Ultrasound May Often Overestimate Renal Stone Size

Especially true for smaller stones; CT may measure stone size more accurately in urolithiasis

THURSDAY, Aug. 19 (HealthDay News) -- Ultrasound often overestimates the size of stones in urolithiasis, particularly when the stones are 5 mm or smaller, according to research published in the August issue of Urology.

A. Andrew Ray, of the University of Toronto, and colleagues reviewed the results of computed tomography (CT) and renal ultrasound in 60 patients (who underwent both) to compare differences in stone measurement between the two approaches. Solitary renal calculi were identified with both approaches in all cases.

The researchers found 71 calculi in the subjects, and discovered that ultrasound overestimated stone size compared with CT, especially with smaller calculi; mean stone measurement by CT was 7.4 mm, compared with 9.2 mm for ultrasound. Ultrasound measurements were a mean 1.9 mm greater than CT for stones that were 5 mm or smaller Discordance was found between the two methods in 60 percent of stones 5 mm or less, and was associated with ultrasound measurement of skin-to-stone distance.

"Our data indicate that ultrasound overestimates renal stone size, an effect that is particularly pronounced for stones ≤5 mm. Furthermore, compared with unenhanced CT, ultrasound has poor sensitivity for detecting stones in both the ureter and kidney. For these reasons, ultrasound should be considered of limited value in the work-up of urolithiasis. Management decisions should incorporate information from other imaging modalities such as KUB [kidney, ureter, and bladder] and axial CT," the authors conclude.

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