What findings on ultrasound suggest kidney stones?

Echogenic foci with posterior acoustic shadowing are classic ultrasound findings that indicate the presence of kidney stones, also known as renal calculi. The stones are typically denser than the surrounding tissues due to their mineral composition, which results in the echogenic appearance on ultrasound. When sound waves encounter these dense structures, they cannot pass through the stones effectively, leading to the production of posterior acoustic shadowing. This shadowing reflects the obstruction of sound waves behind the stone, which provides strong evidence of its presence.

Other findings such as hypoechoic masses without shadowing, fluid-filled areas without echogenicity, or large cystic structures with smooth borders typically do not represent kidney stones. Hypoechoic masses could indicate other conditions like tumors or abscesses, and fluid-filled areas or cystic structures would suggest conditions like renal cysts rather than stones. Thus, the described echogenic foci with posterior acoustic shadowing is a hallmark for detecting kidney stones in ultrasound imaging.