An endometrioma is a specific type of ovarian cyst that forms when tissue similar to the lining of the uterus (endometrium) grows on the ovary. This misplaced tissue responds to cyclical hormonal changes, causing monthly bleeding within the ovary that has no exit. The resulting accumulation of thick, dark brown blood gives these cysts their common name: “chocolate cysts.” The rate at which these cysts change size is highly individualized and rarely predictable.
Defining Endometriomas and Their Measurement
Endometriomas are cystic structures most often found on the ovaries, varying significantly in size from small lesions up to 20 centimeters in diameter. The fluid inside is composed of degenerated blood products from repeated cyclical hemorrhage, creating the characteristic thick, dark filling.
Clinicians primarily rely on transvaginal ultrasound to track the progression of an endometrioma. On ultrasound, these cysts typically display a distinct “ground-glass” appearance, consistent with old hemorrhagic debris. This technique allows medical professionals to accurately measure the cyst’s size, usually by recording the mean diameter or calculating its volume.
Monitoring the size and characteristics of the cyst over time is standard practice, often involving repeat scans spaced several months apart. This systematic measurement allows for the identification of any significant change in size or appearance. Although transvaginal ultrasound is the primary tool, magnetic resonance imaging (MRI) may be used in complex cases to gain a clearer picture of the cyst’s structure and surrounding anatomy.
Observed Patterns of Growth
The growth of an endometrioma is typically not a continuous or linear process, exhibiting a highly variable pattern of progression. Observational studies tracking cysts over time reveal that a significant number of endometriomas either remain stable or reduce in size on their own. One study demonstrated that approximately 31% of cysts showed no meaningful change, while 47% experienced an overall reduction in diameter when managed expectantly.
Conversely, only a smaller proportion of cysts (about 22% in the same study) increased in size during the follow-up period. The median annual change observed across all patients suggests a slight tendency toward regression, noted at around -1.7 millimeters per year. This overall trend highlights that for many, the cyst volume stabilizes or slowly decreases.
The concept of “rapid growth” is usually defined by a notable increase in size over a short follow-up period, such as an increase in diameter greater than 10 millimeters in six months. While some studies suggest an average growth rate of approximately 0.5 centimeters per six months for those that enlarge, significant, exponential growth is considered unusual. Any increase in size, especially if accompanied by changes in the cyst’s internal features, warrants prompt re-evaluation.
The dynamic nature of these cysts means that a measurement taken at one point does not reliably predict the size at a later date. This variability makes long-term monitoring, rather than immediate intervention, the preferred approach for many asymptomatic cases. The specific trajectory of size change is unique to the individual and often linked to underlying hormonal fluctuations.
Factors That Influence Growth Rate
The primary driver of endometrioma growth is the body’s hormonal environment, as the tissue within the cyst is estrogen-dependent. This ectopic tissue responds to the cyclical peaks and troughs of estrogen produced during the menstrual cycle. This cyclical response causes internal bleeding and subsequent enlargement of the cyst.
Periods of high, sustained estrogen exposure can accelerate this growth. For instance, women undergoing ovarian stimulation for assisted reproductive techniques (such as in vitro fertilization) may see an increase in cyst volume. Studies show that a majority of endometriomas, sometimes up to 82%, grow during these cycles, though the absolute increase is typically small and transient.
The initial size of the cyst can influence its future growth potential, with larger cysts sometimes showing a greater tendency to enlarge during hormonal stimulation. Conversely, conditions that suppress ovarian function or estrogen production can lead to stabilization or regression. Pregnancy (which creates a high-progesterone, low-cyclical-estrogen state) and the onset of menopause often result in the shrinkage of endometriomas.
Medical treatments that inhibit ovulation or suppress the hormonal cycle are designed to interrupt the monthly bleeding cycle within the cyst. By limiting the influx of blood and cellular debris, these treatments can help reduce the cyst size or prevent further growth. This demonstrates the direct link between hormonal signaling and the growth trajectory of these lesions.
Why Monitoring Growth Matters
Tracking the growth rate of an endometrioma is a fundamental part of patient management because the rate and pattern of change have clinical implications. One concern is the small risk of malignant transformation, where the cyst develops into a type of ovarian cancer, most commonly clear cell or endometrioid carcinoma. While rare, an increase in size, the presence of solid components, or a change in the cyst’s internal appearance can signal the need for further investigation to rule out malignancy.
Monitoring is important for assessing the risk of acute complications that require immediate attention. Endometriomas larger than six centimeters in diameter carry an increased risk of ovarian torsion, a medical emergency involving the twisting of the ovary on its supporting ligaments. Rupture of a large endometrioma is another complication that can cause severe, sudden abdominal pain as the contents spill into the pelvic cavity.
The growth rate and ultimate size of the cyst inform treatment decisions, particularly concerning fertility preservation. Large or rapidly growing endometriomas may necessitate surgical removal, but surgery carries a risk of damaging healthy ovarian tissue, which can reduce the ovarian reserve. Therefore, monitoring helps determine the optimal time for intervention, weighing the risk of cyst progression against the potential harm of a procedure.