distinguish them from something more aggressive.2PubMed. Imaging in gynecological disease (16): clinical and ultrasound characteristics of serous cystadenofibromas in adnexa
- Mature cystic teratoma (dermoid cyst): Usually described as unilocular, but about 15% present as multilocular cysts. They contain a mix of tissue types, so the ultrasound often shows mixed echogenicity and shadowing.3PubMed. Imaging in gynecological disease (24): clinical and ultrasound characteristics of ovarian mature cystic teratomas
- Endometrioma: An “ovarian chocolate cyst” caused by endometriosis. Most are unilocular with a characteristic ground-glass appearance, but multiloculated versions exist and can sometimes fool imaging specialists into suspecting something worse.4PubMed Central. Imaging in gynaecology: How good are we in identifying endometriomas?
- Functional cysts that have bled or partially resolved: Sometimes a hemorrhagic corpus luteum or a cyst that has partially collapsed develops internal strands or walls of clot that mimic true septa on a quick scan.
Less commonly, a multiloculated ovarian mass can represent a borderline tumor or, more rarely, an invasive cancer. These possibilities are why doctors do not simply ignore the finding.
Septated Cysts and Cancer Risk
One of the largest studies to directly address this question tracked over 1,300 women with septated (internally divided) ovarian cysts. Among nearly 2,900 tumors, about 39% resolved on their own over an average of twelve months. Of those that were surgically removed, the most common findings were serous cystadenoma, mucinous cystadenoma, and endometrioma. Only one borderline tumor was found, and there were zero cases of invasive ovarian cancer.5PubMed. Risk of malignancy in sonographically confirmed septated cystic ovarian tumors That study focused on cysts whose septa were thin and whose compartments were purely fluid-filled, without solid lumps or thick walls. In other words, a multiloculated cyst that is otherwise “quiet” on imaging carries a very low malignancy risk.
The picture changes when other features pile on. Suspicion for malignancy climbs with the patient’s age, the size of the mass, the presence of solid components or thick septa, and the amount of blood flow detected on color Doppler.6PubMed Central. Spectrum of Ovarian Incidentalomas: Diagnosis and Management A multiloculated cyst in a 30-year-old with thin septa, no solid areas, and no abnormal blood flow is a completely different clinical situation from a multilocular solid mass in a 65-year-old with thick, irregular walls.
How Doctors Decide What to Do Next
When a multiloculated cyst is found, clinicians rely on structured scoring systems, blood tests, and sometimes MRI to figure out whether watching and waiting is safe or whether surgery is needed.
Ultrasound Scoring Systems
The most widely used frameworks right now are O-RADS (Ovarian-Adnexal Reporting and Data System) and GI-RADS, both of which assign a risk category from 1 (almost certainly normal) to 5 (high suspicion for cancer). A multiloculated cyst without solid parts or increased blood flow usually lands in an intermediate category, prompting follow-up imaging rather than immediate surgery. Studies show these systems have strong sensitivity for catching malignancy, with one prospective trial reporting that both GI-RADS and O-RADS achieved 100% sensitivity at the threshold used to flag potential malignancy.7PubMed. Diagnostic performance of ultrasound reporting systems in evaluation of adnexal masses: A prospective observational study The tradeoff is specificity: some benign masses get flagged as suspicious, which leads to further workup or unnecessary anxiety.
Blood Markers
CA-125 is the most familiar blood test for ovarian masses, but it is far from perfect on its own: it can be elevated by endometriosis, fibroids, liver disease, and even menstruation. A newer marker called HE4 tends to be more specific. When HE4 and CA-125 are combined with MRI, one study found the diagnostic accuracy for distinguishing benign from malignant ovarian tumors reached about 97%.8Journal of Radiation Research and Applied Sciences. Serum CA125 and HE4 levels combined with magnetic resonance imaging (MRI) in the clinical diagnostic value of ovarian neoplasms In practice, your doctor may order one or both markers to help interpret an ambiguous ultrasound.
MRI for Difficult Cases
When ultrasound alone cannot settle the question, MRI adds more detail. It can show the exact thickness of septa, distinguish clot from true solid tissue, and characterize the fluid in each compartment. For mucinous borderline tumors specifically, MRI tends to show large multilocular masses with a honeycomb pattern, locules that differ in signal brightness, and walls or septa thicker than about 3 mm.9PubMed. MRI appearances of mucinous borderline ovarian tumors: pathological correlation These features help radiologists separate a borderline growth from a benign cystadenoma, where the septa tend to be thinner and more uniform.
