From the Guidelines
Follicles and cysts are distinct structures in the ovaries, with follicles being normal and essential for reproduction, and cysts being abnormal fluid-filled sacs that may cause symptoms if they grow large enough. The key difference between follicles and cysts lies in their origin, function, and potential impact on health. Follicles are a natural part of the menstrual cycle, containing developing eggs and typically measuring 2-10mm in size, with the dominant follicle growing to about 20-25mm before ovulation 1. In contrast, cysts are abnormal growths that can develop when a follicle fails to release its egg or doesn't dissolve properly after ovulation.
According to the O-RADS US Risk Stratification and Management System, follicles are considered part of the physiologic category, consistent with normal ovarian physiology, whereas cysts are categorized based on their characteristics, such as simple cysts, corpus luteum, or lesions with solid components 1. The American College of Radiology's guidelines also emphasize the importance of distinguishing between benign and potentially malignant adnexal masses, with simple cysts, regardless of size and menopausal status, not being associated with an increased risk of cancer 1.
Some key points to consider when differentiating between follicles and cysts include:
- Follicles are temporary structures that develop and regress during each menstrual cycle, whereas cysts can persist for longer periods.
- Most small cysts resolve spontaneously within 1-3 menstrual cycles without treatment, but larger or symptomatic cysts may require monitoring or surgical intervention.
- The risk of malignancy in benign-appearing lesions on US managed conservatively is low, with a recent study demonstrating a risk of malignancy of < 1% in a cohort of 970 average-risk women 1.
- Unilocular cysts in the premenopausal population have a very low risk of malignancy, with a recent meta-analysis demonstrating a risk of malignancy of 0.6% in 987 unilocular cysts removed surgically in premenopausal women 1.
In clinical practice, it is essential to accurately diagnose and manage adnexal masses, with a focus on minimizing the risk of malignancy and optimizing patient outcomes, particularly in terms of morbidity, mortality, and quality of life 1.
From the Research
Definition of Follicles and Cysts
- Follicles are small, fluid-filled structures in the ovaries that contain eggs 2.
- Cysts, on the other hand, are abnormal, fluid-filled sacs that can form in the ovaries [no direct evidence available].
Formation of Follicles
- Follicles form from primordial germ cells, which migrate to the ovaries during embryonic development and proliferate to form germ cell nests 2.
- These nests eventually break down to generate primordial follicles, each containing an oocyte surrounded by a layer of somatic pre-granulosa cells 2.
Difference between Follicles and Cysts
- Follicles are a normal part of ovarian function, while cysts are abnormal and can be caused by a variety of factors [no direct evidence available].
- Follicles contain eggs and are involved in the reproductive cycle, while cysts do not contain eggs and are not involved in reproduction 2.