An ovarian cyst is a fluid-filled sac that develops on or within an ovary, and these are extremely common findings, particularly in people who are still menstruating. Many go unnoticed unless found incidentally during a routine pelvic exam or imaging procedure. A pelvic ultrasound is the primary non-invasive method for detecting and characterizing these structures. This diagnostic tool provides immediate, detailed images that allow healthcare providers to determine the cyst’s size, location, and internal makeup, which guides the necessary next steps.
How Ultrasound Visualizes Ovarian Structures
Ultrasound technology works by emitting high-frequency sound waves into the pelvic area, which bounce back when they hit different tissues and are then translated into a visual image. The way a tissue reflects sound determines its appearance on the screen, a property called echogenicity. Fluid-filled structures, like simple cysts, do not reflect sound waves and appear perfectly black; this is described as anechoic.
Conversely, dense or solid tissues, such as muscle or tumors, reflect sound strongly, appearing bright white or gray and are described as echogenic or hyperechoic. The ultrasound beam often passes through fluid unimpeded, resulting in a brighter area just behind the cyst, known as posterior acoustic enhancement. This enhancement is a classic indicator that the structure is purely fluid-filled.
To obtain the clearest images of the ovaries, a transvaginal approach is typically used, where a small probe is inserted into the vagina, placing it closer to the pelvic organs. This proximity provides higher-resolution images than the abdominal approach, which is necessary for accurately assessing the fine details of a cyst’s walls and contents.
Appearance of Simple and Functional Cysts
The majority of ovarian cysts are classified as simple or functional, meaning they are a normal result of the menstrual cycle and are almost always benign. On ultrasound, a simple cyst appears as a smooth, perfectly round or oval structure with very thin, well-defined walls. Its interior is completely anechoic (black), indicating it is filled only with clear fluid and contains no internal solid components or dividing walls.
Functional cysts, such as follicular cysts and corpus luteum cysts, are common types of simple cysts that develop when the monthly ovulation process goes slightly awry. A follicular cyst forms when the follicle fails to rupture and release the egg, continuing instead to grow into a thin-walled, fluid-filled sac. A corpus luteum cyst forms after an egg is released, and the remaining structure seals itself off, sometimes accumulating fluid or blood.
A corpus luteum cyst may look slightly more complex due to internal bleeding, sometimes displaying a “ring of fire” pattern on Doppler ultrasound due to prominent blood flow in its wall. However, the internal appearance of a functional cyst, even with some low-level echoes from blood products, typically remains unilocular, meaning it has only one chamber. These cysts are typically self-resolving, often disappearing within a few menstrual cycles.
Key Image Features of Complex Cysts
A cyst is classified as complex when its ultrasound appearance includes features beyond a simple, fluid-filled sac. One key feature is the presence of internal septations, which are thin strands or dividing walls that cross the interior of the cyst, creating multiple chambers. The thickness and irregularity of these septations are important details, as thick or nodular septa raise more concern than thin, fine lines.
Another significant finding is a solid component, which appears as an echogenic area within the anechoic fluid, suggesting the presence of tissue rather than just liquid. When this solid area protrudes from the inner wall into the cyst cavity, it is termed a papillary projection. Ultrasound technology using Doppler can check for internal vascularity (blood flow) within these solid components or projections.
The presence of blood flow within a solid area increases the level of concern and may require further imaging or biopsy. Certain benign complex cysts have characteristic appearances. An endometrioma, which contains old blood, often displays homogeneous low-level echoes, giving it a characteristic “ground-glass” appearance. Another example is a dermoid cyst, which contains hair, fat, or other dense tissues, appearing highly echogenic with noticeable shadowing.
Interpreting Findings and Management
The interpretation of ultrasound findings involves a specialist, typically a radiologist, who documents the visual characteristics of the cyst, including its size, wall features, and internal components. This detailed report is then used by the treating physician to classify the cyst’s level of concern, often utilizing standardized risk stratification systems. These systems help the clinician determine the probability of the cyst being benign versus having a potential for malignancy.
The management plan is determined by this classification and generally falls into three categories. For cysts displaying purely simple characteristics, the recommendation is often watchful waiting with a follow-up ultrasound in several months to confirm spontaneous resolution or stability. This is based on the high likelihood that the cyst is functional and temporary.
If the cyst is complex but displays features typical of a common benign type, such as an endometrioma or dermoid, the management may involve expectant monitoring or surgical removal if it is large or causing symptoms. Cysts with highly concerning features, such as prominent solid components with blood flow or thick, irregular walls, may be referred for surgical removal and definitive pathological analysis.