An ovarian cystadenoma is a benign epithelial tumor that arises from the surface cells of the ovary. Cystadenomas are among the most common noncancerous ovarian tumors in reproductive-age and perimenopausal women. Unlike functional cysts that resolve with the menstrual cycle, cystadenomas are true neoplasms that persist and can grow quite large before being discovered — and they lie on a biological continuum with borderline tumors and ovarian cancer that makes accurate MRI characterization essential.
Ovarian cystadenomas occupy a critical position in the differential diagnosis of ovarian cystic masses — they must be distinguished from benign functional cysts that require only observation, and from ovarian cancer and borderline ovarian tumors that require prompt oncologic surgery. A serous cystadenoma is histologically related to serous ovarian carcinoma — the most common type of ovarian cancer — and the two can share imaging features. MRI with the O-RADS scoring system provides standardized risk stratification that guides appropriate management. Cystadenomas should also be distinguished from endometriomas, dermoid cysts, and hemorrhagic functional cysts — all of which can produce a similar clinical picture of an incidentally discovered ovarian mass.
Causes
Epithelial cell proliferation.
Cystadenomas develop from abnormal but controlled proliferation of the surface epithelium — the single cell layer covering the ovary and lining its inclusion cysts — which is the same cell layer that gives rise to the majority of ovarian cancers. Unlike functional cysts, which form as a consequence of normal ovulatory physiology and resolve spontaneously, cystadenomas are true neoplasms: they grow indefinitely, do not regress with hormonal changes, and will continue to enlarge if not removed. The cells lining the cyst cavity actively secrete fluid — serous (thin, watery) in serous cystadenomas and mucin (thick, gelatinous) in mucinous cystadenomas — which accumulates progressively within the cyst. The continuous fluid secretion explains why mucinous cystadenomas in particular can reach enormous sizes — occasionally exceeding 30 cm and filling the entire peritoneal cavity — before producing symptoms significant enough to prompt evaluation.
Other contributing factors.
The precise molecular drivers of cystadenoma development are incompletely understood. Risk factors for epithelial ovarian tumors broadly include nulliparity, advancing age, and a family history of ovarian or breast cancer — though cystadenomas most commonly develop without identifiable risk factors and in the absence of BRCA mutations, which are more strongly associated with high-grade serous carcinoma. They occur most frequently between ages 30 and 60, encompassing the late reproductive and perimenopausal years. Pregnancy and long-term oral contraceptive use appear to reduce the risk of epithelial ovarian tumors generally, possibly through their suppression of repetitive ovulation-related epithelial trauma.
Symptoms
Small cystadenomas are frequently asymptomatic and discovered incidentally during pelvic examination or on ultrasound or MRI performed for unrelated indications. Because cystadenomas do not produce hormonal changes and many reach substantial size before causing symptoms, the diagnosis is often made in an asymptomatic woman whose cyst is large enough to be palpable on examination or visible on imaging. Larger cystadenomas produce pelvic and lower abdominal pressure, bloating, early satiety from upward displacement of the stomach, and a visible or palpable abdominal mass. Urinary frequency or urgency develops when anterior cysts compress the bladder, and constipation when posterior cysts press on the rectosigmoid colon. Dyspareunia may be present. Ovarian torsion — the ovary twisting on its vascular pedicle due to the weight and mobility of the cyst — is a significant risk with larger cystadenomas and presents as sudden, severe, unilateral pelvic pain requiring emergency surgery. Cyst rupture can release fluid into the peritoneal cavity; mucinous cystadenoma rupture carries the additional risk of pseudomyxoma peritonei — the filling of the peritoneal cavity with mucin-secreting implants — a serious and difficult-to-treat condition.
Diagnosis
Pelvic ultrasound identifies the presence of an ovarian cystic mass and provides initial morphologic assessment. Serous cystadenomas typically appear as large, thin-walled, anechoic or lightly septated unilocular cysts. Mucinous cystadenomas are characteristically multilocular — multiple compartments with variable internal echo levels reflecting the heterogeneous mucin content. However, ultrasound cannot reliably distinguish a benign cystadenoma from a borderline tumor or early ovarian carcinoma, particularly when the cyst contains septations or papillary projections.
