Department of Urology, St. Michael's Hospital, University of Toronto, Toronto, Canada.
Urology. 2010 Aug;76(2):295-300. doi: 10.1016/j.urology.2009.12.015. Epub 2010 Mar 5.
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.
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.
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.
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.
评估 CT（计算机断层扫描）和 US（超声）在结石测量方面的差异。轴向增强螺旋 CT 是评估尿路结石的参考标准成像方式；然而，US 也常被使用。这两种技术在结石测量方面的差异描述较差，测量误差的原因仍不清楚。
回顾 2004 年 6 月以来，我院所有在不到 1 个月内同时接受腹部 CT 和肾脏 US 的患者。所有病例均在 CT 和 US 上均发现孤立性肾结石。
我们共发现 60 例患者的 71 个结石。与 CT 相比，US 高估了结石大小，这种影响在较小的结石中更为明显。CT 上的平均结石测量值为 7.4 +/- 4.4 毫米，US 上为 9.2 +/- 4.5 毫米（P =.018）。对于 </=5 毫米的结石，US 测量值比 CT 测量值平均大 1.9 +/- 1.2 毫米（P <.001）。60%的 </=5 毫米结石的 US 和 CT 测量值不一致。不一致与 US 测量的皮肤至结石距离有关（P =.018），但与体重指数无关（P =.189）或结石在尿路中的位置无关（P =.161）。对文献的回顾表明，US 检测输尿管结石的敏感性和特异性分别为 45%和 94%，检测肾结石的敏感性和特异性分别为 45%和 88%。
US 在尿石症中高估了结石大小，这一发现可能对结石管理有影响。结石测量的不一致性随大小而变化，在 </=5 毫米的结石中最大。US 测量皮肤至结石距离是 US 测量肾结石误差的重要决定因素。
