title: MR imaging in the characterization of small renal masses.
abstract: OBJECTIVE
  The aim of our study was to evaluate the effectiveness of MR imaging for the characterization of small (<2 cm) renal lesions described as indeterminate on prior US or CT.
  
  
  METHODS
  Sixty-three small renal masses in 51 patients considered indeterminate on prior ultrasound or CT scans were included in the study. A retrospective evaluation of the examinations was performed independently by two body magnetic resonance imaging (MRI) radiologists who were unaware of the final diagnosis. A 3-point confidence scale (1: benign, 2: indeterminate, and 3: malignant) was established to determine the level of suspicion for malignancy. Interobserver agreement was determined with a weighted kappa statistic. The diagnosis was verified by imaging follow-up of at least 24 months (mean 60 months) in 53 lesions and by pathology in 10 lesions.
  
  
  RESULTS
  MRI detected all eight malignancies in the series. There were eight malignant lesions and two benign lesions among those with pathologic follow-up. No interval growth or evidence of malignancy in the remaining 53 lesions was found for a minimum of 24 months by repeat imaging. The sensitivity, specificity, positive predictive value, and negative predictive value of MRI for differentiating benign from malignant small renal lesions were 100% (62.9-100%, 95% CI), 94.5% (84.9-98.8%, 95% CI), 72.7% (39.1-93.6%, 95% CI), and 100% (93.1-100%, 95% CI), respectively. The kappa value for interobserver agreement was 0.77 (95% CI 0.59-0.96, p-value <0.001).
  
  
  CONCLUSIONS
  MR imaging is an effective method for characterizing small (<2 cm) renal masses found to be indeterminate by US or CT.
authors.affiliation: Department of Radiology, University of Michigan, Ann Arbor, MI, USA, jwillatt@med.umich.edu.
authors.forename: Jonathon M
authors.initials: JM
authors.lastname: Willatt
authors.forename: Hero K
authors.initials: HK
authors.lastname: Hussain
authors.forename: Suzanne
authors.initials: S
authors.lastname: Chong
authors.forename: Mariam
authors.initials: M
authors.lastname: Kappil
authors.forename: Shadi F
authors.initials: SF
authors.lastname: Azar
authors.forename: Peter S
authors.initials: PS
authors.lastname: Liu
authors.forename: Julie A
authors.initials: JA
authors.lastname: Ruma
authors.forename: Khaled M
authors.initials: KM
authors.lastname: Elsayes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media; D003937:Diagnosis, Differential; D005260:Female; D005682:Gadolinium; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D007668:Kidney / Q000473:pathology*; D007674:Kidney Diseases / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult
chemical_list: D003287:Contrast Media; D005682:Gadolinium