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Ultrasound is the standard investigation done in the diagnosis and follow-up of urinary calculi. But researchers at the department of urology, St. Michael’s Hospital, University of Toronto suggest that ultrasound may not be the most reliable investigation in the management of renal stones.

According to them, the two promimant disadvantages of ultrasound when compared to computed tomography in renal stones management are:

1. Overestimation of stone size: When compared with axial unenhanced CT, ultrasound shows the size to be bigger than the actual size which can lead to unnecessary surgical interventions in cases where only conservative management is warranted. Thus the authors advise against for planning treatment based solely on ultrasonography (US) findings. The study also found that the skin-stone distance, ie the distance between the ultrasound probe over the skin and the position of the calculi, is a significant factor determining the magnitute of the error. The error was not dependent on the body mass index and location of the calculi in the urinary tract.

2. Poor sensitivity and specificity for kidney and ureter stones: The team found that the sensitivity and specificity of US for the detection of ureteric calculi was 45% and 94%, respectively, and for the detection of renal calculi was 45% and 88%, respectively. Thus they consider US as not that worthy during an initial workup in the diagnosis of renal stones.

The authors found that CT is superior to ultrasound and US may be limited to:

• pregnant and pediatric patients where exposure to radiation is harmful.
• follow-up of translucent urinary calculi.
• in cases of hydronephrosis
• when there is need for repeated CT