An ovarian cyst is a fluid-filled sac that develops on or within an ovary. Most of these masses are benign, often arising as a normal part of the menstrual cycle, but some are complex and require closer attention. Healthcare providers rely on ultrasound examination to determine the nature of a cyst—whether it is a simple, functional structure or a complex mass. This non-invasive imaging technique, typically performed using transvaginal or transabdominal probes, is the primary method for visualizing the ovary and characterizing the mass’s physical features. The visual details captured by the ultrasound are used to classify the cyst and guide patient care.
Interpreting the Ovarian Ultrasound Image
The visual language used in ultrasound reports centers on echogenicity, which describes how bright or dark an area appears based on how the tissue reflects sound waves. A purely fluid-filled structure, such as a simple cyst, is described as anechoic, meaning it appears black because it does not reflect sound waves.
Tissues or fluids that reflect sound waves appear in shades of gray to white, referred to as hypoechoic (dark gray) or echogenic (bright white). Bright echoes often indicate solid components, thick fluid, or fat within the mass. Other structural features include septations, which are internal walls that divide the cyst into multiple compartments.
A mural nodule is a solid projection arising from the inner wall of the cyst, and its presence can be concerning. Sonographers employ Color Doppler imaging to map blood flow and assess risk. Demonstrating blood flow within a solid component or septations indicates active cellular growth, a significant finding in mass evaluation.
Visual Characteristics of Simple Ovarian Cysts
The most common types of ovarian cysts are functional cysts, which include follicular and corpus luteum cysts that develop during the normal ovulatory cycle. The classic ultrasound appearance of these benign cysts is distinct. A simple cyst is defined by being purely anechoic, appearing as a perfectly black, spherical structure with smooth, thin walls.
These cysts are typically unilocular, meaning they consist of a single fluid-filled compartment without any internal divisions or septations. They lack internal solid components, debris, or blood flow when examined with Color Doppler imaging. This uniform, fluid-filled appearance is strongly associated with a benign nature, showing a near-zero rate of malignancy for cysts that meet these criteria.
Size remains a factor in clinical management, even for masses with benign features. Cysts up to 10 centimeters in diameter are overwhelmingly likely to be benign in both pre- and post-menopausal women. For smaller cysts, particularly those under 5 centimeters, follow-up imaging may not be required, as they are expected to resolve spontaneously within a few menstrual cycles.
Distinct Ultrasound Features of Complex Cysts
A cyst is considered complex if it deviates from the simple, anechoic, and unilocular criteria, often containing solid components, thick walls, or internal echoes. This heterogeneity can be due to various benign conditions but also raises the possibility of malignancy. The specific internal texture and features of a complex cyst often point toward a definitive diagnosis.
Endometrioma
The endometrioma is a common complex mass filled with old blood associated with endometriosis. On ultrasound, these masses typically display diffuse, homogeneous low-level echoes, often described as having a characteristic “ground-glass” appearance. This visual texture is caused by the thick, proteinaceous, hemorrhagic fluid within the cyst.
Dermoid Cyst (Mature Cystic Teratoma)
The dermoid cyst, or mature cystic teratoma, is comprised of various tissues like hair, fat, and bone. These cysts are characterized by highly echogenic (bright) components due to the presence of fat or calcification. A classic finding is the “Rokitansky nodule” or “dermoid plug,” a brightly reflective projection that may create a sharp shadow known as the “tip-of-the-iceberg” sign.
Hemorrhagic Cysts
Hemorrhagic cysts are functional cysts that have experienced bleeding, and their appearance changes depending on the age of the clot. Acutely, they can display a complex cystic pattern with fine, intersecting lines called a reticular pattern, representing fibrin strands within the blood. A large blood clot can mimic a solid area, but it typically has straight or concave margins and lacks internal blood flow, distinguishing it from a true solid tumor.
Features that raise concern for malignancy include thick, irregular septations, a large solid component, or multiple mural nodules. The most suspicious feature is the detection of prominent, active blood flow within the solid components or septations when Color Doppler is applied. A large complex mass demonstrating high vascularity is prioritized for further evaluation.
How Ultrasound Appearance Guides Next Steps
The specific visual characteristics of an ovarian cyst determine the subsequent management plan, ranging from observation to intervention. For masses that are small and simple—anechoic, thin-walled, and unilocular—the approach is watchful waiting. A follow-up ultrasound is scheduled to confirm spontaneous resolution, as these are highly likely to be functional structures that disappear on their own.
Cysts with complex features, such as those consistent with a hemorrhagic cyst or endometrioma, are often managed with a short-term follow-up scan, typically in 6 to 12 weeks. If the mass persists, grows, or displays suspicious traits like enlarged solid parts or increased vascularity, further testing is warranted. This may include blood work for tumor markers or referral for surgical evaluation to definitively diagnose the mass.