Borderline Tumors and the Mucinous Spectrum
Mucinous ovarian tumors deserve special mention because they span a full spectrum from completely benign cystadenoma, through borderline (low malignant potential), to frankly invasive cancer. Unlike the more common high-grade serous ovarian cancers, mucinous tumors appear to progress along a continuum, and their molecular profile is distinct: mutations in KRAS are common, while BRCA and p53 mutations are rare.10PubMed Central. Mucinous tumors of the ovary: current thoughts on diagnosis and management This matters because it affects prognosis and treatment decisions.
A borderline mucinous tumor can look like a benign cystadenoma on imaging, especially when it lacks obvious solid areas. The key MRI clues include heterogeneous signal across locules (different compartments lighting up differently because the mucin inside them varies in concentration) and slightly thickened septa.11PubMed. MRI appearances of mucinous borderline ovarian tumors: pathological correlation Borderline serous tumors, meanwhile, tend to show prominent papillary projections branching from the cyst wall, which are more conspicuous on both ultrasound and MRI.12PubMed. MRI appearances of ovarian serous borderline tumor: pathological correlation
The good news is that borderline tumors, as a group, have an excellent prognosis when caught at an early stage. Surgery is typically the primary treatment, and for younger patients who want to preserve fertility, removing just the affected ovary is often sufficient.
Multiloculated Masses in Pregnancy
Finding an ovarian mass during pregnancy is unsettling, and the multiloculated appearance adds to the worry. Data from one study that classified ovarian masses discovered during pregnancy by their ultrasound shape found that purely multilocular cysts had a 27% rate of malignancy on final pathology, multilocular solid masses had a 70% rate, while unilocular cysts had 0%.13International Journal of Gynecological Cancer. Management of ovarian masses in pregnancy: patient selection for interventional treatment Those numbers are higher than what you would see in non-pregnant populations because the study specifically looked at masses that were concerning enough to warrant surgical removal, not all ovarian cysts found incidentally during pregnancy.
Most simple cysts found in early pregnancy are corpus luteum cysts and resolve by the second trimester. Persistent or complex masses may require surgery, and laparoscopic removal has been shown to be safe even at advanced gestational ages. In one case series, all patients who underwent emergency laparoscopy for ovarian cysts during pregnancy delivered after 37 weeks with no fetal complications.14PubMed Central. Laparoscopic management of ovarian cysts during pregnancy under urgent situations Ovarian torsion was the most common reason the surgery could not wait.
A separate condition that can mimic a multiloculated ovarian mass during pregnancy is hyperreactio luteinalis, a rare hormonal response where luteal tissue proliferates into multiple cysts on both ovaries. It is driven by elevated levels of hCG, the pregnancy hormone, and typically resolves on its own after delivery.15PubMed. Hyperreactio luteinalis: timely diagnosis minimizes the risk of oophorectomy and alerts clinicians to the associated risk of placental insufficiency Recognizing it matters because removing the ovaries in this situation is unnecessary and can be avoided with a correct diagnosis.
Ovarian Torsion and Other Acute Complications
Any ovarian cyst, including a multiloculated one, can cause the ovary to twist on its blood supply, a surgical emergency called ovarian torsion. The larger and heavier the cyst, the greater the risk. In one documented case, a 28-year-old with a multiloculated cyst presented with sudden left-sided abdominal pain. At surgery, the fallopian tube and ovary were found twisted three times and had already become gangrenous, requiring removal of the tube and ovary.16Journal of Health and Translational Medicine. DIAGNOSING OVARIAN TORSION IN THE EMERGENCY DEPARTMENT: A CASE REPORT AND LITERATURE REVIEW
Torsion is notoriously difficult to diagnose because its symptoms overlap with many other conditions: sudden pelvic pain, nausea, vomiting. Doppler ultrasound can sometimes show reduced blood flow to the ovary, but a normal Doppler does not rule it out. If you have a known ovarian cyst and develop acute, severe one-sided pelvic pain, that warrants immediate medical attention.
