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Role of computed tomography with no contrast medium enhancement in predicting the outcome of extracorporeal shock wave lithotripsy for urinary calculi

Created: 24/11/2006


Role of computed tomography with no contrast medium enhancement in predicting the outcome of extracorporeal shock wave lithotripsy for urinary calculi
Narmada P. Gupta, Mohd S. Ansari, Pawan Kesarvani, Annu Kapoor and Seema Mukhopadhyay
BJU International Volume 95 Page 1285 - June 2005


  • The outcome of ESWL depends on many factors, including stone size, location, composition, fragility, the shock wave generator and the presence of obstruction or infection
  • Stone composition has emerged as the main factor influencing the efficacy of ESWL
  • CT with no enhancement by contrast medium (NCCT) is now the preferred method to evaluate patients with renal colic
  • The ability of NCCT to detect density differences as low as 0.5% has been exploited to determine the composition and fragility of urinary stones
  • The density of the stone varies with composition, and affects the fragility of a calculus, which ultimately governs the clinical outcome in ESWL
  • This paper evaluates the role of NCCT, using the attenuation value, in determining the fragility and clearance of calculi in patients treated with ESWL

Patients and Methods

  • 112 patients with solitary renal and upper ureteric calculi of 0.5–2 cm undergoing ESWL were evaluated
  • All patients had NCCT at 120 kV and 240 mA on a spiral CT scanner
  • During each ESWL session 3000 shock waves were given to a maximum of 3.0 kV
  • X-ray of the kidney, ureters and bladder was taken 12 weeks after the last ESWL session
  • Fragments of = 5 mm were regarded as clinically insignificant residual fragments (CIRF)
  • The calculi retrieved were analysed by X-ray diffraction and the results assessed by comparing the mean density (as measured in Hounsfield units, HU) with the number of ESWL sessions and clearance


  • 82 (76%) patients had complete clearance of stones
  • 26 (24%) had CIRF
  • There was a linear relationship between the calculus density and number of ESWL sessions required
  • Patients with calculi of = 750 HU, 41 (80%) needed three or fewer ESWL sessions and 45 (88%) had complete clearance
  • Patients with calculi of > 750 HU, 41 (72%) required three or more ESWL sessions, and 37 (65%) had complete clearance
  • Best outcomes were in patients with calculus diameters of < 1.1 cm and mean densities of = 750 HU
    • 34 (83%) needed three or fewer ESWL sessions, and the clearance rate was 90%
  • Worst outcomes were in patients with calculus densities of > 750 HU and diameters of > 1.1 cm
    • 23 (77%) needed three or more ESWL sessions and the clearance rate was only 60%
  • The calculus density was a stronger predictor of outcome than size alone


  • Outcome of ESWL is measured in terms of fragmentation and clearance fragments
  • Fragmentation depends on stone size and composition and the ability to predict stone composition would help to increase the efficiency of ESWL
  • Previous studies using plain xrays have shown the stone-free rates for smooth, radiologically dense calculi and calculi with irregular outlines are 34% and 79%, respectively
  • However, the overall accuracy of predicting calculus composition from plain radiographs has been reported to be only 39%, which is at present insufficient for clinical use
  • NCCT can detect density differences of 0.5%, whereas plain radiography requires a density difference of ˜ 5%
  • Identifying uric acid calculi is feasible by NCCT, but overlapping CT attenuation values for different calcium calculi make their identification difficult
  • Few clinical studies have compared the density of calculi with the outcome of ESWL in vivo
  • In the present study, when patients were categorised by calculus density, 80% with calculi of = 750 HU needed three or fewer ESWL sessions and 88% had complete clearance. Conversely, of patients with calculi of > 750 HU, 72% required three or more sessions for complete clearance
  • Patients with a mean stone density of > 750 HU had 10.5 times more chance of requiring three or more sessions than patients with mean stone densities of = 750 HU
  • Therefore, for calculi of = 750 HU, irrespective of size (<2 cm), ESWL should be the preferred treatment
  • Calculi of > 750 HU are associated with a poor outcome when treated with ESWL and an alternative treatment like percutaneous nephrolithotomy and/or ureteroscopy

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