The role of ultrasonography in detecting urinary tract calculi compared to CT scan

Abstract

Objective: To evaluate the accuracy of ultrasonography (US) in measuring the urinary tract stone using non-contrast computed tomography (NCCT) as the standard reference.

Patients and methods: A total of 184 patients suspected with urolithiasis who had undergone NCCT and US radiologic investigation from 2015 to 2017 were enrolled in this study. The sensitivity, specificity, and stone size measured in US were validated by NCCT. Data of the stone size in US were classified into four groups (0-3.5, 3.6-5, 5.1-10, >10 mm) and then compared with NCCT data.

Results: In 184 patients, NCCT detected 276 (97.2%) stones, while US could identify 213 (75.5%) stones. Overall sensitivity and specificity of US were 75.4% and 16.7%, respectively. Detection rate of mid and distal ureteral stone was lower than that at other locations. The detection rate increased with the stone size. About 73% concordance was obtained for the stone size measured by US and NCCT (Pearson's correlation coefficient was 0.841). Factors such as the stone size, amount of hydronephrosis, and weight affected the detection rate of the urinary tract stone using US (P<0.001, P=0.02, and P=0.01, respectively).

Conclusion: The stone size obtained by US was almost the same as that detected by NCCT; however, US is a limited imaging modality in detecting urinary tract stone, especially when used by an inexperienced radiologist, and in the case of smaller stone size, increased weight, and low grade of hydronephrosis.

Keywords: non-contrast computed tomography; stone; ultrasonography; urinary tract.

Figure 1

The Bland–Altman plots from US and NCCT limits of agreement for the stone size were between −5.659 and 5.745 and the mean difference (95% CI) was 0.043 (0.346–0.432). Notes: The spread around the mean for the stone size showed variations across all levels, and only a few participants fell outside the limit of agreement. The mean difference was not associated with the means of the two methods, confirming the acceptable level of agreement. Abbreviations: NCCT, non-contrast enhanced computed tomography; US, ultrasonography.