What is the primary characteristic of an anechoic structure in medical imaging?

Anechoic structures in medical imaging are characterized by their ability to transmit sound waves without reflecting them back. This quality typically indicates the presence of fluid. In the context of ultrasound imaging, anechoic areas appear dark because fluid does not create echoes; thus, they are often used to identify collections of fluids such as cysts or the urinary bladder. When a structure appears anechoic, it suggests that it is filled with a homogeneous liquid, distinguishing it from solid or vascularized tissues that produce varying degrees of echogenicity and reflect sound waves differently. Understanding this characteristic is crucial for accurate diagnosis and assessment in medical imaging.