title: Stone attenuation value and cross-sectional area on computed tomography predict the success of shock wave lithotripsy.
abstract: OBJECTIVE
  To identify the parameters on noncontrast computed tomography (NCCT) that best predict the success of shock wave lithotripsy (SWL).
  
  
  METHODS
  We reviewed the records of 75 patients who underwent SWL for urinary calculi measuring 5 to 20 mm. Using NCCT images, we estimated the largest stone cross-sectional area and contoured the inner edge of the stone. Clinical outcome was classified as successful (stone-free or <4 mm in diameter) or failed (stone fragments, ≥4 mm). The impact of preoperative parameters was evaluated by univariate and multivariate analysis.
  
  
  RESULTS
  The overall success rate was 73.3%. Average stone attenuation value, stone length, and stone cross-sectional area in the success and failure groups were 627.4±166.5 HU (Hounsfield unit) vs. 788.1±233.9 HU (p=0.002), 11.7±3.8 mm vs. 14.2±3.6 mm (p=0.015), and 0.31±0.17 cm(2) vs. 0.57±0.41 cm(2) (p<0.001), respectively. In the multivariate analysis, stone attenuation value was the only independent predictor of SWL success (p=0.023), although stone cross-sectional area had a tendency to be associated with SWL success (p=0.053). Patients were then classified into four groups by using cutoff values of 780 HU for stone attenuation value and 0.4 cm(2) for cross-sectional area. By use of these cutoff values, the group with a low stone attenuation value and a low cross-sectional area was more than 11.6 times as likely to have a successful result on SWL as were all other groups (odds ratio, 11.6; 95% confidence interval, 3.9 to 54.7; p<0.001).
  
  
  CONCLUSIONS
  Stone attenuation value and stone cross-sectional area are good predictors of extracorporeal SWL outcome.
authors.affiliation: Department of Urology, Juntendo University, Tokyo, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Tanaka
authors.forename: Eisuke
authors.initials: E
authors.lastname: Yokota
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Toyonaga
authors.forename: Fumitaka
authors.initials: F
authors.lastname: Shimizu
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Ishii
authors.forename: Makoto
authors.initials: M
authors.lastname: Fujime
authors.forename: Shigeo
authors.initials: S
authors.lastname: Horie
keywords: Noncontrast computed tomography; Treatment outcome