The relationship between hydronephrosis severity on ultrasound and kidney stone size


Kidney stones are a common urologic condition, with an increasing incidence and prevalence globally. Non-contrast computed tomography (CT) is frequently used in emergency departments to evaluate suspected kidney stones, given its high accuracy for detecting the presence, size and location of stones. However, ultrasound is advantageous due to lower cost, lack of ionizing radiation, and wider availability. Prior studies have shown emergency physicians can accurately detect hydronephrosis on renal ultrasound, but the correlation with stone size is unknown. Since stones <5mm are more likely to pass spontaneously while those >5mm often require intervention, stone size is an important prognostic factor.

Main Body

Goertz et al. performed a retrospective study of adult emergency department patients who had a renal ultrasound for suspected kidney stones followed by a confirming CT scan. The severity of hydronephrosis on ultrasound was defined as none, mild, moderate or severe based on standardized criteria. Of the 177 patients, 72.9% had no or mild hydronephrosis on ultrasound, while 27.1% had moderate or severe hydronephrosis. Only 12.4% of the no/mild hydronephrosis group had stones >5mm on CT compared to 35.4% of the moderate/severe hydronephrosis group. Test characteristics showed reasonable specificity (78.5%) and high negative predictive value (87.6%) for no/mild hydronephrosis to detect stones ≤5mm.

This study found increasing hydronephrosis severity on point-of-care renal ultrasound correlated with a greater likelihood of larger kidney stones on subsequent CT imaging. Ultrasound evidence of no or mild hydronephrosis makes larger obstructing stones less likely. Ultrasound can be considered an initial screening test in patients with suspected nephrolithiasis to reduce the use of CT scans potentially. However, patients with moderate/severe hydronephrosis still require CT imaging due to poorer test sensitivity and moderate positive predictive value for larger stones requiring intervention.

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  • Isuru Hasantha

    I'm a graduate of B.Sc (Hons) in Nursing at the University of Peradeniya Sri Lanka. My research interests are Food Science, critical care Nursing, Microbiology and Community medicine.

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