Which radiological feature is indicative of a simple liver cyst?

A simple liver cyst is characterized by its anechoic appearance, meaning it appears completely dark on ultrasound due to the fluid content within it. This lack of internal echoes distinguishes it from other lesions. Additionally, a simple liver cyst has a smooth border, which contributes to its clear definition on imaging. This well-defined, smooth boundary confirms that the structure is benign and non-complex.

In contrast, other features do not correspond with a simple liver cyst. For instance, heterogeneous echogenicity suggests a mixture of different tissue types or components, which implies a more complex pathological process rather than a simple fluid-filled cyst. A hyperechoic halo could indicate the presence of surrounding edema or inflammation, which is not a typical characteristic of a simple cyst. Lastly, complex multi-septated structures suggest the presence of multiple compartments or divisions within a cyst, indicating a more complicated entity (such as a complex cyst or tumor) rather than a straightforward, simple cyst.

Thus, the presence of an anechoic appearance with smooth borders is definitive for identifying a simple liver cyst on ultrasound.