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Follicular Cyst

What It Is, Causes, Signs, Symptoms, and More

Author:Georgina Tiarks

Editors:Alyssa Haag,Emily Miao, PharmD,Kelsey LaFayette, DNP, ARNP, FNP-C,Jessica Reynolds, MS

Copyeditor:Stacy Johnson, LMSW


What is a follicular cyst?

Follicular cysts are physiologic, or functional, cysts that develop on the ovary due to incomplete rupture during ovulation. During the female reproductive cycle, a dominant follicle grows in the ovary. Typically, ovulation stimulates the rupture of this follicle and the release of an egg. However, in cases where the follicles are unruptured, follicular cysts occur. The fluid inside the follicle forms a cyst and may continue to grow. While many follicular cysts are asymptomatic, others can cause pelvic pain. Follicular cysts are the most common ovarian mass in young individuals assigned female at birth.

Other types of ovarian cysts include theca lutein cysts, corpus luteum cysts, endometrial chocolate cysts, dermoid cysts, or neoplastic cysts.

Incomplete rupture of a cyst on an ovary during ovulation.

What causes follicular cysts?

A follicular cyst is caused by incomplete rupture and reabsorption after ovulation. The menstrual cycle has two phases: the follicular phase and the luteal phase, which are separated by ovulation. During the follicular phase, follicle-stimulating hormone (FSH) is released from the anterior pituitary gland, which stimulates ovarian follicles to mature. While several follicles prepare for maturation, typically only one dominant follicle matures to ovulation. This dominant follicle produces estradiol; and once the estradiol has reached its peak, the hypothalamus releases gonadotropin-releasing hormone (GnRH), which then causes the anterior pituitary to produce a surge of luteinizing hormone (LH). The LH surge stimulates the ovulation of the egg from the dominant follicle. The dominant follicle typically ruptures to release the egg into the fallopian tubes. However, sometimes the egg is released without rupture of the follicle, which causes a follicular cyst to form.

Commonly, polycystic ovarian syndrome (PCOS) is associated with the development of multiple follicular cysts. PCOS is a hormonal condition characterized by cyst development in the ovaries, ovulatory dysfunction, and excess androgen production. While the exact cause of PCOS is unknown, studies have shown a complex interaction between androgens and estrogen. These hormonal imbalances cause follicular arrest, thereby leading to cyst development.

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What are the signs and symptoms of follicular cysts?

Follicular cysts are typically asymptomatic. Often, these follicular cysts can remain small and undetected until they spontaneously resolve, usually within three months. In some cases, they can be an incidental finding on imaging studies, like an ultrasound, or detected during palpation of the ovaries during a pelvic exam. However, in some cases, follicular cysts can continue to grow and become symptomatic. Larger cysts may cause unilateral, achy pelvic pain and dyspareunia (i.e., pain with sexual intercourse). It may also cause abnormal uterine bleeding from hormonal irregularities (e.g., estrogen production may be affected, which may impact the growth and shedding of the endometrial lining). Other complications of large cysts include rupture; hemorrhage; and ovarian torsion, which is twisting of the ovary around its support structures, thereby cutting off its blood supply. These are typically gynecological emergencies.

How are follicular cysts diagnosed?

Follicular cysts may be diagnosed by a clinician after a thorough medical history and physical examination. In some cases, an asymptomatic follicular cyst may be detected during a bimanual exam or palpation of the ovaries. If the clinician palpates an abnormality on the ovaries, they may recommend an ultrasound for further evaluation. If an individual is symptomatic with pain, a clinician may also want to order a pregnancy test to rule out ectopic pregnancy, urinalysis to assess for cystitis, and endocervical swabs to evaluate for sexually transmitted infections in addition to an ultrasound.

An ultrasound can be used to detect differences between simple and complex cysts. Simple cysts appear anechoic, unilocular, thin-walled, and smooth; whilst complex cysts may be larger, multilocular with septations, and contain solid components. A simple cyst is indicative of a more benign process, whereas a complex cyst can suggest ovarian cancer. A Doppler ultrasound may also be performed to assess for proper blood flow to the ovary to rule out ovarian torsion. Often, a repeat ultrasound is recommended to make sure the cyst has resolved and has not grown larger or has changed. However, this depends on the features and size of the cyst and age of the individual. For most simple cysts less than five centimeters in size in premenopausal women, no follow-up imaging is typically required. For cysts between five to seven centimeters, a yearly ultrasound can be performed. For cysts seven centimeters and greater, additional imaging, such as a CT, may be required. For postmenopausal women, a simple cyst less than five centimeters with low risk of malignancy can be reevaluated in four to six months. However, if the cyst has any concerning features, has a positive CA-125 blood test (i.e., tumor marker), or is symptomatic, additional imaging may be recommended.

How are follicular cysts treated?

Follicular cysts are treated based on associated symptoms and physical characteristics. A young, premenopausal individual with small, asymptomatic cysts and no concerning features may be treated with over-the-counter pain relief as needed (e.g., NSAIDs) and a repeat ultrasound a few months later if necessary. In those individuals, there is a low risk of malignancy based on the age, menopausal status, and features of the cyst. A small, benign follicular cyst has a good chance of spontaneous resolution without intervention. However, in older individuals who are postmenopausal with cysts exhibiting concerning features, additional treatment may be warranted, which can include an oophorectomy (i.e., a surgery to remove an ovary). Biopsies of the ovary are not recommended as it can cause malignant cells to disperse into the peritoneum, potentially seeding into the abdominal cavity. Oral contraceptives may also be prescribed to help to regulate the menstrual cycle and prevent future cyst development.

What are the most important facts to know about follicular cysts?

Follicular cysts, also known as functional or physiologic cysts, develop when a dominant follicle does not rupture and reabsorb. During the menstrual cycle, a dominant follicle is selected to mature and eventually rupture and release an egg. However, follicular cysts accumulate fluid without rupturing. In many situations, follicular cysts are asymptomatic. However, symptoms of an ovarian cyst may include unilateral pelvic pain or dyspareunia. Complications can include hemorrhage, rupture, or torsion. Diagnosis may occur after a thorough history and physical examination. In addition, clinicians may use ultrasound for confirmation. Many follicular cysts can spontaneously resolve within three months. Birth control pills can be prescribed to regulate the menstrual cycle and prevent hormonal disruption. Depending on the clinical presentation and characteristics of the cyst, surgical resection of the cyst may be required.

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Related links

Anatomy of the female reproductive organs of the pelvis
Ovarian cyst
Ovarian cysts and tumors: Pathology review

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