Ovarian cysts are common, typically benign, fluid-filled sacs that develop on or within an ovary, often forming as a normal part of the menstrual cycle. Ultrasound imaging is the primary tool for initial detection and characterization, providing a detailed visual assessment of the cyst’s structure and contents. Analyzing how sound waves interact with the tissue allows healthcare providers to determine if a cyst appears simple or complex. This visual information guides decisions regarding monitoring or further evaluation.
Understanding Ultrasound Terminology
Reading an ultrasound report requires understanding specific terms describing how tissues reflect sound waves. Echogenicity refers to the brightness of a structure on the screen, determined by the amount of sound waves reflected back to the probe.
Anechoic structures appear completely black because they reflect no sound waves, which is characteristic of simple clear fluid. Conversely, hyperechoic structures appear bright or white, often indicating dense tissue, fat, or calcification. Areas that are darker than the surrounding tissue but not entirely black are hypoechoic, suggesting they are less dense, such as some solid tumors or thick fluid. The term mixed echogenicity indicates that a mass contains both fluid and solid components, appearing as a mix of black, gray, and white areas.
Other descriptive terms detail the cyst’s architecture. Septations are internal walls or dividing lines within the cyst, which can be described as thin or thick. Posterior acoustic enhancement is a common finding in fluid-filled cysts. This occurs where the area immediately behind the cyst appears brighter than the surrounding tissue because sound waves passed easily through the fluid.
Visual Characteristics of Simple Cysts
Simple cysts are the most common type encountered, often representing functional cysts related to the menstrual cycle, such as follicular cysts. The defining feature of a simple cyst on ultrasound is its uniform appearance, which suggests a harmless, fluid-only content. The interior of these cysts is almost perfectly anechoic, meaning the fluid inside is clear and appears black on the screen.
These cysts are typically unilocular, meaning they have a single chamber with no internal divisions or septations. The outer wall is characteristically smooth, thin, and well-defined, often appearing almost imperceptible on the image. Due to the clear fluid contents, simple cysts nearly always exhibit posterior acoustic enhancement, which is a helpful indicator of their benign, fluid-filled nature. Simple cysts do not contain solid components or show internal blood flow when assessed with color Doppler imaging.
Identifying Complex and Atypical Cysts
A cyst is classified as complex when it displays features beyond the simple, anechoic, unilocular structure. This complexity suggests the presence of blood, debris, or solid tissue. The visual differentiation of these features guides the need for follow-up imaging or further diagnostic steps.
Hemorrhagic Cysts
One common complex appearance is a hemorrhagic cyst, which results from bleeding into a functional cyst. These cysts often show fine, web-like strands of fibrin within the fluid, sometimes described as a “spider web” or “fishnet pattern.” These strands are internal echoes resulting from clotting blood.
Endometriomas and Dermoids
Endometriomas, often called “chocolate cysts,” appear with homogeneous, low-level internal echogenicity. This gives them a characteristic “ground-glass” appearance due to the old, thick blood they contain. Dermoid cysts contain fat, hair, and other dense tissues, displaying highly hyperechoic areas with strong acoustic shadowing. Acoustic shadowing is a phenomenon where dense material completely blocks the sound waves, creating a dark shadow behind it.
Architectural Features
Complex cysts may also contain septations that are noticeably thick or irregular. They may also present with solid-looking projections, called mural nodules, extending into the cavity. The presence of internal blood flow within any solid-appearing part of the cyst, detected with color Doppler, is another visual feature that classifies a cyst as complex and warrants closer evaluation.