title: Lower pole ratio: a new and accurate predictor of lower pole stone clearance after shockwave lithotripsy?
abstract: BACKGROUND
  Lower pole spatial anatomy is an important determinant of success after extracorporeal shockwave lithotripsy. In the present study, we determine whether there is a significant relationship between lower pole ratio (infundibular length : infundibular width) on preoperative intravenous urograms and stone fragment clearances after shockwave lithotripsy.
  
  
  METHODS
  A total of 42 patients with isolated lower pole stones were retrospectively reviewed. Anatomical factors, such as infundibular length, width and infundibulopelvic angle were measured and the lower pole ratio was calculated on pretreatment intravenous urogram. Stone fragment clearance was assessed at three months with a plain abdominal X-ray.
  
  
  RESULTS
  The overall three-month stone-free rate was 62%. Mean stone size +/- SD was 10 +/- 4.8 mm, mean infundibular length was 21.7 +/- 6.9 mm, mean infundibular width was 6.1 +/- 2.3 mm, mean infundibulopelvic angle was 62.1 +/- 30.1 degrees and mean lower pole ratio was 4.3 +/- 2.8. Stone-free status after shockwave lithotripsy was significantly related to infundibular length and width as well as to lower pole ratio, but not to infundibulo-pelvic angle. Infundibular length less than 30 mm, width greater than 5 mm and lower pole ratio less than 3.5 were noted to have an improved three-month stone-free rate (P = 0.049, 0.01 and <0.01, respectively).
  
  
  CONCLUSIONS
  Caliceal anatomy is an important consideration for lower pole stone clearance after shockwave lithotripsy. The present study suggests that a lower pole ratio of less than 3.5, which considers both infundibular length and width, is a promising predictor for stone-free status.
authors.affiliation: Department of Urology, Changi General Hospital, 2 Simei Street 3, Singapore 529889. excelsurg@hotmail.com
authors.forename: Yan Kit
authors.initials: YK
authors.lastname: Fong
authors.forename: Sam Oon Hui
authors.initials: SO
authors.lastname: Peh
authors.forename: Siew Hong
authors.initials: SH
authors.lastname: Ho
authors.forename: Foo Cheong
authors.initials: FC
authors.lastname: Ng
authors.forename: Pearllyn Leng Choo
authors.initials: PL
authors.lastname: Quek
authors.forename: Kok Kit
authors.initials: KK
authors.lastname: Ng
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging*; D007669:Kidney Calculi / Q000000981:diagnostic imaging* / Q000628:therapy*; D008096:Lithotripsy; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D016896:Treatment Outcome; D014567:Urography