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Urology. 2010 Aug;76(2):295-300. doi: 10.1016/j.urology.2009.12.015. Epub 2010 Mar 5.

Limitations to ultrasound in the detection and measurement of urinary tract calculi.

Author information

1
Department of Urology, St. Michael's Hospital, University of Toronto, Toronto, Canada.

Abstract

OBJECTIVES:

To evaluate differences in stone measurement using computed tomography (CT) and ultrasound (US). Axial unenhanced helical CT is the reference-standard imaging modality for the assessment of urinary tract calculi; however, US is also commonly used. Differences in stone measurement using these techniques are poorly described and contributors to measurement error remain unknown.

METHODS:

All patients at our institution undergoing both abdominal CT and renal US less than 1 month apart since June 2004 were reviewed. Solitary renal calculi were identified on both CT and US in all cases.

RESULTS:

We identified 71 calculi in 60 patients. Compared with CT, US overestimated stone size, an effect that was more pronounced with smaller calculi. The mean stone measurement on CT was 7.4 +/- 4.4 mm and on US it was 9.2 +/- 4.5 mm (P = .018). For stones </=5 mm, US measurements were a mean of 1.9 +/- 1.2 mm greater than CT (P <.001). US and CT measurements were discordant for 60% of stones </=5 mm. Discordance was associated with US measurement of skin-to-stone distance (P = .018), but not body mass index (P = .189) or location within the urinary tract (P = .161). Review of the literature revealed that US has a pooled sensitivity and specificity of 45% and 94%, respectively, for the detection of ureteric calculi and 45% and 88%, respectively, for renal calculi.

CONCLUSIONS:

US overestimates stone size in urolithiasis, a finding that may have implications for stone management. Discordance in stone measurement varies with size and is greatest in stones </=5 mm. US measurement of skin-stone-distance is an important determinant of error in US measurement of renal calculi.

PMID:
20206970
DOI:
10.1016/j.urology.2009.12.015
[Indexed for MEDLINE]

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