title: Diagnostic value of attenuation measurements of the kidney on unenhanced helical CT of obstructive ureterolithiasis.
abstract: OBJECTIVE
  The objective of this study was to assess the diagnostic value of attenuation measurements of the kidney on unenhanced helical CT in patients with obstructive ureterolithiasis.
  
  
  METHODS
  Consecutive unenhanced helical CT scans of patients referred for acute unilateral renal colic were retrospectively reviewed. Patients with CT evidence of other urinary system diseases were excluded. Included scans (n = 145) were assessed for ureteral stone and secondary signs of obstruction such as unilateral collecting system or ureteral dilatation, perinephric stranding, and periureteral edema. Renal attenuation in Hounsfield units was measured in the upper, middle, and lower portions of the parenchyma, and a mean value was determined for each kidney.
  
  
  RESULTS
  Ureteral stones were present in 76 patients. Renal attenuation on the side with lithiasis was lower than on the opposite kidney: 27.2 +/- 3.9 H vs 32.6 +/- 3.4 H (p < 0.001). Attenuation differences between kidneys were higher for patients with ureterolithiasis: 5.4 +/- 3.2 H (range, -3.3 to 13.0 H) versus 1.2 +/- 1.0 H (range, 0-4.7 H) (p < 0.001). An attenuation difference between kidneys greater than or equal to 5.0 H had 61% sensitivity, 100% specificity, 100% positive predictive value, 69% negative predictive value, and 79% accuracy for diagnosis of ureteral lithiasis.
  
  
  CONCLUSIONS
  Attenuation difference between kidneys greater than or equal to 5.0 H was a valuable sign and had diagnostic performance similar to other secondary signs of obstructive ureterolithiasis. Furthermore, attenuation difference had the advantage of being an objective, measurement-based indicator.
authors.affiliation: Department of Radiology, Federal University of São Paulo School of Medicine, Rua Napoleão de Barros 800, São Paulo CEP 04024-002, Brazil.
authors.forename: Suzan M
authors.initials: SM
authors.lastname: Goldman
authors.forename: Salomão
authors.initials: S
authors.lastname: Faintuch
authors.forename: Sergio A
authors.initials: SA
authors.lastname: Ajzen
authors.forename: Dejaldo M J
authors.initials: DM
authors.lastname: Christofalo
authors.forename: Marcelo P
authors.initials: MP
authors.lastname: Araújo
authors.forename: Valdemar
authors.initials: V
authors.lastname: Ortiz
authors.forename: Miguel
authors.initials: M
authors.lastname: Srougi
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Kenney
authors.forename: Jacob
authors.initials: J
authors.lastname: Szejnfeld
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D014514:Ureteral Calculi / Q000150:complications / Q000000981:diagnostic imaging*; D014517:Ureteral Obstruction / Q000000981:diagnostic imaging* / Q000209:etiology