title: Normal ureter size on unenhanced helical CT.
abstract: OBJECTIVE
  Unenhanced helical CT is the imaging method of choice when evaluating patients with acute flank pain and suspected ureterolithiasis. In addition to directly identifying stones in the lumen of the ureter, CT secondary signs of obstruction such as ureteral dilatation are frequently present and can be helpful in establishing a diagnosis. The purposes of this study were to define ureteral dilatation on unenhanced helical CT and determine the range of normal ureter size.
  
  
  METHODS
  We retrospectively reviewed the unenhanced helical CT studies of 212 consecutive patients with acute flank pain whose CT scans showed acute ureterolithiasis. The size of the ureter was determined on the asymptomatic side as well as on the obstructed side. Mean ureteral diameter was determined as the largest transverse dimension along the course of the ureter beginning 1-2 cm below the ureteropelvic junction.
  
  
  RESULTS
  The mean size of ureters on the asymptomatic side was 1.8 mm with a standard deviation (SD) of 0.9 mm. The mean size of ureters on the obstructed side was 7 mm with an SD of 3.2 mm. In 96% of patients, the ureter diameter on the asymptomatic side was 3 mm or smaller.
  
  
  CONCLUSIONS
  Three millimeters should be considered the upper limit of normal size for nonobstructed ureters on unenhanced helical CT.
authors.affiliation: Weill Medical College of Cornell University, 420 E 70th St., New York, NY 10021, USA. nam2001@med.cornel.edu
authors.forename: Natalie
authors.initials: N
authors.lastname: Zelenko
authors.forename: Deidre
authors.initials: D
authors.lastname: Coll
authors.forename: Arthur T
authors.initials: AT
authors.lastname: Rosenfeld
authors.forename: Robert C
authors.initials: RC
authors.lastname: Smith
mesh_terms: D004108:Dilatation, Pathologic / Q000000981:diagnostic imaging; D021501:Flank Pain / Q000000981:diagnostic imaging / Q000209:etiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012189:Retrospective Studies; D036542:Tomography, Spiral Computed; D014513:Ureter / Q000000981:diagnostic imaging* / Q000473:pathology*; D014514:Ureteral Calculi / Q000150:complications / Q000000981:diagnostic imaging*; D014517:Ureteral Obstruction / Q000000981:diagnostic imaging* / Q000209:etiology