title: Computerized tomography attenuation value of renal calculus: can it predict successful fragmentation of the calculus by extracorporeal shock wave lithotripsy? A preliminary study.
abstract: OBJECTIVE
  We evaluated the attenuation value of renal calculi on unenhanced axial computerized tomography (CT) images as a predictor of calculous fragmentation by extracorporeal shockwave lithotripsy (ESWL) (Dornier Medical Systems, Inc., Marietta, Georgia).
  
  
  METHODS
  We included 30 patients with renal calculi up to 20 mm. in this prospective study. Calculous attenuation value was measured in Hounsfield units on unenhanced CT sections through the calculi. Patients were subsequently treated with ESWL.
  
  
  RESULTS
  Patients were grouped according to calculous attenuation value as groups 1-less than 500, 2-500 to 1,000 and 3-greater than 1,000 Hounsfield units. Of the 30 patients 24 (80%) underwent successful treatment. The rate of stone clearance was 100% (12 of 12 cases) in group 1, 85.7% (6 of 7) in group 2 and 54.5% (6 of 11) in group 3. The success rate for stones with an attenuation value of greater than 1,000 Hounsfield units was significantly lower than that for stones with a value of less than 1,000 Hounsfield units (6 of 11 versus 18 of 19 cases, chi-square 7.07, p <0.01). Patients in group 3 required a greater median number of shock waves for stone fragmentation than those in groups 1 and 2 (7,300, 2,500, and 3,390, respectively). The mean attenuation value and number of shock waves required for calculous fragmentation correlated significantly (r = 0.779, p <0.001).
  
  
  CONCLUSIONS
  The CT attenuation value of renal calculi can help to differentiate stones that are likely to fragment easily on ESWL from those that would require a greater number of shock waves for fragmentation or may fail to fragment on ESWL.
authors.affiliation: Department of Urology, Postgraduate Institute of Medical Education and Research, and MRI and CT Scan Centre, Chandigarh, India.
authors.forename: Peter
authors.initials: P
authors.lastname: Joseph
authors.forename: A K
authors.initials: AK
authors.lastname: Mandal
authors.forename: S K
authors.initials: SK
authors.lastname: Singh
authors.forename: Purabi
authors.initials: P
authors.lastname: Mandal
authors.forename: S N
authors.initials: SN
authors.lastname: Sankhwar
authors.forename: S K
authors.initials: SK
authors.lastname: Sharma
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000000981:diagnostic imaging* / Q000628:therapy; D008096:Lithotripsy; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D019233:Retreatment; D014057:Tomography, X-Ray Computed