title: The Cumulated Stone Diameter: A Limited Tool for Stone Burden Estimation.
abstract: OBJECTIVE
  To compare the performance of the main methods used to estimate stone burden in order to improve and standardize preoperative evaluation of stone disease.
  
  
  METHODS
  From January 2012 to June 2013, a series of consecutive retrograde intrarenal stone surgery was prospectively evaluated at a single institute. All patients had a pre- and postoperative CT scan. The stone burden was estimated using 3 methods: the cumulative stone diameter (M1), Ackermann's formula (M2), and the sphere formula (M3). The predictive value of the postoperative stone-free status of these methods was then compared.
  
  
  RESULTS
  Overall (n = 142), the stone-free rate was 64%. The three methods (M1, M2, and M3) were all predictive of stone-free status for stones <20 mm (P = .0076, .018, and .016, respectively). However, only M2 and M3 were significant for stones >20 mm (P = .0024 and .023). Using receiver operating characteristic curves, we found that areas under the curve were 0.73, 0.70, and 0.71 for stones below 20 mm and 0.53, 0.74, and 0.74 for stones above 20 mm for M1, M2, and M3, respectively. In multivariate analysis, M1 and M3 were both found to be independently associated with the stone-free status in the whole series (P <.001 and .011, respectively). However, for stones above 20 mm, only M3 was significant (P = .020).
  
  
  CONCLUSIONS
  Evaluation of the stone burden is an important predictor of the outcome of retrograde intrarenal stone surgery. For stones below 20 mm, all the three methods approximate stone burden correctly; however, for the stones above 20 mm, calculation of volume is recommended.
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Merigot de Treigny
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France.
authors.forename: Elie
authors.initials: E
authors.lastname: Bou Nasr
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Almont
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Tack
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Rischmann
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Soulié
authors.affiliation: Hôpital Rangueil University Medical Center, Toulouse, France. Electronic address: eric.huyghe@yahoo.fr.
authors.forename: Eric
authors.initials: E
authors.lastname: Huyghe
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000473:pathology* / Q000601:surgery; D008297:Male; D008432:Mathematical Computing; D008875:Middle Aged; D018579:Patient Selection; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012372:ROC Curve; D012720:Severity of Illness Index; D014057:Tomography, X-Ray Computed