An MRI of the pelvis is the most accurate characterization study and is essential for surgical planning and risk stratification. MRI allows comprehensive evaluation of internal architecture — thin vs. thick septations, the presence and enhancement characteristics of mural nodules or papillary projections, the signal intensity of the fluid (T2-bright watery fluid in serous vs. variable T1/T2 signal in mucinous), and the relationship of the mass to the uterus, bladder, and bowel. The critical MRI findings that distinguish a benign cystadenoma from a borderline or malignant tumor are the presence of enhancing solid components — papillary projections or mural nodules with contrast enhancement on post-gadolinium sequences and restricted diffusion on DWI — which indicate active tumor proliferation. The O-RADS MRI scoring system provides a standardized 1–5 risk score based on these morphologic features, with Scores 1–2 indicating essentially benign lesions safe for observation, Score 3 warranting close follow-up, and Scores 4–5 indicating high malignancy risk requiring surgical evaluation. MRI also identifies bilateral ovarian involvement (more common with serous cystadenomas), peritoneal disease, lymphadenopathy, and ascites that would indicate advanced malignancy.
Classification
Ovarian cystadenomas are classified by the type of epithelium and fluid content, and by their degree of cellular atypia — a spectrum that extends from clearly benign to borderline to frankly malignant.
- Serous cystadenoma: Lined by tubal-type epithelium secreting thin watery fluid. Typically unilocular, thin-walled, and unilateral though bilaterality occurs in 10–20%. Often discovered at smaller sizes. The most common benign ovarian neoplasm. Histologically related to serous ovarian carcinoma — the most lethal form of ovarian cancer — making careful imaging assessment essential.
- Mucinous cystadenoma: Lined by mucin-secreting endocervical-type or intestinal-type epithelium. Characteristically multilocular with variable internal signal reflecting differing mucin concentrations in different locules (the "stained glass" appearance on MRI). Tends to be unilateral and can reach enormous sizes. Rupture risk is greater with increasing size, and rupture of a mucinous tumor carries the risk of pseudomyxoma peritonei.
- Borderline (low malignant potential) cystadenoma: Epithelial proliferation exceeding that of a benign cystadenoma without stromal invasion. An intermediate category requiring surgical removal and long-term surveillance. Can recur or rarely progress to invasive carcinoma. MRI may show papillary projections that are not definitively distinguishable from invasive cancer without histologic examination.
Treatments
Treatment depends on cystadenoma type and size, imaging risk stratification (O-RADS score), symptoms, patient age, and menopausal status.
Observation: Small, morphologically simple-appearing cystadenomas in premenopausal women with low O-RADS scores may be monitored with periodic ultrasound or MRI, particularly when the patient is asymptomatic and the features are reassuringly benign. However, because cystadenomas grow continuously and do not resolve, the threshold for surgical removal is lower than for functional cysts — any cyst that is enlarging on serial imaging or causing symptoms warrants removal regardless of initial MRI risk score.
Surgical removal.
Surgical removal is recommended for cystadenomas that are large (typically over 5–7 cm), growing on serial imaging, symptomatic, have elevated O-RADS scores suggesting borderline or malignant features, or occur in postmenopausal women. Laparoscopic cystectomy — removing only the cyst while preserving the ovarian cortex — is the preferred approach for younger women with premenopausal fertility goals when the surgical planes allow it. Care must be taken not to rupture the cyst during laparoscopic removal, as rupture of a mucinous cystadenoma risks peritoneal contamination with mucin-secreting epithelium. Laparoscopic or open oophorectomy is performed when cystectomy is not technically feasible, when the ovary has been destroyed by the cyst, or when postmenopausal status makes ovarian preservation less critical. When borderline or malignant features are identified intraoperatively, frozen section is requested, and gynecologic oncology is involved for staging procedures.
Pathologic evaluation.
Every surgically removed cystadenoma requires pathologic examination by a pathologist to confirm benign histology and definitively exclude borderline or malignant features — imaging alone cannot always make this distinction with certainty, and treatment decisions after surgery depend entirely on the histologic diagnosis. Benign cystadenomas require no further oncologic management. Borderline tumors require complete surgical staging and periodic surveillance imaging. Malignant tumors require comprehensive gynecologic oncologic management.
Get an MRI to Confirm Your Diagnosis
Before surgical planning or starting treatment, a clear MRI diagnosis ensures the right path forward. First Look MRI offers self-pay Pelvis MRI scans — no doctor's order or insurance required — at our locations in Georgia, Texas, and Colorado.