A cystadenoma is a benign (noncancerous) tumor that grows as one or more fluid-filled sacs lined with a layer of cells called epithelium. These tumors most commonly develop in the ovaries but can also appear in the pancreas, liver, and appendix. Because they are cystic, meaning hollow and filled with fluid, they can grow quite large before causing any noticeable symptoms.
Where Cystadenomas Develop
The ovary is by far the most common site. Epithelial tumors account for about 60% of all ovarian tumors and 40% of benign ones, and cystadenomas make up a large share of that group. They occur predominantly in adult women, though rare cases have been reported in adolescents.
In the pancreas, cystadenomas tend to appear as clusters of small cysts that give the mass a honeycomb-like look on imaging. On CT scans, pancreatic serous cystadenomas typically have a lobulated contour (seen in over 90% of cases) and lack the solid nodules that would raise concern for a more aggressive growth. Cystadenomas can also form in the bile ducts of the liver, where they are considered premalignant and are usually removed promptly.
Serous vs. Mucinous Types
The two main varieties are named for the type of fluid they contain. Serous cystadenomas are filled with thin, watery fluid. In the ovary, benign serous tumors represent about 16% of all ovarian epithelial tumors and account for roughly two-thirds of the benign ones. They tend to be smaller and often have a single fluid-filled chamber.
Mucinous cystadenomas contain thicker, gel-like fluid. They can grow dramatically larger than serous types, sometimes reaching 30 centimeters or more. Benign mucinous cystadenomas account for 80% of all ovarian mucinous tumors. Because of their size potential, they are more likely to cause symptoms from sheer mass effect on surrounding organs.
A third, less common subtype called endometrioid cystadenoma makes up only 2 to 4% of ovarian tumors.
Symptoms and How They’re Found
Many cystadenomas cause no symptoms at all and are discovered incidentally during an ultrasound or CT scan done for another reason. When symptoms do appear, they are usually related to the physical size of the growth rather than any hormonal or chemical effect.
Common complaints include a feeling of fullness or bloating, gradually increasing abdominal distension, and a dull pelvic or abdominal ache that may worsen with movement. In one documented case, a mucinous cystadenoma grew to 30 centimeters, causing visible abdominal swelling and upper abdominal pain in a 28-year-old woman over the course of about two months. Larger growths can also press on the bladder or bowel, leading to urinary frequency or changes in bowel habits. In rare cases, an ovarian cystadenoma can cause the ovary to twist on its blood supply, a condition called ovarian torsion, which produces sudden, severe pain.
How Cystadenomas Are Diagnosed
Imaging is the first step. Transvaginal ultrasound is the go-to tool for ovarian cystadenomas, while CT and MRI are more commonly used for pancreatic and liver lesions. Doctors look at specific features to distinguish a simple, benign cyst from something more concerning: wall thickness, the presence of internal dividers (called septations), whether the walls show increased blood flow, and whether there are any solid nodules inside the cyst. A smooth, thin-walled cyst with no solid components is reassuring for a benign cystadenoma.
For pancreatic cystadenomas, radiologists look for that characteristic lobulated shape, check for central calcifications, and confirm the absence of solid nodules along the cyst wall. In one study, 100% of serous pancreatic cystadenomas had no mural nodules, which helped differentiate them from mucinous types that carry a higher risk of becoming cancerous.
Malignant Potential
Ovarian cystadenomas carry an excellent prognosis. They are benign, and the risk of a serous ovarian cystadenoma transforming into cancer is very low. Mucinous ovarian cystadenomas also have a favorable outlook, though they warrant monitoring because a small percentage of mucinous ovarian tumors fall into a “borderline” category between benign and malignant.
The picture is different for cystadenomas in the bile ducts of the liver. Biliary cystadenomas are considered premalignant, with a reported malignant transformation rate as high as 30%. For this reason, surgical removal is generally recommended once a biliary cystadenoma is suspected, regardless of whether it is causing symptoms.
Treatment Options
Small, asymptomatic ovarian cystadenomas that look clearly benign on imaging can often be monitored with repeated transvaginal ultrasounds rather than operated on right away. This watch-and-wait approach is especially common for smaller cysts discovered incidentally.
Surgery becomes the recommended path when a cystadenoma is large, growing, causing symptoms like pelvic pain or urinary pressure, or when imaging features are not entirely reassuring. In younger patients who want to preserve fertility, surgeons typically remove just the cyst (cystectomy) while leaving the rest of the ovary intact. For older patients or very large tumors, removing the entire ovary may be more practical. Both approaches can often be done laparoscopically, meaning smaller incisions and a shorter recovery.
For pancreatic serous cystadenomas that are small and clearly benign on imaging, observation with periodic scans is standard. Pancreatic mucinous cystadenomas, on the other hand, are more often removed because of their higher potential to become cancerous over time.
Recurrence and Long-Term Outlook
Recurrence after complete surgical removal is very rare. Ovarian cystadenomas seldom come back even after incomplete resection, which speaks to their low-grade, nonaggressive biology. That said, follow-up imaging is still recommended, particularly for younger patients who had a cystectomy rather than full ovary removal. Transvaginal ultrasound every 3 to 6 months is currently considered the most effective monitoring tool in this group.
Overall, the long-term prognosis for cystadenomas is excellent. Most people who have one removed or monitored go on without complications. The key distinction worth remembering is location: ovarian and pancreatic serous cystadenomas are overwhelmingly benign, while biliary cystadenomas in the liver carry meaningful cancer risk and should be treated more aggressively.