Assessment of accuracy of ultrasound in detection and size estimation of kidney stones

Abstract

 Introduction: Ultrasound is the first line investigation for diagnosis of kidney stones, as it is readily available, inexpensive and radiation free. However, computed tomography (CT) scan is considered as the gold standard imaging modality for detection of urolithiasis. The objective of this study was to  assess the accuracy of ultrasound in detection and size estimation of kidney stones in comparison to CT scan.

Materials and Methods: In this prospective observational study, kidney stone patients, who had undergone ultrasonography and CT scan within two weeks of interval were included. The demographic parameters, stone size, stone side and location were noted. The sensitivity and size accuracy of ultrasound was determined using CT scan as the standard.

Results: Total of 173 patients of kidney stones having ultrasound and CT reports were analyzed. The average age was 39.94±15.1 years. The overall sensitivity of ultrasound in detecting renal stones was 82.1%. The sensitivity of ultrasound increased significantly (p<0.001) with the increase in size of stones. The ultrasound significantly underestimated the stones >20mm (p<0.001), however, it overestimated the stones <20mm, although statistically insignificant. When ultrasound was used alone in renal stones, an average of 15% of patients could be inappropriately counselled for management, and this was greatest in the stone size group 5-10mm (45.1%).

Conclusions: Ultrasound has lower sensitivity for smaller stones and lower accuracy for larger stones than CT scan. When used alone for renal stones, ultrasound may lead to inappropriate counselling and a change in treatment recommendation in one in seven patients.