An ovarian cyst is a fluid-filled sac that can form on or inside an organ. A physiologic cyst, also known as a functional cyst, is a temporary outcome of a healthy menstrual cycle. Unlike cysts caused by disease or abnormal cell growth, these cysts are a sign that the ovaries are carrying out their typical hormone production and egg-releasing functions. They are typically benign, self-limiting, and resolve on their own without the need for medical intervention.
The Function Behind the Formation
The term “physiologic” means these cysts arise from the body’s normal processes, specifically the hormonal changes that regulate the menstrual cycle. Each month, the ovaries prepare to release an egg, and this process involves the growth and transformation of structures known as follicles. These cysts occur when the normal sequence of events during the cycle is slightly interrupted, leading to the temporary accumulation of fluid. Because these cysts are directly tied to the reproductive cycle, they are most common in women who are still having regular periods. They are often asymptomatic and frequently discovered incidentally during a routine pelvic ultrasound.
The Two Types of Physiologic Cysts
The two main types of physiologic ovarian cysts are follicular cysts and corpus luteum cysts, distinguished by the phase of the menstrual cycle in which they form. Both are common and result from minor deviations in the ovulation process. Understanding their formation helps clarify why they are considered functional.
Follicular Cysts
Follicular cysts develop during the first half of the menstrual cycle, known as the follicular phase. Normally, a fluid-filled sac called a follicle houses a developing egg and produces the hormone estrogen. At mid-cycle, the follicle typically ruptures to release the mature egg, a process called ovulation. A follicular cyst forms if the dominant follicle fails to rupture and instead continues to grow, filling with fluid. These cysts are the most common type of physiologic cyst and often resolve quite quickly.
Corpus Luteum Cysts
Corpus luteum cysts form after ovulation, during the second half of the cycle. Once the egg is released, the remaining follicle transforms into a structure called the corpus luteum, which produces progesterone and estrogen to prepare the uterus for a potential pregnancy. A corpus luteum cyst develops if the opening where the egg was released seals up, causing fluid or occasionally blood to accumulate inside the sac. These cysts may contain a small amount of blood and can sometimes cause more noticeable symptoms, such as pain, than follicular cysts. If they bleed significantly, they may be referred to as hemorrhagic corpus luteum cysts.
Identifying and Monitoring Physiologic Cysts
Physiologic cysts often cause no symptoms, but when they do, they may lead to mild pelvic pain, a feeling of fullness, or pressure in the lower abdomen. The presence of a cyst is typically identified incidentally during a pelvic ultrasound, which is the primary imaging tool used for evaluation. Transvaginal ultrasonography allows medical professionals to assess the size, shape, and internal characteristics of the cyst, which helps determine its nature. For cysts that appear simple and meet the criteria for physiologic cysts, the standard management approach is “watchful waiting” or expectant management. Most physiologic cysts disappear spontaneously within one to three menstrual cycles (about four to twelve weeks), and follow-up ultrasounds are often scheduled to confirm the cyst’s resolution.
Distinguishing Physiologic from Pathological Cysts
The distinction between a temporary physiologic cyst and a pathological cyst (a structure resulting from abnormal cell growth) is based on key characteristics. Physiologic cysts are simple, thin-walled, fluid-filled, and self-limiting, resolving within a few months. Pathological cysts, such as dermoid cysts or endometriomas, often have complex features like solid areas or multiple internal compartments, and tend to persist or grow over time. Cysts larger than 5 to 10 centimeters, or those that persist beyond two to three menstrual cycles, usually require closer monitoring or further investigation. Sudden, severe pelvic pain accompanied by nausea, vomiting, or signs of shock requires immediate medical attention, as these acute symptoms could indicate cyst rupture or ovarian torsion.