Causes of Ovarian Cysts
The vast majority of ovarian cysts are functional cysts caused by normal ovarian follicular activity during the menstrual cycle, with a smaller proportion representing benign neoplasms such as endometriomas, dermoid cysts (mature cystic teratomas), and cystadenomas. 1
Functional Cysts
- Functional cysts are the most common type in premenopausal women, arising from perturbations in the hypothalamic-pituitary-gonadal axis during normal ovarian function 2, 3
- These cysts develop when normal follicular development goes awry—either a follicle fails to rupture and release an egg, or the corpus luteum fails to involute properly 3
- Functional cysts typically wax and wane over time or resolve spontaneously, particularly those less than 5 cm in diameter 1, 4
- Hemorrhagic functional cysts will decrease or resolve on sonographic follow-up in 8 to 12 weeks, distinguishing them from nonfunctional cysts which persist 1
Benign Neoplastic Cysts
Endometriomas:
- Result from ectopic endometrial tissue implanting on the ovary, causing blood-filled cysts 1, 5
- Commonly associated with endometriosis and cyclical pelvic pain 5
- May change appearance with age, losing the classic unilocular ground glass appearance 1
Dermoid cysts (mature cystic teratomas):
- Arise from germ cells and contain tissue from multiple embryonic layers 1
- Most likely type to cause ovarian torsion 4
Cystadenomas:
- Benign epithelial neoplasms that can be serous or mucinous 3
- Represent true neoplasms rather than functional processes 1
Other Cystic Lesions
- Paraovarian and paratubal cysts: Arise from embryologic remnants adjacent to the ovary 1
- Peritoneal inclusion cysts: Result from fluid trapped by peritoneal adhesions 1
- Hydrosalpinx: Fluid-filled fallopian tube, not truly an ovarian cyst but appears as an adnexal mass 1
Rare Causes
- Recurrent functional cysts syndrome: Characterized by persistent recurrence of symptomatic functional cysts, elevated plasma estradiol levels, and infertility, attributed to either increased gonadotropin production or hypersensitive response to normal gonadotropins 6
- Extraovarian tissue: In rare cases, ovarian-like tissue present within the pelvic cavity can become sensitive to circulating gonadotropins and form cysts 6
Important Clinical Context
- Simple cysts, regardless of size and menopausal status, are not associated with increased risk of cancer 1
- The risk of malignancy in benign-appearing lesions managed conservatively is only 0.3% to 0.4% 1
- In postmenopausal women, simple ovarian cysts have a malignancy rate of approximately 1 in 10,000 7
- Most ovarian cysts are asymptomatic and discovered incidentally on imaging 3, 5