Why do women develop large ovarian cysts?

Why Women Develop Large Ovarian Cysts

Most large ovarian cysts in women develop from normal physiological processes—specifically functional cysts (follicular or corpus luteum cysts) that fail to regress spontaneously—though size ≥10 cm substantially increases malignancy risk and warrants surgical evaluation regardless of appearance. 1

Physiological Mechanisms of Cyst Formation

Functional Cysts (Most Common Cause)

• Follicular cysts arise when a dominant follicle fails to rupture during ovulation, continuing to accumulate fluid and potentially growing beyond the typical 2-3 cm size. 2
• Corpus luteum cysts develop when the corpus luteum (formed after ovulation) fails to involute normally, instead filling with fluid or blood and persisting beyond the expected 2-week luteal phase. 3
• These functional cysts account for the majority of ovarian masses in premenopausal women and typically resolve spontaneously within 1-2 menstrual cycles without intervention. 3, 2
• Oral contraceptives do not accelerate resolution of functional cysts despite widespread historical use for this purpose; watchful waiting for 2-3 cycles is the appropriate management. 4

Why Some Cysts Become Large

• Most functional cysts remain ≤5 cm and resolve spontaneously, but a subset continues to enlarge beyond 5-10 cm when normal resorption mechanisms fail. 1, 2
• Cysts ≥10 cm carry substantially higher cancer risk regardless of sonographic appearance and should undergo surgical evaluation even when they appear benign. 1
• Persistent cysts that fail to resolve after 8-12 weeks are more likely to represent true neoplasms (benign or malignant) rather than functional lesions. 1, 5

Neoplastic Causes of Large Cysts

Benign Neoplasms

• Dermoid cysts (mature cystic teratomas) account for 20% of all ovarian tumors and are the most common ovarian tumor overall, often growing slowly to large sizes. 6
• Serous and mucinous cystadenomas are benign surface epithelial tumors that can reach substantial dimensions, particularly mucinous types which may grow to 10-30 cm. 7
• Endometriomas develop from ectopic endometrial tissue implanting on the ovary, forming blood-filled cysts that enlarge with repeated menstrual cycles. 1, 5

Age-Related Patterns

• In premenopausal women, functional cysts and dermoid cysts predominate, with germ cell tumors accounting for >75% of ovarian tumors in younger patients. 6
• In postmenopausal women, any new cyst is more concerning because functional cysts should not occur after ovulation ceases; persistent simple cysts >3 cm require at least 1-year follow-up. 5, 8
• The risk of malignancy in a symptomatic ovarian cyst increases from approximately 1:1,000 in premenopausal women to 3:1,000 at age 50. 2

Critical Clinical Distinctions

When Large Cysts Are Benign

• Simple cysts (completely anechoic, thin smooth walls <3 mm, no internal elements) have near-zero malignancy risk even when large: zero malignancies were found among simple cysts in women <50 years in a cohort of 12,957 cysts. 5
• In postmenopausal women, 46% of simple cysts resolve spontaneously and 44% persist unchanged; only 1.06% significantly increased in size over follow-up. 8
• Among 226 postmenopausal women with unilocular cysts <50 mm followed for 5 years, only 2 (0.9%) developed malignancy, both with elevated CA-125. 9

Red Flags for Malignancy

• Complex features including thick or irregular septations (≥3 mm), solid components, papillary projections, or high vascularity (color score 4) dramatically increase malignancy risk to 10-50% (O-RADS 4) or ≥50% (O-RADS 5). 1
• Size ≥10 cm is itself a risk factor requiring surgical evaluation regardless of other features. 1, 5
• Postmenopausal status with any complex features warrants immediate gynecologic oncology referral, as hemorrhagic cysts should not occur after menopause. 1, 5

Common Pitfalls to Avoid

• Do not operate on simple functional cysts <10 cm in premenopausal women—even large simple cysts have only 0.5-0.6% malignancy risk and most resolve with observation. 5
• Do not assume all persistent cysts are pathological—many benign neoplasms (dermoids, endometriomas) can be safely followed with annual surveillance. 5
• Do not underestimate malignancy risk based on size alone—cysts ≥10 cm require surgical evaluation even when appearing benign on imaging. 1
• Ensure gynecologic oncology involvement when malignancy is suspected; only 33% of ovarian cancers are appropriately referred initially, yet oncologist involvement is the second most important prognostic factor after stage. 1