Surgery and Preserving Healthy Ovarian Tissue
When a multiloculated cyst needs to come out, the surgical approach depends on its size, the suspicion for malignancy, and whether preserving ovarian function matters to the patient. In young women and children, the priority is almost always to save as much healthy ovarian tissue as possible. Ovarian-sparing laparoscopy is the standard approach for cysts that appear benign on imaging.17PubMed Central. The Evaluation, Diagnosis, and Management of Ovarian Cysts, Masses, and Their Complications in Fetuses, Infants, Children, and Adolescents
One practical challenge with multiloculated cysts, especially mucinous ones, is avoiding spillage of cyst contents into the abdomen during removal. If the cyst turns out to be borderline or malignant, intraperitoneal spill can potentially worsen staging. Techniques have been developed to address this. One method involves gluing a surgical sheet to the cyst surface before puncturing it, then aspirating the fluid under controlled conditions. For multilocular cysts specifically, the surgeon can puncture internal dividers one by one under direct vision after part of the cyst has been brought outside the body.18PubMed Central. Surgical technique to prevent spillage of cyst fluid during operation for cystic ovarian tumors Even very large mucinous cysts can be managed laparoscopically with careful drainage to avoid spillage.19PubMed Central. Laparoscopic management of a giant mucinous benign ovarian mass weighing 10150 grams: A case report
What Cyst Surgery Means for Fertility
Removing a cyst from an ovary inevitably means removing some healthy tissue along with it. Doctors use anti-Müllerian hormone (AMH), a blood marker of remaining egg supply, to gauge the impact. Multiloculated cysts are associated with a larger decline in AMH after cystectomy compared to simple cysts, likely because they are larger and take longer to dissect, which means more tissue is handled and potentially damaged.20PubMed Central. What is the role of robotic surgery in ovarian cystectomy with fertility preservation?
The type of cyst matters as much as its complexity. After laparoscopic cystectomy, endometriomas and dermoid cysts both caused significant drops in AMH, while serous and mucinous cysts did not produce a statistically meaningful decline.21PubMed Central. Effects of ovarian cyst types on ovarian reserve after three-dimensional laparoscopic cystectomy So a multiloculated mucinous cystadenoma, despite its intimidating ultrasound appearance, may be kinder to your egg reserve after surgery than a smaller endometrioma.
How the surgeon handles bleeding inside the ovary after cyst removal also affects outcomes. Using electrocautery to stop bleeding can damage nearby follicles. One trial found that using a hemostatic agent instead of standard cautery preserved more AMH, particularly in patients with endometriosis.22Scientific Reports. A randomized controlled trial of ovarian reserve preservation and hemostasis during ovarian cystectomy If fertility is a concern, it is worth discussing hemostasis techniques with your surgeon before the procedure.
Conditions That Mimic a Multiloculated Ovarian Cyst
Not every multiloculated pelvic mass actually originates from the ovary. One well-known mimic is the peritoneal inclusion cyst, a collection of fluid trapped by adhesions in the tissue lining the abdomen. These tend to occur in women who have had previous pelvic surgery or inflammation and are most common around menopause. On imaging, they can look strikingly similar to a multiloculated ovarian cyst, and they are often misdiagnosed as ovarian tumors.23PubMed Central. Multilocular peritoneal inclusion cyst mimicking an ovarian tumor: A case report A hydrosalpinx, where a blocked fallopian tube fills with fluid and develops compartments, can also mimic a multiloculated ovarian mass on ultrasound.24PubMed. Peritoneal inclusion cysts and their relationship to the ovaries: evaluation with sonography
These look-alikes matter because their treatment is different. A peritoneal inclusion cyst does not carry a malignancy risk and may be managed with aspiration or observation. A hydrosalpinx requires its own evaluation, especially in someone trying to conceive. MRI can usually sort out the origin of the mass when ultrasound leaves doubt.
The Emotional Side of an Ambiguous Diagnosis
Being told you have a “complex” or “multiloculated” ovarian mass, then being sent home to wait for follow-up imaging or additional tests, is genuinely stressful. Research on women diagnosed with adnexal masses confirms what common sense suggests: the experience negatively affects emotional well-being, daily life, and social functioning, especially when the possibility of malignancy looms in the background.25PubMed. Feelings, thoughts and experiences of women diagnosed with adnexal mass: A qualitative study Women in these studies reported relying heavily on their own internal coping resources and having lower expectations of professional support than they needed.
If you find yourself in this situation, asking your doctor to walk you through the specific imaging features driving their level of concern can help. The difference between “multiloculated cyst, thin septa, no blood flow” and “multilocular solid mass with thick irregular walls and high vascularity” is enormous in terms of what it likely means, but both can end up described vaguely as a “complex cyst” in casual conversation. Getting the details can turn an open-ended worry into a more bounded one.