Subtle hyperechoic foci in both kidneys, probably renal calculi. left renal cyst measured 17mm. there is no hydronephrosis or other masses. what does this kidney ultrasound mean?

Exactly what you say: The ultrasound is what it is, the clinical significance must be determined by the treating physician with multiple associated factors to be taken into consideration.

no cancer: Renal cysts are very common and nothing to worry about. The subtle hyperechoic foci probably represent tiny kidney stones which may grow over time. No hydronephrosis means no evidence of something obstructing the flow of urine to your bladder. No masses means just that. Please see your doctor to review this report as well as current laboratory tests of your kidney function.

Probably fine: No hydronephrosis and no masses is normal, so these are both good. Renal cysts are very common and usually benign (ask if they are simple cysts). Small hyperechoic foci sounds like small kidney stones, but these do not cause pain unless you are passing one (would have hydronephrosis). A noncontrast ct scan is best to evaluate kidney stones but does involve radiation. See a urologist.

Here are some ...: Most likely, all the described finding in renal ultrasound is not clinically significant. Also, remember: despite all medical advance, today's medical care is still based on indirect evidence resulting from continual collection & analysis of available experiences so to make a reasonable sound decision for reasonable action.