What indicates the presence of renal stones in an ultrasound examination?

The presence of renal stones during an ultrasound examination is indicated by posterior acoustic shadowing. This phenomenon occurs when sound waves encounter a highly reflective surface, which is characteristic of solid structures like stones. When the ultrasound beam passes through the renal tissue and hits the stone, it does not transmit through the dense material, resulting in a shadow that extends behind the stone. This acoustic shadowing serves as a clear indicator that a calcified structure is present in the renal system.

In contrast, increased renal echogenicity typically suggests issues such as renal parenchymal disease or fat deposition, but it does not specifically signify the presence of stones. Hydronephrosis refers to the swelling of a kidney due to a backup of urine, which can occur for various reasons, including obstructive processes caused by stones, but is not exclusive to them. Cystic renal alterations, such as simple cysts, do not indicate renal stones and can appear as fluid-filled spaces that are clearly distinguishable from solid masses like stones.

Thus, the presence of posterior acoustic shadowing is the most specific indicator of renal stones on ultrasound examinations.