How do renal cysts typically appear on ultrasound?

Renal cysts typically appear on ultrasound as well-defined, anechoic structures with posterior acoustic enhancement. This characteristic appearance is due to the fluid content of the cyst, which transmits ultrasound waves easily, appearing dark (anechoic) on the image. The well-defined borders help in distinguishing these cysts from solid masses, which often have irregular contours and can be echogenic due to internal structures or calcifications.

Posterior acoustic enhancement occurs because the sound waves travel through the fluid in the cyst without significant attenuation. As a result, the area directly behind the cyst will appear brighter compared to adjacent tissues, enhancing the visualization of the lesion. This is an important diagnostic feature that aids in identifying simple renal cysts as opposed to more complex lesions that may require further evaluation.

Other options depict characteristics that are not typical of uncomplicated renal cysts. For example, solid, echogenic masses with irregular borders suggest the presence of a solid tumor or more complex renal pathology. Hypoechoic shadowing lesions usually indicate some degree of internal structure or solid tissue, which is not consistent with simple cysts. Large cystic areas with calcifications suggest a more complicated cystic process, potentially indicating chronicity or infection.